75 min read

A Comprehensive Introduction to Command Line for R Users

2019/10/26

In this tutorial, you will be introduced to the command line. We have selected a set of commands we think will be useful in general to a wide range of audience. We have created a RStudio Cloud Project to ensure that all readers are using the same environment while going through the tutorial. Our goal was to ensure that after completing this tutorial, readers should be able to use the shell for version control, managing cloud services (like deploying your own shiny server etc.), execute commands in R & RMarkdown and execute R scripts in the shell. Apart from learning shell commands, the tutorial will also focus on

  • exploring R release names
  • mapping shell commands to R functions
  • RStudio Terminal
  • executing shell commands from R using system2() or processx::run()
  • execute shell commands in RMarkdown
  • execute R scripts in the shell

If you want a deeper understanding of using command line for data science, we suggest you read Data Science at the Command Line. Software Carpentry too has a lesson on shell. We have listed more references at the end of the tutorial for the benefit of the readers.

Resources

Below are the links to all the resources related to this post:

You can try our free online course Command Line Basics for R Users if you prefer to learn through self paced online courses or our ebook if you like to read the tutorial in a book format.

Introduction

What is Shell/Terminal?

Shell is a text based application for viewing, handling & manipulating files. It takes in commands and passes them on to the operating system. It is also known as

  • CLI (Command Line Interface)
  • Bash (Bourne Again Shell)
  • Terminal

It is sufficient to know a handful of commands to get started with the shell.

Launch Terminal

Although we will use the terminal in RStudio on RStudio Cloud, we should still know how to launch the terminal in different operating systems.

mac

Applications -> Utility -> Terminal

Windows

Option 1

Go to the Start Menu or screen and enter Command Prompt in the search field.

Option 2

Start Menu -> Windows System -> Command Prompt

Option 3

Hold the Windows key and press the R key to get a Run window. Type cmd in the box and click on the OK button.

Linux

  • Applications -> Accessories -> Terminal
  • Applications -> System -> Terminal

Windows Subsystem for Linux

If you want to use bash on Windows, try the Windows subsystem for Linux. It only works on 64 bit Windows 10. Below are the steps to enable Windows subsystem fro Linux:

Step 1 - Enable Developer Mode

To enable Developer Mode open the Settings app and head to Update & Security > For Developers. Press the Developer Mode switch.

Step 2 - Enable Windows Subsystem for Linux

To enable the Windows Subsystem for Linux (Beta), open the Control Panel, click Programs and Features, and click Turn Windows Features On or Off in left side bar under Programs and Features. Enable the Windows Subsystem for Linux (Beta) option in the list here and click OK. After you do, you’ll be prompted to reboot your computer. Click Restart Now to reboot your computer and Windows 10 will install the new feature.

Step 3 - Install your Linux Distribution of Choice

Open the Microsoft store and choose your favorite Linux distribution.

In the distro’s page, click on “Get”.

Launch the distro from the Start Menu.

You can learn more about the Windows Subsystem for Linux here.

RStudio Terminal

RStudio introduced the terminal with version 1.1.383. The terminal tab is next to the console tab. If it is not visible, use any of the below methods to launch it

  • Shift + Alt + T
  • Tools -> Terminal -> New Terminal

Note, the terminal depends on the underlying operating system. To learn more about the RStudio terminal, read this article or watch this webinar. In this book, we will use the RStudio terminal on RStudio Cloud to ensure that all users have access to Linux bash. You can try all the commands used in this book on your local system as well except in case of Windows users.

Prompt

As soon as you launch the terminal, you will see the hostname, machine name and the prompt. In case of mac & Linux users, the prompt is $. For Windows users, it is >.

OS Prompt
macOS $
Linux $
Windows >

Get Started

To begin with, let us learn to display

  • basic information about the user
  • the current date & time
  • the calendar
  • and clear the screen.
Command Description
whoami Who is the user?
date Get date, time and timezone
cal Display calendar
clear Clear the screen

whoami prints the effective user id i.e. the name of the user who runs the command. Use it to verify the user as which you are logged into the system.

whoami
## aravind

date will display or change the value of the system’s time and date information.

date
## Wed Jun 10 22:45:47 IST 2020

cal will display a formatted calendar and clear will clear all text on the screen and display a new prompt. You can clear the screen by pressing Ctrl + L as well.

cal

In R, we can get the user information from Sys.info() or whoami() from the whoami package. The current date & time are returned by Sys.date() & Sys.time(). To clear the R console, we use Ctrl + L.

Command R
whoami Sys.info() / whoami::whoami()
date Sys.date() / Sys.time()
cal
clear Ctrl + L

Help/Documentation

Before we proceed further, let us learn to view the documentation/manual pages of the commands.

Command Description
man Display manual pages for a command
whatis Single line description of a command

man is used to view the system’s reference manual. Let us use it to view the documentation of the whatis command which we will use next.

man whatis
## WHATIS(1)                     Manual pager utils                     WHATIS(1)
## 
## NAME
##        whatis - display one-line manual page descriptions
## 
## SYNOPSIS
##        whatis  [-dlv?V]  [-r|-w]  [-s  list]  [-m  system[,...]] [-M path] [-L
##        locale] [-C file] name ...
## 
## DESCRIPTION
##        Each manual page has a short description available within  it.   whatis
##        searches  the  manual  page names and displays the manual page descrip‐
##        tions of any name matched.
## 
##        name may contain wildcards (-w) or be a regular expression (-r).  Using
##        these  options, it may be necessary to quote the name or escape (\) the
##        special characters to stop the shell from interpreting them.
## 
##        index databases are used during the search,  and  are  updated  by  the
##        mandb  program.   Depending  on your installation, this may be run by a
##        periodic cron job, or may need to be  run  manually  after  new  manual
##        pages  have  been installed.  To produce an old style text whatis data‐
##        base from the relative index database, issue the command:
## 
##        whatis -M manpath -w '*' | sort > manpath/whatis
## 
##        where manpath is a manual page hierarchy such as /usr/man.
## 
## OPTIONS
##        -d, --debug
##               Print debugging information.
## 
##        -v, --verbose
##               Print verbose warning messages.
## 
##        -r, --regex
##               Interpret each name as a regular expression.  If a name  matches
##               any  part  of  a  page  name, a match will be made.  This option
##               causes whatis to be somewhat slower due to the nature  of  data‐
##               base searches.
## 
##        -w, --wildcard
##               Interpret  each  name  as a pattern containing shell style wild‐
##               cards.  For a match to be made, an expanded name must match  the
##               entire  page  name.   This  option  causes whatis to be somewhat
##               slower due to the nature of database searches.
## 
##        -l, --long
##               Do not trim output to the terminal width.  Normally, output will
##               be  truncated  to  the terminal width to avoid ugly results from
##               poorly-written NAME sections.
## 
##        -s list, --sections list, --section list
##               Search only the given manual sections.   list  is  a  colon-  or
##               comma-separated list of sections.  If an entry in list is a sim‐
##               ple section,  for  example  "3",  then  the  displayed  list  of
##               descriptions  will include pages in sections "3", "3perl", "3x",
##               and so on; while if an entry in list has an extension, for exam‐
##               ple "3perl", then the list will only include pages in that exact
##               part of the manual section.
## 
##        -m system[,...], --systems=system[,...]
##               If this system has access to  other  operating  system's  manual
##               page  names,  they can be accessed using this option.  To search
##               NewOS's manual page names, use the option -m NewOS.
## 
##               The system specified can be a  combination  of  comma  delimited
##               operating system names.  To include a search of the native oper‐
##               ating system's manual page names, include the system name man in
##               the  argument  string.   This  option  will override the $SYSTEM
##               environment variable.
## 
##        -M path, --manpath=path
##               Specify an alternate set of colon-delimited manual page  hierar‐
##               chies  to search.  By default, whatis uses the $MANPATH environ‐
##               ment variable, unless it is empty or unset,  in  which  case  it
##               will  determine an appropriate manpath based on your $PATH envi‐
##               ronment variable.  This option overrides the contents  of  $MAN‐
##               PATH.
## 
##        -L locale, --locale=locale
##               whatis  will normally determine your current locale by a call to
##               the C function setlocale(3) which interrogates various  environ‐
##               ment  variables,  possibly including $LC_MESSAGES and $LA

whatis displays short manual page descriptions (each manual page has a short description available within it).

whatis ls
## ls (1)               - list directory contents

You will find tldr.sh very useful while exploring new commands and there is a related R package, tldrrr as well.

# devtools::install_github("kirillseva/tldrrr")
tldrrr::tldr("pwd")
## pwd 
##  
## Print name of current/working directory. 
##  
## • Print the current directory: 
##  
##   pwd 
##  
## • Print the current directory, and resolve all symlinks (i.e. show the "physical" path): 
##  
##   pwd -P

new courses ad

File Management

In this section, we will explore commands for file management including:

  • create new file/change timestamps
  • copying files
  • renaming/moving files
  • deleting files
  • comparing files
Command Description
touch Create empty file(s)/change timestamp
cp Copy files & folders
mv Rename/move file
rm Remove/delete file
diff Compare files

Create new file

touch modifies file timestamps which is information associated with file modification. It can be any of the following:

  • access time (the last time the file was read)
  • modification time (the last time the contents of the file was changed)
  • change time (the last time the file’s metadata was changed)

If the file does not exist, it will create an empty file of the same name. Let us use touch to create a new file myanalysis.R.

touch myanalysis.R
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myanalysis.R
## myfiles
## mypackage
## myproject
## myproject1
## myproject2
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Copy Files/Folders

cp makes copies of files and directories. The general form of the command is cp source destination. By default, it will overwrite files without prompting for confirmation so be cautious while copying files or folders.

Copy files in same folder

Let us create a copy of release_names.txt file and name it as release_names_2.txt.

cp release_names.txt release_names_2.txt
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myanalysis.R
## myfiles
## mypackage
## myproject
## myproject1
## myproject2
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## release_names_2.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Copy files into different folder

To copy a file into a different directory/folder, we need to specify the name of the destination folder. If the copied file should have a different name, then we need to specify the new name of the file as well. Let us copy the release_names.txt file into the r_releases folder (we will retain the same name for the file as we are copying it into a different folder).

cp release_names.txt r_releases/release_names.txt

Let us check if the file has been copied by listing the files in the r_releases folder using ls.

ls r_releases
## release_names.txt

Copy folders

How about making copies of folders? Use the -r option to copy entire folders. Let us create a copy of the r folder and name it as r2. The -r option stands for --recursive i.e. copy directories recursively.

cp -r r r2
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myanalysis.R
## myfiles
## mypackage
## myproject
## myproject1
## myproject2
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## release_names_2.txt
## release_names_3.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Move/Rename Files

mv moves and renames files and directories. Using different options, we can ensure

  • files are not overwritten
  • user is prompted for confirmation before overwriting files
  • details of files being moved is displayed
Command Description
mv Move or rename files/directories
mv -f Do not prompt for confirmation before overwriting files
mv -i Prompt for confirmation before overwriting files
mv -n Do not overwrite existing files
mv -v Move files in verbose mode

Let us move the release_names_2.txt file to the r_releases folder.

mv release_names_2.txt r_releases

Use ls to verfiy if the file has been moved. As you can see, release_names_2.txt is not present in the current working directory.

ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myanalysis.R
## myfiles
## mypackage
## myproject
## myproject1
## myproject2
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## release_names_3.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Let us check if release_names_2.txt is present in the r_releases folder. Great! We have successfully moved the file into a different folder.

ls r_releases
## release_names.txt
## release_names_2.txt

Move files in verbose mode

To view the details of the files being moved/renamed, use the -v option. In the below example, we move the release_names_3.txt file into the r_releases folder using mv.

mv -v release_names_3.txt r_releases
## renamed 'release_names_3.txt' -> 'r_releases/release_names_3.txt'

Do not overwrite existing files

How do we ensure that files are not overwritten without prompting the user first? In the below example, we will try to overwrite the release_names_2.txt in the r_releases folder using mv and see what happens. But first, let us look at the contents of the release_names_2.txt file using the cat command.

We will look into the cat command in more detail in the next chapter but for the time being it is sufficient to know that it prints contents of a file. The file contains release names of different R versions.

cat r_releases/release_names_2.txt
## Unsuffered Consequences
## Great Pumpkin
## December Snowflakes
## Gift-Getting Season
## Easter Beagle
## Roasted Marshmallows
## Trick or Treat
## Security Blanket
## Masked Marvel
## Good Sport
## Frisbee Sailing
## Warm Puppy
## Spring Dance
## Sock it to Me
## Pumpkin Helmet
## Smooth Sidewalk
## Full of Ingredients
## World-Famous Astronaut
## Fire Safety
## Wooden Christmas Tree
## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

In our current working directory, we will create another file of the same name i.e. release_names_2.txt but its contents are different from the file in the r_releases folder. It contains the string release_names and nothing else. We will now move this file into the r_releases folder but use the option -n to ensure that the file in the r_releases folder is not overwritten. We can confirm this by printing the contents of the file in the r_releases folder.

The echo command is used to print text to the terminal or to write to a file. We will explore it in more detail in the next chapter.

echo "release_names" > release_names_2.txt 
mv -n release_names_2.txt r_releases
cat r_releases/release_names_2.txt
## Unsuffered Consequences
## Great Pumpkin
## December Snowflakes
## Gift-Getting Season
## Easter Beagle
## Roasted Marshmallows
## Trick or Treat
## Security Blanket
## Masked Marvel
## Good Sport
## Frisbee Sailing
## Warm Puppy
## Spring Dance
## Sock it to Me
## Pumpkin Helmet
## Smooth Sidewalk
## Full of Ingredients
## World-Famous Astronaut
## Fire Safety
## Wooden Christmas Tree
## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

As you can observe, the contents of the file in the r_releases folder has not changed. In the next section, we will learn to overwrite the contents using the -f option.

Do not prompt for confirmation before overwriting files

What if we actually intend to overwrite a file and do not want to be prompted for confirming the same. In this case, we can use the -f option which stands for --force i.e. do not prompt before overwriting. Let us first print the contents of the release_names_2.txt file in the r_releases folder.

cat r_releases/release_names_2.txt
## Unsuffered Consequences
## Great Pumpkin
## December Snowflakes
## Gift-Getting Season
## Easter Beagle
## Roasted Marshmallows
## Trick or Treat
## Security Blanket
## Masked Marvel
## Good Sport
## Frisbee Sailing
## Warm Puppy
## Spring Dance
## Sock it to Me
## Pumpkin Helmet
## Smooth Sidewalk
## Full of Ingredients
## World-Famous Astronaut
## Fire Safety
## Wooden Christmas Tree
## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

Now we will create another file of the same name in the current working directory but with different content and use the -f option to overwrite the file in the r_releases folder. You can see that the contents of the file in the r_releases folder has changed.

echo "release_names" > release_names_2.txt 
mv -f release_names_2.txt r_releases
cat r_releases/release_names_2.txt
## release_names

Remove/Delete Files

The rm command is used to delete/remove files & folders. Using additional options, we can

  • remove directories & sub-directories
  • forcibly remove directories
  • interactively remove multiple files
  • display information about files removed/deleted
Command Description
rm Remove files/directories
rm -r Recursively remove a directory & all its subdirectories
rm -rf Forcibly remove directory without prompting for confirmation or showing error messages
rm -i Interactively remove multiple files, with a prompt before every removal
rm -v Remove files in verbose mode, printing a message for each removed file

Remove files

Let us use rm to remove the file myanalysis.R (we created it earlier using the touch command).

rm myanalysis.R
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject1
## myproject2
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Recursive Deletion

How about folders or directories? We can remove a directory and all its contents including sub-directories using the option -r which stands for --recursive and removes directories and their contents recursively. Let us remove the myproject1 folder and all its contents.

rm -r myproject1
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject2
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Force Removal

Use the -f option which stands for --force to forciby remove directory and all its contents without prompting for confirmation or showing error messages. Let us remove the myproject2 folder and all its contents.

rm -rf myproject2
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Verbose Mode

Remove files in verbose mode, printing a message for each removed file. This is useful when you want to see the details of the files being removed. In the below example, we will remove all files with .txt extension from the myfiles folder. Instead of specifying the name of each text file, we use the wildcard * along with .txt i.e. any file with the extension .txt will be removed.

cd myfiles
rm -v *.txt
## removed 'release_names.txt'
## removed 'release_names_18.txt'
## removed 'release_names_19.txt'

Compare Files

diff stands for difference. It is used to compare files line by line and display differences. It also indicates which lines in one file must be changed to make the files identical. Using additional options, we can

  • ignore white spaces while comparing files
  • show differences sidy by side
  • show differences in unified format
  • compare directories recursively
  • display names of files that differ
Command Description
diff Compare files & directories
diff -w Compare files; ignoring white spaces
diff -y Compare files; showing differences side by side
diff -u Compare files; show differences in unified format
diff -r Compare directories recursively
diff -rq Compare directories; show the names of files that differ

Compare Files

Let us compare the contents of the following files

  • imports_olsrr.txt
  • imports_blorr.txt

The files contain the names of R packages imported by the olsrr and blorr packages respectively (Full disclosure: both the above R pakages are developed by Rsquared Academy.).

diff uses certain special symbols and gives instructions to make the files identical. The instructions are on how to change the first file to make it identical to the second file. We list the symbols below

  • a for add
  • c for change
  • d for delete

We will use the -w option to ignore white spaces while comparing the files.

diff -w imports_olsrr.txt imports_blorr.txt
## 1a2
## > caret
## 3d3
## < cli
## 4a5
## > cli

Let us interpret the results. 4a5 indicates after line 4 in file 1, add line 5 from file 2 to make both the files identical i.e. add caret which is line 5 in imports_blorr.txt after line 4 in imports_olsrr.txt which will make both the files identical.

Let us change the file order and see the instructions from diff.

diff -w imports_blorr.txt imports_olsrr.txt
## 2d1
## < caret
## 4d2
## < clisymbols
## 5a4
## > clisymbols

5d4 indicates delete line 5 from file 1 to match both the files at line4 i.e. delete caret which is line 5 in imports_blorr.txt to make both the files identical.

Side By Side

To view the differences between the files side by side, use the -y option.

diff -y imports_olsrr.txt imports_blorr.txt
## car 
                                  | car
## checkmate
                                  | caret
## cli
                                  | checkmate
## clisymbols
                                  | clisymbols
##                                > cli

Unified Format

To view the differences between the files in a unified format, use the -u option.

diff -u imports_olsrr.txt imports_blorr.txt
## --- imports_olsrr.txt    2019-09-20 13:36:03.000000000 +0530
## +++ imports_blorr.txt    2019-09-20 13:36:35.000000000 +0530
## @@ -1,4 +1,5 @@
## -car 
## -checkmate
## -cli
## -clisymbols
## +car
## +caret
## +checkmate
## +clisymbols
## +cli

Compare Recursively

To compare recursively, use the -r option. Let us compare the mypackage and myproject folders.

diff -r mypackage myproject
## Only in mypackage: .Rbuildignore
## Only in mypackage: DESCRIPTION
## Only in mypackage: LICENSE
## Only in mypackage: NAMESPACE
## Only in mypackage: NEWS.md
## Only in mypackage: R
## Only in myproject/data: processed
## Only in myproject/data: raw
## Only in mypackage: docs
## Only in mypackage: man
## Only in myproject: output
## Only in myproject: run_analysis.R
## Only in mypackage: tests
## Only in mypackage: vignettes

File Details

To compare directories and view the names of files that differ, use the -rq option. In the below example, we look at the names of files that differ in mypackage and myproject folders.

diff -rq mypackage myproject
## Only in mypackage: .Rbuildignore
## Only in mypackage: DESCRIPTION
## Only in mypackage: LICENSE
## Only in mypackage: NAMESPACE
## Only in mypackage: NEWS.md
## Only in mypackage: R
## Only in myproject/data: processed
## Only in myproject/data: raw
## Only in mypackage: docs
## Only in mypackage: man
## Only in myproject: output
## Only in myproject: run_analysis.R
## Only in mypackage: tests
## Only in mypackage: vignettes

R Functions

In R, file operations can be performed using functions from both base R and the fs package.

Command R
touch file.create() / fs::file_create() / fs::file_touch()
cp file.copy() / fs::file_copy() / fs::dir_copy()
mv file.rename() / fs::file_move()
rm file.remove() / fs::file_delete()
diff

Input/Output

In this section, we will explore commands that will

  • display messages
  • print file contents
  • sort file contents
Command Description
echo Display messages
cat Print contents of a file
head Prints first ten lines of a file by default
tail Prints last ten lines of a file by default
more Open a file for interactive reading, scrolling & searching
less Open a file for interactive reading, scrolling & searching
sort Sort a file in ascending order

Display Messages

The echo command prints text to the terminal. It can be used for writing or appending messages to a file as well.

Command Description
echo Display messages
echo -n Print message without trailing new line
echo &gt; file Write message to a file
echo &gt;&gt; file Append message to a file
echo -e Enable interpretation of special characters

Redirect Output

What if we want to redirect the output? Instead of printing the text to the terminal, we want to write it to a file. In such cases, use > along with the file name to redirect the output to the file. Keep in mind that > will overwrite files. If you want to append to files instead of overwriting, use >>.

echo Great Truth > release.txt

Tail

The tail command displays the last 10 lines of a file(s) by default. It can be used to display the last few lines or bytes of a file as well.

Command Description
tail Display the last part of a file
tail -n num Show the last num lines of a file
tail -n +num Show all contents of the file starting from num line
tail -c num Show last num bytes of a file
tail -f Keep reading file until Ctrl + C
tail -F Keep reading file until Ctrl + C; even if the file is rotated

Display the last parts of a file

Let us use tail to display the last 10 lines of the file.

tail release_names.txt
## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

Display the last 5 lines of a file

As we did in the previous section, use n to specify the number of lines to be displayed.

tail -n 5 release_names.txt
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

Display all contents from line 10

We can use tail to display all contents of a file starting from a specific line. In the below example, we display all contents of the file starting from the 10th line using the n option and + prefix while specifying the number of lines.

tail -n +10 release_names.txt
## Good Sport
## Frisbee Sailing
## Warm Puppy
## Spring Dance
## Sock it to Me
## Pumpkin Helmet
## Smooth Sidewalk
## Full of Ingredients
## World-Famous Astronaut
## Fire Safety
## Wooden Christmas Tree
## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

Display the last 10 bytes of a file

Use the c option to display the last 7 bytes of a file.

tail -c 7 release_names.txt
##  Tree

More

The more command displays text, one screen at a time. It opens a file for

  • interactive reading
  • scrolling
  • and searching

Press space to scroll down the page, the forward slash (/) for searching strings, n to go to the next match and q to quit.

Command Description
more Open a file for interactive reading, scrolling & searching
space Page down
/ Search for a string; press n to go the next match
q Quit

Less

The less command is similar to more but offers more features. It allows the user to scroll up and down, go to the beggining and end of the file, forward and backward search and the ability to go the next and previous match while searching the file.

Command Description
less Open a file for interactive reading, scrolling & searching
space Page down
b Page up
G Go to the end of file
g Go to the start of file
/ Forward search
? Backward search
n Go to next match
N Go to previous match
q Quit

Sort

The sort command will sort the contents of text file, line by line. Using additional options, we can

  • sort a file in ascending/descending order
  • ignore case while sorting
  • use numeric order for sorting
  • preserve only unique lines while sorting

Using the sort command, the contents can be sorted numerically and alphabetically. By default, the rules for sorting are:

  • lines starting with a number will appear before lines starting with a letter.
  • lines starting with a letter that appears earlier in the alphabet will appear before lines starting with a letter that appears later in the alphabet.
  • lines starting with a lowercase letter will appear before lines starting with the same letter in uppercase.

Using additional options, the rules for sorting can be changed. We list the options in the below table.

Command Description
sort Sort lines of text files
sort -r Sort a file in descending order
sort --ignore-case Ignore case while sorting
sort -n Use numeric order for sorting
sort -u Preserve only unique lines while sorting

Sort

Let us sort the contents of the pkg_names.txt file. It contains names R packages randomly selected from CRAN.

sort pkg_names.txt
## ASIP
## AdMit
## AnalyzeTS
## AzureStor
## AzureStor
## BIGDAWG
## BIOMASS
## BIOMASS
## BenfordTests
## BinOrdNonNor
## BioCircos
## ClimMobTools
## CombinePValue
## Eagle
## FField
## ICAOD
## MARSS
## MIAmaxent
## MIAmaxent
## MIAmaxent
## MVB
## MVTests
## MaXact
## MaxentVariableSelection
## OptimaRegion
## OxyBS
## PathSelectMP
## PropScrRand
## RJDBC
## RPyGeo
## SCRT
## SMARTp
## SPEDInstabR
## SemiParSampleSel
## SetMethods
## SmallCountRounding
## SpatioTemporal
## SphericalK
## SuppDists
## Survgini
## TIMP
## TSeriesMMA
## VineCopula
## WGScan
## WPKDE
## accept
## accept
## addhaz
## alfr
## aweek
## aweek
## bayesbio
## blink
## breakfast
## cbsem
## corclass
## crsra
## cyclocomp
## dagitty
## disparityfilter
## edfReader
## errorlocate
## expstudies
## fermicatsR
## foretell
## gLRTH
## gazepath
## generalhoslem
## geoknife
## hdnom
## hindexcalculator
## ibd
## interplot
## kfigr
## logNormReg
## ltxsparklines
## lue
## mbir
## mcmcabn
## mev
## mgcViz
## mined
## mlflow
## mongolite
## mongolite
## mvShapiroTest
## odk
## overlapping
## pAnalysis
## pls
## pmdplyr
## poisbinom
## randtests
## redcapAPI
## rgw
## rless
## rsed
## rstudioapi
## solitude
## splithalfr
## sspline
## sybilccFBA
## tailr
## tailr
## tictactoe
## viridisLite
## vqtl
## widyr
## widyr

Descending Order

Using the -r option which stands for --reverse the contents of the file can be sorted in descending/reverse order. Let us now sort the contents of the pkg_names.txt file in reverse order.

sort -r pkg_names.txt
## widyr
## widyr
## vqtl
## viridisLite
## tictactoe
## tailr
## tailr
## sybilccFBA
## sspline
## splithalfr
## solitude
## rstudioapi
## rsed
## rless
## rgw
## redcapAPI
## randtests
## poisbinom
## pmdplyr
## pls
## pAnalysis
## overlapping
## odk
## mvShapiroTest
## mongolite
## mongolite
## mlflow
## mined
## mgcViz
## mev
## mcmcabn
## mbir
## lue
## ltxsparklines
## logNormReg
## kfigr
## interplot
## ibd
## hindexcalculator
## hdnom
## geoknife
## generalhoslem
## gazepath
## gLRTH
## foretell
## fermicatsR
## expstudies
## errorlocate
## edfReader
## disparityfilter
## dagitty
## cyclocomp
## crsra
## corclass
## cbsem
## breakfast
## blink
## bayesbio
## aweek
## aweek
## alfr
## addhaz
## accept
## accept
## WPKDE
## WGScan
## VineCopula
## TSeriesMMA
## TIMP
## Survgini
## SuppDists
## SphericalK
## SpatioTemporal
## SmallCountRounding
## SetMethods
## SemiParSampleSel
## SPEDInstabR
## SMARTp
## SCRT
## RPyGeo
## RJDBC
## PropScrRand
## PathSelectMP
## OxyBS
## OptimaRegion
## MaxentVariableSelection
## MaXact
## MVTests
## MVB
## MIAmaxent
## MIAmaxent
## MIAmaxent
## MARSS
## ICAOD
## FField
## Eagle
## CombinePValue
## ClimMobTools
## BioCircos
## BinOrdNonNor
## BenfordTests
## BIOMASS
## BIOMASS
## BIGDAWG
## AzureStor
## AzureStor
## AnalyzeTS
## AdMit
## ASIP

Ignore case

To ignore case while sorting contents, use the --ignore-case option. Time to sort the pkg_names.txt file while ignoring case.

sort --ignore-case pkg_names.txt
## accept
## accept
## addhaz
## AdMit
## alfr
## AnalyzeTS
## ASIP
## aweek
## aweek
## AzureStor
## AzureStor
## bayesbio
## BenfordTests
## BIGDAWG
## BinOrdNonNor
## BioCircos
## BIOMASS
## BIOMASS
## blink
## breakfast
## cbsem
## ClimMobTools
## CombinePValue
## corclass
## crsra
## cyclocomp
## dagitty
## disparityfilter
## Eagle
## edfReader
## errorlocate
## expstudies
## fermicatsR
## FField
## foretell
## gazepath
## generalhoslem
## geoknife
## gLRTH
## hdnom
## hindexcalculator
## ibd
## ICAOD
## interplot
## kfigr
## logNormReg
## ltxsparklines
## lue
## MARSS
## MaXact
## MaxentVariableSelection
## mbir
## mcmcabn
## mev
## mgcViz
## MIAmaxent
## MIAmaxent
## MIAmaxent
## mined
## mlflow
## mongolite
## mongolite
## MVB
## mvShapiroTest
## MVTests
## odk
## OptimaRegion
## overlapping
## OxyBS
## pAnalysis
## PathSelectMP
## pls
## pmdplyr
## poisbinom
## PropScrRand
## randtests
## redcapAPI
## rgw
## RJDBC
## rless
## RPyGeo
## rsed
## rstudioapi
## SCRT
## SemiParSampleSel
## SetMethods
## SmallCountRounding
## SMARTp
## solitude
## SpatioTemporal
## SPEDInstabR
## SphericalK
## splithalfr
## sspline
## SuppDists
## Survgini
## sybilccFBA
## tailr
## tailr
## tictactoe
## TIMP
## TSeriesMMA
## VineCopula
## viridisLite
## vqtl
## WGScan
## widyr
## widyr
## WPKDE

Numeric Order

To sort numerically, use the -n option which stands for --numeric-sort. In this example, we will use a different file, package_names.txt where the package names are prefixed by random numbers between 1 and 100.

sort -n package_names.txt
## 1. cyclocomp
## 2. odk
## 3. redcapAPI
## 4. TIMP
## 5. pls
## 6. BinOrdNonNor
## 7. bayesbio
## 8. MVTests
## 9. pAnalysis
## 10. aweek
## 11. hdnom
## 12. ltxsparklines
## 13. MaXact
## 14. RJDBC
## 15. MIAmaxent
## 16. randtests
## 17. ASIP
## 18. gazepath
## 19. mcmcabn
## 20. rless
## 21. corclass
## 22. vqtl
## 23. disparityfilter
## 24. SCRT
## 25. RPyGeo
## 26. blink
## 27. gLRTH
## 28. splithalfr
## 29. sspline
## 29. sspline
## 30. logNormReg
## 31. BIGDAWG
## 31. BIGDAWG
## 32. SPEDInstabR
## 33. tailr
## 33. tailr
## 34. ibd
## 35. fermicatsR
## 36. mlflow
## 37. CombinePValue
## 38. BenfordTests
## 39. mev
## 40. MaxentVariableSelection
## 41. rstudioapi
## 42. OptimaRegion
## 43. accept
## 44. expstudies
## 45. solitude
## 45. solitude
## 46. cbsem
## 47. SMARTp
## 48. geoknife
## 49. SemiParSampleSel
## 50. mbir
## 51. interplot
## 52. ClimMobTools
## 53. MVB
## 54. OxyBS
## 55. hindexcalculator
## 56. MARSS
## 57. generalhoslem
## 58. alfr
## 59. AdMit
## 60. Eagle
## 61. PropScrRand
## 62. lue
## 63. dagitty
## 64. viridisLite
## 65. mined
## 65. mined
## 66. SuppDists
## 67. tictactoe
## 68. AzureStor
## 68. AzureStor
## 69. FField
## 70. rsed
## 70. rsed
## 71. kfigr
## 72. overlapping
## 72. overlapping
## 73. VineCopula
## 74. crsra
## 75. pmdplyr
## 76. errorlocate
## 77. SetMethods
## 78. sybilccFBA
## 79. mvShapiroTest
## 80. SpatioTemporal
## 81. mgcViz
## 82. breakfast
## 83. WPKDE
## 84. BIOMASS
## 85. edfReader
## 86. mongolite
## 87. WGScan
## 88. SphericalK
## 89. foretell
## 90. widyr
## 91. rgw
## 92. BioCircos
## 93. PathSelectMP
## 94. ICAOD
## 95. TSeriesMMA
## 96. poisbinom
## 97. AnalyzeTS
## 98. SmallCountRounding
## 99. Survgini
## 100. addhaz

Preserve Only Unique Lines

The -u option which stands for --unique will preserve only unique lines while sorting the contents of the file. In the below example, we remove all duplicate lines from the pkg_names.txt while sorting.

sort -u pkg_names.txt
## ASIP
## AdMit
## AnalyzeTS
## AzureStor
## BIGDAWG
## BIOMASS
## BenfordTests
## BinOrdNonNor
## BioCircos
## ClimMobTools
## CombinePValue
## Eagle
## FField
## ICAOD
## MARSS
## MIAmaxent
## MVB
## MVTests
## MaXact
## MaxentVariableSelection
## OptimaRegion
## OxyBS
## PathSelectMP
## PropScrRand
## RJDBC
## RPyGeo
## SCRT
## SMARTp
## SPEDInstabR
## SemiParSampleSel
## SetMethods
## SmallCountRounding
## SpatioTemporal
## SphericalK
## SuppDists
## Survgini
## TIMP
## TSeriesMMA
## VineCopula
## WGScan
## WPKDE
## accept
## accept
## addhaz
## alfr
## aweek
## bayesbio
## blink
## breakfast
## cbsem
## corclass
## crsra
## cyclocomp
## dagitty
## disparityfilter
## edfReader
## errorlocate
## expstudies
## fermicatsR
## foretell
## gLRTH
## gazepath
## generalhoslem
## geoknife
## hdnom
## hindexcalculator
## ibd
## interplot
## kfigr
## logNormReg
## ltxsparklines
## lue
## mbir
## mcmcabn
## mev
## mgcViz
## mined
## mlflow
## mongolite
## mvShapiroTest
## odk
## overlapping
## pAnalysis
## pls
## pmdplyr
## poisbinom
## randtests
## redcapAPI
## rgw
## rless
## rsed
## rstudioapi
## solitude
## splithalfr
## sspline
## sybilccFBA
## tailr
## tictactoe
## viridisLite
## vqtl
## widyr

Word Count

wc will print newline, word, and byte counts for file(s). If more than one file is specified, it will also print total line.

Count words, bytes and lines

wc release_names.txt
##  30  73 546 release_names.txt

Count lines in a file

wc -l release_names.txt
## 30 release_names.txt

Count words in a file

wc -w release_names.txt
## 73 release_names.txt

Count characters(bytes) in a file

wc -c release_names.txt
## 546 release_names.txt

youtube ad

Search & Regular Expressions

In this section, we will explore commands that will

  • search for a given string in a file
  • find files using names
  • and search for binary executable files
Command Description
grep Search for a given string in a file
find Find files using filenames
which Search for binary executable files

grep

The grep command is used for pattern matching. Along with additional options, it can be used to

  • match pattern in input text
  • ignore case
  • search recursively for an exact string
  • print filename and line number for each match
  • invert match for excluding specific strings

grep processes text line by line, and prints any lines which match a specified pattern. grep, which stands for global regular expression print is a powerful tool for matching a regular expression against text in a file, multiple files, or a stream of input.

Command Description
grep Matches pattern in input text
grep -i Ignore case
grep -RI Search recursively for an exact string
grep -E Use extended regular expression
grep -Hn Print file name & corresponding line number for each match
grep -v Invert match for excluding specific strings

Match Pattern in Input Text

Using grep let us search for packages that inlcude the letter R in their names.

grep R package_names.txt
## 14. RJDBC
## 30. logNormReg
## 27. gLRTH
## 35. fermicatsR
## 42. OptimaRegion
## 61. PropScrRand
## 25. RPyGeo
## 47. SMARTp
## 24. SCRT
## 56. MARSS
## 85. edfReader
## 32. SPEDInstabR
## 98. SmallCountRounding

Ignore Case

In the previous case, grep returned only those packages whose name included R but not r i.e. it did not ignore the case of the letter. Using the -i option, we will now search while ignoring the case of the letter.

grep -i R package_names.txt
## 14. RJDBC
## 58. alfr
## 64. viridisLite
## 99. Survgini
## 30. logNormReg
## 27. gLRTH
## 71. kfigr
## 72. overlapping
## 90. widyr
## 33. tailr
## 40. MaxentVariableSelection
## 33. tailr
## 72. overlapping
## 16. randtests
## 12. ltxsparklines
## 91. rgw
## 35. fermicatsR
## 21. corclass
## 68. AzureStor
## 42. OptimaRegion
## 61. PropScrRand
## 74. crsra
## 80. SpatioTemporal
## 23. disparityfilter
## 49. SemiParSampleSel
## 76. errorlocate
## 88. SphericalK
## 28. splithalfr
## 89. foretell
## 25. RPyGeo
## 50. mbir
## 51. interplot
## 6. BinOrdNonNor
## 47. SMARTp
## 38. BenfordTests
## 79. mvShapiroTest
## 92. BioCircos
## 55. hindexcalculator
## 41. rstudioapi
## 57. generalhoslem
## 24. SCRT
## 95. TSeriesMMA
## 82. breakfast
## 56. MARSS
## 70. rsed
## 68. AzureStor
## 85. edfReader
## 20. rless
## 75. pmdplyr
## 32. SPEDInstabR
## 3. redcapAPI
## 70. rsed
## 98. SmallCountRounding

Highlight

The --color option will highlight the matched strings.

grep -i --color R package_names.txt
## 14. RJDBC
## 58. alfr
## 64. viridisLite
## 99. Survgini
## 30. logNormReg
## 27. gLRTH
## 71. kfigr
## 72. overlapping
## 90. widyr
## 33. tailr
## 40. MaxentVariableSelection
## 33. tailr
## 72. overlapping
## 16. randtests
## 12. ltxsparklines
## 91. rgw
## 35. fermicatsR
## 21. corclass
## 68. AzureStor
## 42. OptimaRegion
## 61. PropScrRand
## 74. crsra
## 80. SpatioTemporal
## 23. disparityfilter
## 49. SemiParSampleSel
## 76. errorlocate
## 88. SphericalK
## 28. splithalfr
## 89. foretell
## 25. RPyGeo
## 50. mbir
## 51. interplot
## 6. BinOrdNonNor
## 47. SMARTp
## 38. BenfordTests
## 79. mvShapiroTest
## 92. BioCircos
## 55. hindexcalculator
## 41. rstudioapi
## 57. generalhoslem
## 24. SCRT
## 95. TSeriesMMA
## 82. breakfast
## 56. MARSS
## 70. rsed
## 68. AzureStor
## 85. edfReader
## 20. rless
## 75. pmdplyr
## 32. SPEDInstabR
## 3. redcapAPI
## 70. rsed
## 98. SmallCountRounding

Invert Match

Use the -v option to select non-matching lines. In the below example, we search for packages whose name does not include R while ignoring the case.

grep -v -i R package_names.txt
## 36. mlflow
## 10. aweek
## 31. BIGDAWG
## 22. vqtl
## 29. sspline
## 39. mev
## 66. SuppDists
## 15. MIAmaxent
## 31. BIGDAWG
## 29. sspline
## 60. Eagle
## 83. WPKDE
## 11. hdnom
## 26. blink
## 18. gazepath
## 52. ClimMobTools
## 44. expstudies
## 65. mined
## 81. mgcViz
## 45. solitude
## 9. pAnalysis
## 65. mined
## 94. ICAOD
## 48. geoknife
## 45. solitude
## 67. tictactoe
## 46. cbsem
## 93. PathSelectMP
## 96. poisbinom
## 17. ASIP
## 5. pls
## 84. BIOMASS
## 59. AdMit
## 77. SetMethods
## 53. MVB
## 2. odk
## 86. mongolite
## 4. TIMP
## 97. AnalyzeTS
## 87. WGScan
## 63. dagitty
## 69. FField
## 13. MaXact
## 73. VineCopula
## 7. bayesbio
## 34. ibd
## 8. MVTests
## 19. mcmcabn
## 43. accept
## 78. sybilccFBA
## 62. lue
## 100. addhaz
## 37. CombinePValue
## 1. cyclocomp
## 54. OxyBS

find

The find command can be used for searching files and directories. Using additional options, we can

  • search files by extension type
  • ignore case while searching files/directories

find is a powerful tool for working with the files. It can be used on its own to locate files, or in conjunction with other programs to perform operations on those files.

Command Description
find Find files or directories under the given directory; recursively
find -name '*.txt' Find files by extension
find -type d -iname Find directories matching a given name, in case-insensitive mode
find -type d -name Find directories matching a given name, in case-sensitive mode

Search Recursively

Let us use find to search for the file release_names.txt recursively. The -name option is used to specify the name of the file we are searching.

find -name release_names.txt
## ./release_names.txt
## ./r_releases/release_names.txt

There are two files with the name release_names.txt present in the current working directory and in r_releases directory.

Search by Extension

Let us search for all files with .txt extension in the r_releases folder.

find r_releases -name '*.txt'
## r_releases/release_names.txt
## r_releases/release_names_2.txt
## r_releases/release_names_3.txt

There are 3 files with the .txt extension in r_releases folder.

Case-insensitive Mode

Search for all folders with the name R or r. Here we use the -iname option to ignore case while searching. The -type option is used to specify whether we are searching for files or folders. Since we are searching for folder/directory, we use it along with d i.e. directory to indicate that we are searching for directories and not files.

find -type d -iname R
## ./mypackage/R
## ./r

Case-sensitive Mode

Search for all folders with the name r. It should exclude any folder with the name R.

find -type d -name r
## ./r

Data Transfer & Network

In this section, we will explore commands that will allow us to download files from the internet.

Command Description
wget Download files from the web
curl Transfer data from or to a server
hostname Name of the current host
ping Ping a remote host
nslookup Name server details

We have not executed the commands in this ebook as downloading multiple files from the internet will take a lot of time or result in errors but we have checked all the commands offline to ensure that they work.

wget

The wget command will download contents of a URL and files from the internet. Using additional options, we can

  • download contents/files to a file
  • continue incomplete downloads
  • download multiple files
  • limit download speed and number of retries
Command Description
wget url Download contents of a url
wget -o file url Download contents of url to a file
wget -c Continue an incomplete download
wget -P folder_name -i urls.txt Download all urls stored in a text file to a specific directory
wget --limit-rate Limit download speed
wget --tries Limit number of retries
wget --quiet Turn off output
wget --no-verbose Print basic information
wget --progress-dot Change progress bar type to dot
wget --timestamping Check if the timestamp of the file has changed before downloading
wget --wait Wait between retrievals

Download URL

Let us first use wget to download contents of a URL. Note, we are not downloading file as such but just the content of the URL. We will use the URL of the home page of R project.

wget https://www.r-project.org/

If you look at the list of files, you can see a new file, index.html which we just downloaded using wget. Downloading contents this way will lead to confusion if we are dealing with multiple URLs. Let us learn to save the contents to a file (we can specify the name of the file which should help avoid confusion.)

Specify Filename

In this example, we download contents from the same URL and in addition specify the name of the file in which the content must be saved. Here we save it in a new file, rhomepage.html using the -o option followed by the filename.

wget -o rhomepage.html https://www.r-project.org/

Download File

How about downloading a file instead of a URL? In this example, we will download a logfile from the RStudio CRAN mirror. It contains the details of R downloads and individual package downloads. If you are a package developer and would want to know the countries in which your packages are downloaded, you will find this useful. We will download the file for 29th September and save it as sep_29.csv.gz.

wget -o sep_29.csv.gz http://cran-logs.rstudio.com/2019/2019-09-29.csv.gz

Download Multiple URLs

How do we download multiple URLs? One way is to specify the URLs one after the other separated by a space or save all URLs in a file and read them one by one. In the below example, we have saved multiple URLs in the file urls.txt.

cat urls.txt
## http://cran-logs.rstudio.com/2019/2019-09-26.csv.gz
## http://cran-logs.rstudio.com/2019/2019-09-27.csv.gz
## http://cran-logs.rstudio.com/2019/2019-09-28.csv.gz

We will download all the above URLs and save them in a new folder downloads. The -i indicates that the URLs must be read from a file (local or external). The -P option allows us to specify the directory into which all the files will be downloaded.

wget -P downloads -i urls.txt

Quiet

The --quiet option will turn off wget output. It will not show any of the following details:

  • name of the file being saved
  • file size
  • download speed
  • eta etc.
wget –-quiet http://cran-logs.rstudio.com/2019/2019-10-06.csv.gz

No Verbose

Using the -nv or --no-verbose option, we can turn off verbose without being completely quiet (as we did in the previous example). Any error messages and basic information will still be printed.

wget –-no-verbose http://cran-logs.rstudio.com/2019/2019-10-13.csv.gz

Check Timestamp

Let us say we have already downloaded a file from a URL. The file is updated from time to time and we intend to keep the local copy updated as well. Using the --timestamping option, the local file will have timestamp matching the remote file; if the remote file is not newer (not updated), no download will occur i.e. if the timestamp of the remote file has not changed it will not be downloaded. This is very useful in case of large files where you do not want to download them unless they have been updated.

wget –-timestamping http://cran-logs.rstudio.com/2019/2019-10-13.csv.gz

curl

The curl command will transfer data from or to a server. We will only look at downloading files from the internet.

Command Description
curl url Download contents of a url
curl url -o file Download contents of url to a file
curl url &gt; file Download contents of url to a file
curl -s Download in silent or quiet mode

Download URL

Let us download the home page of the R project using curl.

curl https://www.r-project.org/

Specify File

Let us download another log file from the RStudio CRAN mirror and save it into a file using the -o option.

curl http://cran-logs.rstudio.com/2019/2019-09-08.csv.gz -o sept_08.csv.gz

Another way to save a downloaded file is to use > followed by the name of the file as shown in the below example.

curl http://cran-logs.rstudio.com/2019/2019-09-01.csv.gz > sep_01.csv.gz

Download Silently

The -s option will allow you to download files silently. It will mute curl and will not display progress meter or error messages.

curl http://cran-logs.rstudio.com/2019/2019-09-01.csv.gz -o sept_01.csv.gz -s

R Functions

In R, we can use download.file() to download files from the internet. The following packages offer functionalities that you will find useful.

Command R
wget download.file()
curl curl::curl_download()
hostname R.utils::getHostname.System()
ping pingr::ping()
nslookup curl::nslookup()

sudo

sudo Super User DO is a prefix of commands that only superuser or root users are allowed to run. It is similar to run as administrator option in Windows. It is used to install, update and remove software. We will use it in the next section to install & update packages. If you are using RStudio Cloud, you will not be able to run sudo (users do not have root privileges).

Command Description
dpkg --list List installed packages
sudo apt-get update Update packages
sudo apt-get install Install packages
sudo apt-get remove Remove packages (retain configuration, plugins and settings
sudo apt-get purge Remove packages including personalized settings
sudo apt-get autoremove Remove any dependencies no longer in use

File Compression

tar

The tar command is used for file compression. It works with both tar and tar.gz extensions. It is used to

  • list files
  • extract files
  • create archives
  • append file to existing archives

tar creates, maintains, modifies, and extracts files that are archived in the tar format. Tar stands for tape archive and is an archiving file format.

Command Description
tar tvf List an archive
tar tvfz List a gzipped archive
tar xvf Extract an archive
tar xvfz Extract a gzipped archive
tar cvf Create an uncompressed tar archive
tar cvfz Create a tar gzipped archive
tar rvf Add a file to an existing archive
tar rvfz Add a file to an existing gzipped archive

We will use different options along with the tar command for listing, extracting, creating and adding files. The vf (v stands for verbosely show .tar file progress and f stands for file name type of the archive file) option is common for all the above operations while the following are specific.

  • t for listing
  • x for extracting
  • c for creating
  • r for adding files

While dealing with tar.gz archives we will use z in addition to vf and the above options.

List

Let us list all the files & folders in release_names.tar. As mentioned above. to list the files in the archive, we use the t option.

tar -tvf release_names.tar 
## -rwxrwxrwx aravind/aravind 546 2019-09-16 15:59 release_names.txt
## -rwxrwxrwx aravind/aravind  65 2019-09-16 15:58 release_names_18.txt
## -rwxrwxrwx aravind/aravind  53 2019-09-16 15:59 release_names_19.txt

Extract

Let us extract files from release_names.tar using the x option in addition to vf.

tar -xvf release_names.tar 
ls
## release_names.txt
## release_names_18.txt
## release_names_19.txt
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject3
## myproject4
## package_names.txt
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_18_19.txt
## release_names_19.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Add

To add a file to an existing archive, use the r option. Let us add release_names_18.txt and release_names_19.txt to the archive we created in the previous step.

tar -rvf release_names.tar release_names_18.txt release_names_19.txt
## release_names_18.txt
## release_names_19.txt

Create

Using the c option we can create tar archives. In the below example, we are using a single file but you can specify multiple files and folders as well.

tar -cvf pkg_names.tar pkg_names.txt
## pkg_names.txt

gzip

Command Description
gzip Compress a file
gzip -d Decompress a file
gzip -c Compress a file and specify the output file name
zip -r Compress a directory
zip Add files to an existing zip file
unzip Extract files from a zip files
unzip -d Extract files from a zip file and specify the output file name
unzip -l List contents of a zip file

gzip, gunzip, and zcat commands are used to compress or expand files in the GNU GZIP format i.e. files with .gz extension

Compress

Let us compress release_names.txt file using gzip.

gzip release_names.txt
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject3
## myproject4
## package_names.txt
## pkg_names.tar
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt.gz
## release_names_18.txt
## release_names_18_19.txt
## release_names_19.txt
## sept_15.csv.gz
## urls.txt
## zip_example.zip

Decompress

Use the -d option with gzip to decompress a file. In the below example, we decompress the sept_15.csv.gz file (downloaded using wget or curl earlier). You can also use gunzip for the same result.

gzip -d sept_15.csv.gz
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject3
## myproject4
## package_names.txt
## pkg_names.tar
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_18_19.txt
## release_names_19.txt
## sept_15.csv
## urls.txt
## zip_example.zip

Specify Filename

Use -c and > to specify a different file name while compressing using gzip. In the below example, gzip will create releases.txt.gz instead of release_names.txt.gz.

gzip -c release_names.txt > releases.txt.gz
ls
## analysis.R
## bash.R
## bash.sh
## imports_blorr.txt
## imports_olsrr.txt
## lorem-ipsum.txt
## main_project.zip
## myfiles
## mypackage
## myproject
## myproject3
## myproject4
## package_names.txt
## pkg_names.tar
## pkg_names.txt
## r
## r2
## r_releases
## release_names.tar
## release_names.tar.gz
## release_names.txt
## release_names_18.txt
## release_names_18_19.txt
## release_names_19.txt
## releases.txt.gz
## sept_15.csv
## urls.txt
## zip_example.zip

zip & unzip

zip creates ZIP archives while unzip lists and extracts compressed files in a ZIP archive.

List

Let us list all the files and folders in main_project.zip() using unzip and the -l option.

unzip -l main_project.zip
## Archive:  main_project.zip
##   Length      Date    Time    Name
## ---------  ---------- -----   ----
##         0  2019-09-23 18:07   myproject/
##         0  2019-09-20 14:02   myproject/.gitignore
##         0  2019-09-23 18:07   myproject/data/
##         0  2019-09-20 14:02   myproject/data/processed/
##         0  2019-09-20 14:02   myproject/data/raw/
##         0  2019-09-20 14:02   myproject/output/
##         0  2019-09-20 14:02   myproject/README.md
##        13  2019-09-20 14:02   myproject/run_analysis.R
##         0  2019-09-20 14:02   myproject/src/
##         0  2019-09-23 18:07   mypackage/
##         0  2019-09-20 14:11   mypackage/.gitignore
##         0  2019-09-20 14:11   mypackage/.Rbuildignore
##         0  2019-09-20 14:10   mypackage/data/
##         0  2019-09-20 14:11   mypackage/DESCRIPTION
##         0  2019-09-20 14:10   mypackage/docs/
##         0  2019-09-20 14:11   mypackage/LICENSE
##         0  2019-09-20 14:10   mypackage/man/
##         0  2019-09-20 14:11   mypackage/NAMESPACE
##         0  2019-09-20 14:11   mypackage/NEWS.md
##         0  2019-09-20 14:10   mypackage/R/
##         0  2019-09-20 14:11   mypackage/README.md
##         0  2019-09-20 14:11   mypackage/src/
##         0  2019-09-20 14:10   mypackage/tests/
##         0  2019-09-20 14:10   mypackage/vignettes/
##         0  2019-09-23 18:07   myfiles/
##        12  2019-09-20 15:30   myfiles/analysis.R
##         7  2019-09-20 15:31   myfiles/NEWS.md
##         9  2019-09-20 15:31   myfiles/README.md
##       546  2019-09-20 15:29   myfiles/release_names.txt
##        65  2019-09-20 15:29   myfiles/release_names_18.txt
##        53  2019-09-20 15:30   myfiles/release_names_19.txt
##        12  2019-09-20 15:30   myfiles/visualization.R
##     15333  2019-10-01 16:58   bash.sh
##         0  2019-09-16 12:42   r/
## ---------                     -------
##     16050                     34 files

Extract

Using unzip, let us now extract files and folders from zip_example.zip.

unzip zip_example.zip
## Archive:  zip_example.zip
##    creating: zip_example/
##   inflating: zip_example/bash.sh     
##   inflating: zip_example/pkg_names.txt

Using the -d option, we can extract the contents of zip_example.zip to a specific folder. In the below example, we extract it to a new folder examples.

unzip zip_example.zip –d myexamples
## [1] "Archive:  zip_example.zip"                        
## [2] "   creating: examples/zip_example/"               
## [3] "  inflating: examples/zip_example/bash.sh  "      
## [4] "  inflating: examples/zip_example/pkg_names.txt  "

Compress

Use the -r option along with zip to create a ZIP archive. In the below example, we create a ZIP archive of myproject folder.

zip -r myproject.zip myproject
ls
##   adding: myproject/ (stored 0%)
##   adding: myproject/.gitignore (stored 0%)
##   adding: myproject/data/ (stored 0%)
##   adding: myproject/data/processed/ (stored 0%)
##   adding: myproject/data/raw/ (stored 0%)
##   adding: myproject/output/ (stored 0%)
##   adding: myproject/README.md (stored 0%)
##   adding: myproject/run_analysis.R (stored 0%)
##   adding: myproject/src/ (stored 0%)

We can compress multiple directories using zip. The names of the directories must be separated by a space as shown in the below example where we compress myproject and mypackage into a single ZIP archive.

zip -r packproj.zip myproject mypackage
ls
##   adding: myproject/ (stored 0%)
##   adding: myproject/.gitignore (stored 0%)
##   adding: myproject/data/ (stored 0%)
##   adding: myproject/data/processed/ (stored 0%)
##   adding: myproject/data/raw/ (stored 0%)
##   adding: myproject/output/ (stored 0%)
##   adding: myproject/README.md (stored 0%)
##   adding: myproject/run_analysis.R (stored 0%)
##   adding: myproject/src/ (stored 0%)
##   adding: mypackage/ (stored 0%)
##   adding: mypackage/.gitignore (stored 0%)
##   adding: mypackage/.Rbuildignore (stored 0%)
##   adding: mypackage/data/ (stored 0%)
##   adding: mypackage/DESCRIPTION (stored 0%)
##   adding: mypackage/docs/ (stored 0%)
##   adding: mypackage/LICENSE (stored 0%)
##   adding: mypackage/man/ (stored 0%)
##   adding: mypackage/NAMESPACE (stored 0%)
##   adding: mypackage/NEWS.md (stored 0%)
##   adding: mypackage/R/ (stored 0%)
##   adding: mypackage/README.md (stored 0%)
##   adding: mypackage/src/ (stored 0%)
##   adding: mypackage/tests/ (stored 0%)
##   adding: mypackage/vignettes/ (stored 0%)

Add

To add a new file/folder to an existing archive, specify the name of the archive followed by the name of the file or the folder. In the below example, we add the bash.sh file to the myproject.zip archive created in a previous step.

zip myproject.zip bash.sh
##   adding: bash.sh (deflated 78%)

R Functions

tar & tar.gz

In R, we can use the tar() and untar() functions from the utils package to handle .tar and .tar.gz archives.

Command R
tar tvf utils::untar('archive.tar', list = TRUE)
tar tvfz utils::untar('archive.tar.gz', list = TRUE)
tar xvf utils::untar('archive.tar')
tar xvfz utils::untar('archive.tar.gz')
tar cvf utils::tar('archive.tar')
tar cvfz utils::tar('archive.tar', compression = 'gzip')

zip & gzip

The zip package has the functionalities to handle ZIP archives. The tar() and untar() functions from the utils package can handle GZIP archives.

Command R
gzip utils::tar(compression = 'gzip' / R.utils::gzip()
gzip -d utils::untar() / R.utils::gunzip()
gzip -c utils::untar(exdir = filename)
zip -r zip::zip()
zip zip::zipr_append()
unzip zip::unzip()
unzip -d zip::unzip(exdir = dir_name)
unzip -l zip::zip_list()

System Info

In this section, we will explore commands that will allow us to

  • display information about the system
  • display memory usage information
  • display file system disk space usage
  • exit the terminal
  • run commands a superuser
  • shutdown the system
Command Description
uname Display important information about the system
free Display free, used, swap memory in the system
df Display file system disk space usage
exit Exit the terminal
sudo Run command as super user
shutdown Shutdown the system

uname

The uname command is used to view important information about the system. Using additional options, we can

  • print details about operating system
  • hardware & software related information
Command Description
uname Print details about the current machine and the operating system running on it
uname -mp Hardware related information; machine & processor
uname -srv Software related information; operating system, release number and version
uname -n Nodename of the system
uname -a Print all available information system

Display free, used, swap memory in the system

free
##               total        used        free      shared  buff/cache   available
## Mem:        3621900     1815864     1576684       17720      229352     1672304
## Swap:      11010048      260640    10749408

Display file system disk space usage

df
## Filesystem     1K-blocks      Used Available Use% Mounted on
## rootfs         188482144 142470276  46011868  76% /
## none           188482144 142470276  46011868  76% /dev
## none           188482144 142470276  46011868  76% /run
## none           188482144 142470276  46011868  76% /run/lock
## none           188482144 142470276  46011868  76% /run/shm
## none           188482144 142470276  46011868  76% /run/user
## cgroup         188482144 142470276  46011868  76% /sys/fs/cgroup
## C:\            188482144 142470276  46011868  76% /mnt/c
## D:\             18660348  17154308   1506040  92% /mnt/d
## F:\              3196924    231756   2965168   8% /mnt/f
## G:\             86383612  24561220  61822392  29% /mnt/g
## H:\             86383612  14755988  71627624  18% /mnt/h
## J:\             83185660  18797916  64387744  23% /mnt/j

Others

In this section, let us look at a few other useful commands that will allow us to

  • see how long a command takes to execute
  • delay activity
  • display and clear command history list
Command Description
time See how long a command takes to execute
sleep Delay activity in seconds
sleep 1m Delay activity in minutes
sleep 1h Delay activity in hours
history Display command history list with line numbers
history -c Clear the command history list

Funny Commands

Below are a few funny commands for you to try out. Use sudo apt-get install to install fortune and banner before trying them.

Command Description
fortune Poignant, inspirational & silly phrases
yes Output a string repeatedly until killed
banner ASCII banner
rev Reverse each character

R Functions

In R, we can use Sys.sleep() to delay activity and history() to view command history.

Command R
sleep Sys.sleep()
history history()

packages ad

Execute Commands from R

Now, let us turn our attention to executing commands from R using system2(). Here we will focus on the following

  • execute a command without arguments
  • execute commands with arguments
  • redirect output

Let us try to execute a command without any additional arguments. We will execute the ls command to list all files and directories. Use system2() and specify the command using the command argument. Whenever you are trying to execute a command from R, the first argument or input should be the command and it must be enclosed in quotes.

system2(command = "ls")
##   [1] "2017-02-05-variables.Rmd"                                       
##   [2] "2017-02-05-variables.html"                                      
##   [3] "2017-02-17-data-types-in-r.Rmd"                                 
##   [4] "2017-02-17-data-types-in-r.html"                                
##   [5] "2017-03-01-getting-help-in-r.html"                              
##   [6] "2017-03-13-beginners-guide-to-r-package-ecosystem.Rmd"          
##   [7] "2017-03-13-beginners-guide-to-r-package-ecosystem.html"         
##   [8] "2017-03-25-vectors.Rmd"                                         
##   [9] "2017-03-25-vectors.html"                                        
##  [10] "2017-03-29-vectors-part-2.Rmd"                                  
##  [11] "2017-03-29-vectors-part-2.html"                                 
##  [12] "2017-04-03-vectors-part-3.Rmd"                                  
##  [13] "2017-04-03-vectors-part-3.html"                                 
##  [14] "2017-04-06-matrix.Rmd"                                          
##  [15] "2017-04-06-matrix.html"                                         
##  [16] "2017-04-12-matrix-part-2.Rmd"                                   
##  [17] "2017-04-12-matrix-part-2.html"                                  
##  [18] "2017-04-18-lists.Rmd"                                           
##  [19] "2017-04-18-lists.html"                                          
##  [20] "2017-04-30-factors.Rmd"                                         
##  [21] "2017-04-30-factors.html"                                        
##  [22] "2017-05-12-dataframes.Rmd"                                      
##  [23] "2017-05-12-dataframes.html"                                     
##  [24] "2017-05-24-data-visualization-with-r-introduction.Rmd"          
##  [25] "2017-05-24-data-visualization-with-r-introduction.html"         
##  [26] "2017-06-05-data-visualization-with-r-title-and-axis-labels.Rmd" 
##  [27] "2017-06-05-data-visualization-with-r-title-and-axis-labels.html"
##  [28] "2017-06-17-data-visualization-with-r-scatter-plots.Rmd"         
##  [29] "2017-06-17-data-visualization-with-r-scatter-plots.html"        
##  [30] "2017-06-29-data-visualization-with-r-line-graphs.Rmd"           
##  [31] "2017-06-29-data-visualization-with-r-line-graphs.html"          
##  [32] "2017-07-11-data-visualization-with-r-bar-plots.Rmd"             
##  [33] "2017-07-11-data-visualization-with-r-bar-plots.html"            
##  [34] "2017-07-23-data-visualization-with-r-box-plots.Rmd"             
##  [35] "2017-07-23-data-visualization-with-r-box-plots.html"            
##  [36] "2017-08-04-data-visualization-with-r-histogram.Rmd"             
##  [37] "2017-08-04-data-visualization-with-r-histogram.html"            
##  [38] "2017-08-16-data-visualization-with-r-legends.Rmd"               
##  [39] "2017-08-16-data-visualization-with-r-legends.html"              
##  [40] "2017-08-28-data-visualization-with-r-text-annotations.Rmd"      
##  [41] "2017-08-28-data-visualization-with-r-text-annotations.html"     
##  [42] "2017-09-09-data-visualization-with-r-combining-plots.Rmd"       
##  [43] "2017-09-09-data-visualization-with-r-combining-plots.html"      
##  [44] "2017-10-03-ggplot2-quick-tour.Rmd"                              
##  [45] "2017-10-03-ggplot2-quick-tour.html"                             
##  [46] "2017-10-15-ggplot2-introduction-to-geoms.Rmd"                   
##  [47] "2017-10-15-ggplot2-introduction-to-geoms.html"                  
##  [48] "2017-10-27-ggplot2-introduction-to-aesthetics.Rmd"              
##  [49] "2017-10-27-ggplot2-introduction-to-aesthetics.html"             
##  [50] "2017-11-08-ggplot2-axis-plot-labels.Rmd"                        
##  [51] "2017-11-08-ggplot2-axis-plot-labels.html"                       
##  [52] "2017-11-20-ggplot2-text-annotations.Rmd"                        
##  [53] "2017-11-20-ggplot2-text-annotations.html"                       
##  [54] "2017-12-02-ggplot2-scatter-plots.Rmd"                           
##  [55] "2017-12-02-ggplot2-scatter-plots.html"                          
##  [56] "2017-12-14-ggplot2-line-graphs.Rmd"                             
##  [57] "2017-12-14-ggplot2-line-graphs.html"                            
##  [58] "2017-12-26-ggplot2-bar-plots.Rmd"                               
##  [59] "2017-12-26-ggplot2-bar-plots.html"                              
##  [60] "2018-01-07-ggplot2-box-plots.Rmd"                               
##  [61] "2018-01-07-ggplot2-box-plots.html"                              
##  [62] "2018-01-19-ggplot2-histogram.Rmd"                               
##  [63] "2018-01-19-ggplot2-histogram.html"                              
##  [64] "2018-01-31-ggplot2-guides-axes.Rmd"                             
##  [65] "2018-01-31-ggplot2-guides-axes.html"                            
##  [66] "2018-02-12-ggplot2-guides-legends.Rmd"                          
##  [67] "2018-02-12-ggplot2-guides-legends.html"                         
##  [68] "2018-02-24-guides-legends-part-2.Rmd"                           
##  [69] "2018-02-24-guides-legends-part-2.html"                          
##  [70] "2018-03-08-legend-part-3.Rmd"                                   
##  [71] "2018-03-08-legend-part-3.html"                                  
##  [72] "2018-03-20-legend-part-4.Rmd"                                   
##  [73] "2018-03-20-legend-part-4.html"                                  
##  [74] "2018-04-01-legend-part-5.Rmd"                                   
##  [75] "2018-04-01-legend-part-5.html"                                  
##  [76] "2018-04-13-legend-part-6.Rmd"                                   
##  [77] "2018-04-13-legend-part-6.html"                                  
##  [78] "2018-04-25-ggplot2-facets-combine-multiple-plots.Rmd"           
##  [79] "2018-04-25-ggplot2-facets-combine-multiple-plots.html"          
##  [80] "2018-05-07-ggplot2-themes.Rmd"                                  
##  [81] "2018-05-07-ggplot2-themes.html"                                 
##  [82] "2018-07-30-importing-data-into-r-part-1.Rmd"                    
##  [83] "2018-07-30-importing-data-into-r-part-1.html"                   
##  [84] "2018-08-11-importing-data-into-r-part-2.Rmd"                    
##  [85] "2018-08-11-importing-data-into-r-part-2.html"                   
##  [86] "2018-08-23-data-wrangling-with-dplyr-part-1.Rmd"                
##  [87] "2018-08-23-data-wrangling-with-dplyr-part-1.html"               
##  [88] "2018-09-04-data-wrangling-with-dplyr-part-2.Rmd"                
##  [89] "2018-09-04-data-wrangling-with-dplyr-part-2.html"               
##  [90] "2018-09-16-data-wrangling-with-dplyr-part-3.Rmd"                
##  [91] "2018-09-16-data-wrangling-with-dplyr-part-3.html"               
##  [92] "2018-09-28-introduction-to-tibbles.Rmd"                         
##  [93] "2018-09-28-introduction-to-tibbles.html"                        
##  [94] "2018-10-10-readable-code-with-pipes.Rmd"                        
##  [95] "2018-10-10-readable-code-with-pipes.html"                       
##  [96] "2018-10-22-hacking-strings-with-stringr.Rmd"                    
##  [97] "2018-10-22-hacking-strings-with-stringr.html"                   
##  [98] "2018-11-03-working-with-dates-in-r.Rmd"                         
##  [99] "2018-11-03-working-with-dates-in-r.html"                        
## [100] "2018-11-15-working-with-categorical-data-using-forcats.Rmd"     
## [101] "2018-11-15-working-with-categorical-data-using-forcats.html"    
## [102] "2018-11-27-quick-guide-r-sqlite.Rmd"                            
## [103] "2018-11-27-quick-guide-r-sqlite.html"                           
## [104] "2018-12-09-data-wrangling-with-dbplyr.Rmd"                      
## [105] "2018-12-09-data-wrangling-with-dbplyr.html"                     
## [106] "2018-12-21-sql-for-data-science.Rmd"                            
## [107] "2018-12-21-sql-for-data-science.html"                           
## [108] "2019-01-02-sql-for-data-science-part-2.Rmd"                     
## [109] "2019-01-02-sql-for-data-science-part-2.html"                    
## [110] "2019-02-08-introducing-olsrr.Rmd"                               
## [111] "2019-02-08-introducing-olsrr.html"                              
## [112] "2019-02-12-introducing-rfm.Rmd"                                 
## [113] "2019-02-12-introducing-rfm.html"                                
## [114] "2019-02-19-introducing-descriptr.Rmd"                           
## [115] "2019-02-19-introducing-descriptr.html"                          
## [116] "2019-02-20-introducing-descriptr.Rmd"                           
## [117] "2019-02-20-introducing-descriptr.html"                          
## [118] "2019-02-26-introducing-blorr.Rmd"                               
## [119] "2019-02-26-introducing-blorr.html"                              
## [120] "2019-03-05-getting-help-in-r.Rmd"                               
## [121] "2019-03-05-getting-help-in-r.html"                              
## [122] "2019-03-12-introducing-rbin.Rmd"                                
## [123] "2019-03-12-introducing-rbin.html"                               
## [124] "2019-03-14-introducing-vistributions.Rmd"                       
## [125] "2019-03-14-introducing-vistributions.html"                      
## [126] "2019-04-01-shiny-apps.Rmd"                                      
## [127] "2019-04-01-shiny-apps.html"                                     
## [128] "2019-04-11-web-scraping.Rmd"                                    
## [129] "2019-04-11-web-scraping.html"                                   
## [130] "2019-04-13-web-scraping-note.Rmd"                               
## [131] "2019-04-13-web-scraping-note.html"                              
## [132] "2019-05-02-mba.Rmd"                                             
## [133] "2019-05-02-mba.html"                                            
## [134] "2019-05-02-mba_files"                                           
## [135] "2019-05-27-regex.Rmd"                                           
## [136] "2019-05-27-regex.html"                                          
## [137] "2019-07-05-pkginfo.Rmd"                                         
## [138] "2019-07-05-pkginfo.html"                                        
## [139] "2019-07-22-customer-segmentation-using-rfm-analysis.Rmd"        
## [140] "2019-07-22-customer-segmentation-using-rfm-analysis.html"       
## [141] "2019-07-22-customer-segmentation-using-rfm-analysis_files"      
## [142] "2019-08-08-working-with-databases-using-r.Rmd"                  
## [143] "2019-08-08-working-with-databases-using-r.html"                 
## [144] "2019-08-08-working-with-databases-using-r_files"                
## [145] "2019-10-26-command-line-crash-course.Rmd"                       
## [146] "2019-10-26-command-line-crash-course_files"                     
## [147] "2020-01-17-nse2r-intro.Rmd"                                     
## [148] "2020-04-17-handling-date-and-time-in-r.Rmd"                     
## [149] "2020-04-17-handling-date-and-time-in-r_files"                   
## [150] "airline.dta"                                                    
## [151] "airline.sas7bdat"                                               
## [152] "analysis.R"                                                     
## [153] "cline"                                                          
## [154] "config.yml"                                                     
## [155] "employee.sav"                                                   
## [156] "examples"                                                       
## [157] "hsb2.csv"                                                       
## [158] "hsb3.csv"                                                       
## [159] "hsb4.csv"                                                       
## [160] "imports_blorr.txt"                                              
## [161] "imports_olsrr.txt"                                              
## [162] "mydatabase.db"                                                  
## [163] "mypackage"                                                      
## [164] "myproject"                                                      
## [165] "online-retail.xlsx"                                             
## [166] "options.R"                                                      
## [167] "package_names.csv"                                              
## [168] "release.txt"                                                    
## [169] "sample.xls"                                                     
## [170] "transaction_data.csv"                                           
## [171] "zip_example.zip"

Great! Now, how do we specify the options? The additional options of a command must be stored as a character vector and specified using the args argument. In the below example, we delete the examples folder we created earlier while decompressing the zip_example.zip file.

system2(command = "rm",
        args    = c("-r", "examples"))
## character(0)

In some cases, we might want to redirect the output. Let us say we are writing message to a file using the echo command. In this cases, we want the output to be redirected to the release.txt file. The stdout argument can be used to redirect output to a file or the R console. In the below example, we redirect the output to a file.

system2(command = "echo", 
        args    = c("Great Truth"), 
        stdout  = "release.txt")

In the next example, we redirect the output to the R console by setting the value of the stdout argument to TRUE. If you are curious, set the value to FALSE and see what happens.

system2(command = "diff", 
        args    = c("imports_olsrr.txt", "imports_blorr.txt"),  
        stdout  = TRUE)
## Warning in system2(command = "diff", args = c("imports_olsrr.txt",
## "imports_blorr.txt"), : running command '"diff" imports_olsrr.txt
## imports_blorr.txt' had status 1
##  [1] "1,4c1,5"      "< car "       "< checkmate"  "< cli"        "< clisymbols"
##  [6] "---"          "> car"        "> caret"      "> checkmate"  "> clisymbols"
## [11] "> cli"       
## attr(,"status")
## [1] 1

The run() command from the processx package can be used to execute shell commands as well.

Execute Shell Commands in RStudio

In RStudio, commands can be executed from shell scripts by pressing Ctrl + Enter. Instead of sending the command to the R console, it is redirected to the terminal where it is executed as shown below.

RMarkdown

RMarkdown supports bash, sh and awk. This post was initially created using sh as the underlying operating system is Windows. Later, we used bash after installing the Windows subsystem for Linux. Click here to learn more.

R in the Shell

In this section, we will learn to execute R commands and scripts in the command line using:

  • R -e
  • Rscript -e
  • R CMD BATCH

The -e option allows us to specify R expression(s). R -e will launch R and then execute the code specified within quotes. Use semi-colon to execute multiple expressions as shown below. You will be able to run the below commands only if you are able to launch R from the command line. Windows users need to ensure that R is added to the path environment.

R -e "head(mtcars); tail(mtcars)"
## 
## R version 4.0.0 (2020-04-24) -- "Arbor Day"
## Copyright (C) 2020 The R Foundation for Statistical Computing
## Platform: x86_64-w64-mingw32/x64 (64-bit)
## 
## R is free software and comes with ABSOLUTELY NO WARRANTY.
## You are welcome to redistribute it under certain conditions.
## Type 'license()' or 'licence()' for distribution details.
## 
##   Natural language support but running in an English locale
## 
## R is a collaborative project with many contributors.
## Type 'contributors()' for more information and
## 'citation()' on how to cite R or R packages in publications.
## 
## Type 'demo()' for some demos, 'help()' for on-line help, or
## 'help.start()' for an HTML browser interface to help.
## Type 'q()' to quit R.
## 
## > head(mtcars); tail(mtcars)
##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1
##                 mpg cyl  disp  hp drat    wt qsec vs am gear carb
## Porsche 914-2  26.0   4 120.3  91 4.43 2.140 16.7  0  1    5    2
## Lotus Europa   30.4   4  95.1 113 3.77 1.513 16.9  1  1    5    2
## Ford Pantera L 15.8   8 351.0 264 4.22 3.170 14.5  0  1    5    4
## Ferrari Dino   19.7   6 145.0 175 3.62 2.770 15.5  0  1    5    6
## Maserati Bora  15.0   8 301.0 335 3.54 3.570 14.6  0  1    5    8
## Volvo 142E     21.4   4 121.0 109 4.11 2.780 18.6  1  1    4    2
## > 
## >

Rscript -e will run code without launching R.

Rscript -e "head(mtcars)"
##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

We can use Rscript to execute a R script as well. In the below example, we execute the code in analysis.R file.

Rscript analysis.R
##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

If you are more interested, try the littler package as well.

What we have not covered…

  • shell scripting
  • editing files
  • file permissions
  • user information
  • pipes
  • awk
  • sed

Summary

  • Shell is a text based application for viewing, handling and manipulating files
  • It is also known by the following names
    • CLI (Command Line Inteface)
    • Terminal
    • Bash (Bourne Again Shell)
  • Use system2() and processx::run() in R to execute shell commands
  • Use Rscript -e or R -e to execute R scripts from the command line
  • RStudio includes a Terminal (from version 1.1.383)
  • Execute commands from shell script in RStudio using Ctrl + Enter
  • RMarkdown supports bash, sh and awk

Feedback

If you see mistakes or want to suggest changes, please create an issue on the source repository or reach out to us at .