Linux command List

 Let's see the list of Linux commands which are commonly used. This list is helpful for beginners and professionals both.

Commands	Description
alias	Converts complex commands into simpler ones.
bzip2 / bunzip2	Compresses a file / Decompress a bzip2 file.
bzcat / bzmore	Displays files compressed with bzip2.
cal	Displays calendar.
cat	It is a multi-function command.
cd	Changes the current working directory.
chage	Sets an expiration date for a user account.
chgrp	Changes group.
chmod	Changes permission for a file or directory.
chown	Changes the owner of a file or directory.
chsh	Changes the shell.
clear	Clears the terminal.
comm	Compares two streams or files.
cp	Copies file content from one file to another file.
cut	Used to display the desired column from a file.
date	Displays the current date.
df	Checks the disk space in the system.
echo	Prints the typed word on the terminal.
exit	Exits from the current user group to the last group.
export	Exports shell variables to other shells.
file	Displays the type of file.
find	Finds files for a particular search.
gpasswd	Transfers group membership to another user.
grep	Filters lines of text containing a certain string.
groupadd	Creates a group.
groupdel	Permanently removes a group.
groupmod	Changes group name.
groups	Displays the group name to which the current user belongs to.
gzip / gunzip	Compresses a file / Decompress a gzip file.
head	Displays the first ten lines of a file.
history	Displays older commands from the shell command history.
HISTSIZE	Determines the number of commands to be stored in the current environment.
HISTFILE	Displays the file that contains the history.
HISTFILESIZE	Sets the number of commands kept in the history file.
id	Tells about the user's id in the system.
less	Displays file content according to the width of the terminal.
locate	Searches a file in the database.
ls	Lists all the files of a directory.
man	Displays the manual page for the specified command.
mkdir	Creates directory.
more	Displays one output screen at a time.
mv	Renames directories or files.
od	Displays a file content in octal format.
passwd	Set a password for a user group.
pwd	Display the current working directory location.
PS1	Change the prompt name in the terminal.
rename	Renames more than one file at once.
rm	Removes a file.
rmdir	Removes a directory.
set -o noclobber	Prevents file from getting overwritten.
set +o noclobber	Allows overwriting in the existing file.
set -u	Displays undefined variables as an error.
set +u	Displays nothing for an undefined variable.
set -x	Displays shell expansion.
set +x	Disables shell expansion.
sed	Performs editing in streams.
sleep	Waits for the specified number of seconds.
sort	sorts the content in alphabetical order.
su	It allows a user to run a shell as another user.
sudo	It allows a user to start a program with the credentials of another user.
tac	Displays file content in the opposite order.
tail	Displays the last ten lines of a file.
tar	Compresses a directory.
tee	Puts stdin on stdout and then into a file.
time	Displays time taken to execute a command.
touch	It creates an empty file.
tr	Translates characters.
type	Displays information about command type.
uniq	Sorts and display multi times repeating lines only once.
unset	Removes a variable from a shell.
useradd	Adds users.
userdel	Deletes users.
usermod	Modifies the properties of a user.
vi	Opens vi editor to write a program.
w	Displays who is logged on and what are they doing.
wc	Counts words, lines, and characters.
who	Tells who is logged on the system.
whoami	Tells the name of the user.
who am i	Displays the line pointing to your current session.
zcat / zmore	Views the files compressed with gzip.

Linux export Command

 The export command is a built-in utility of Linux Bash shell. It is used to ensure the environment variables and functions to be passed to child processes. It does not affect the existing environment variable.

Environment variables are set when we open a new shell session. At any time, if we change any variable value, the shell has no way to select that change. The export command allows us to update the current session about the changes that have been made to the exported variable. We do not need to wait to start a new shell session.

Syntax:

1. export [-f] [-n] [name[=value] ...] or export -p  

Let's have a look at various examples of the export command:

Example1: The export command without any argument

The basic export command will display all the exported environment variables of your system. It is executed as follows:

1. export  

Consider the below snap of output:

Example2: Display all exported variable on current shell

To display all the exported environment variable of the current shell, execute the command with -p option as follows:

1. export -p  

Consider the below snap of output:

Example3: Using export with functions

To use a function with the export command, use the -f option. If we do not use this option, it will be considered as a variable, not function.

Syntax:

1. export -f function_name  

We are exporting a function 'name' as follows:

1. name() { echo "Javatpoint";}  

To export the above function, execute the command as follows:

1. export -f name  

Now, invoke the bash shell to execute the function:

1. bash  

To call the function, enter the function name:

1. name  

Consider the below output:

let's create another function 'hello,' execute the command as follows:

1. function hello  
2. > {  
3. > echo hello, welcome to javatpoint  
4. > }  

To export the above function, execute the command as follows:

1. export -f hello  

Consider the below output:

Example4: Assign a value before exporting a function or variable:

The export command allows us to assign a value before exporting a function. Consider the below command:

1. export name[=value]  

For example, assign a value to a variable as follows:

1. a=5  

now export it as:

1. export a  

we can verify the assignment by using the printenv command as follows:

1. printenv a  

Consider the below output:

Example5: Set vim as default editor:

The vim editor is the most widely used text editor for the Linux systems. We can set the vim as default text editor by using the export command.

To set the vim as a default text editor, execute the following command:

1. export EDITOR=/usr/bin/vim  
2. export | grep EDITOR  

The above commands will not show any confirmation. Consider the below output:

Example6: Set an environment variable

To create a new variable, use the export command followed by a variable name and its value.

Syntax:

1. export NAME=VALUE  

To create a new variable, 'sys,' execute the command as follows:

1. export  sys=50  

The echo command is used to display the variable:

1. echo sys  

To display the value of the variable, use the $ symbol before the variable name

1. echo $sys  

Consider the below output:

Linux Set Command

 Linux set command is used to set and unset certain flags or settings within the shell environment. These flags and settings determine the behavior of a defined script and help in executing the tasks without facing any issue. The values of shell attributes and parameters can be changed or displayed by using the set command.

Syntax:

1. set [options]  

To know about how to set the environment variable in Linux, visit Here.

Options: The supported options by the set command are as following:

• -a: It is used to mark variables that are modified or created for export.
• -b: It is used to notify of job termination immediately.
• -e: It is used to exit immediately if a command exits with a non-zero status.
• -f: It is used to disable the file name generation (globbing).
• -h: It is used to save the location of commands where they looked up.
• -k: It is used to place all assignment arguments in the environment variable of a command, except those that precede the command name.
• -m: It is used to enable Job control.
• -n: It is used to read commands.
• -o: It is used for option-name.
• -p: It is used to disable the processing of the '$ENV' file and import shell functions. It is turned on whenever the real and effective user ids do not match. Turning off this option may cause the working uid and gid to be set as the authorized uid and gid.
• -t: It is used to exit from the command after executing one command.
• -u: It is used to treat unset variables as an error when substituting.
• -v: It is used to print shell input lines.
• -x: It is used to print commands and their arguments in a sequential way (as they are executed).
• -B: It is used to perform brace expansion by the Shell.
• -C: It is used to disallow existing regular files to be overwritten by redirection of output.
• -E: It is used if the ERR trap is inherited by the shell functions.
• -H: It is used to enable style history substitution. By default, it is on when the shell is interactive.
• -P: It is used if we do not want to follow symbolic links when executing commands.
• -T: If this flag is set, the DEBUG trap is inherited by the shell functions.

Note: To turn off the above flags, use the '+' rather than '-' symbol.

To better understand the set command, let's see a brief introduction of the shell variable:

Shell Variable

A variable is a character string that can hold a value. The assigned value could be anything such as number, filename, text, or any other data type. It is just like a pointer to the actual data. The shell allows us to create, delete, and assign variables.

The variable name can have any letters, numbers, or underscore (_) character. We cannot have the characters such as "! *, or -", because these special characters have other meanings for the shell. According to Unix naming convention, the Unix shell variable must have their names in UPPERCASE.

Examples of the set command

Turn debugging information on or off.

The '-x' option is used with the set command to show command and their arguments. It is useful for debugging the shell script.

Execute the following command:

To turn on the debugging information:

1. set -x  

To turn off the debugging information:

1. set +x  

Disable Bash's default behavior.

To disable the default behavior of Bash, execute the command as follows:

1. set -C  

Stop a script immediately.

To stop a script immediately, execute the following command:

1. set -e  

Getting Help

If you get stuck during the use of the set command, you can access the help documentation from your terminal. To access the help manual, execute the below command:

1. set --help