I have set the shell variable. I no longer need the variable. How do I undefine or unset a variable in bash on a Linux or Unix-like desktop system?
Creating and setting variables within a script (or shell prompt) is fairly simple. The syntax is:
export vech= Bus
How do I unset variables in bash?
Use unset command to delete the variables during program execution. It can remove both functions and shell variables. The syntax is:
To unset the $vech, enter:
A note about readonly variables
Please note that some variables cannot be unset if they are defined as readonly by the system or sysadmin:
-bash: unset: BACKUPDIR: cannot unset: readonly variable
You can define your readonly variables using the following syntax:
declare -r BACKUPDIR= foo
How do I unset a shell function on bash?
The syntax is as follows to treat each varName as a shell function:
unset -f varName
unset -f tarhelper
For more info, type:
To add a variable which will be available for remote login sessions (i.e. when you ssh to the user from remote system), modify
$ vi .bash_profile
Add the following line to
.bash_profile file at the bottom.
export VAR2='This is TecMint Home'
When on sourcing this file, the variable will be available when you ssh to this user, but not on opening any new local terminal.
$ source .bash_profile $ echo $VAR2
VAR2 is not initially available but, on doing ssh to user on localhost, the variable becomes available.
$ ssh tecmint@localhost $ echo $VAR2
To remove this variable, remove the line from
/etc/profile file and re-source it.
c.) However, if you want to add any environment which you want to be available all throughout the system, on both remote login sessions as well as local sessions( i.e. opening a new terminal window) for all users, just export the variable in /etc/environment file.
export VAR12='I am available everywhere'
After that just source the file and the changes would take effect.
$ source /etc/environment $ echo $VAR12 $ sudo su $ echo $VAR12 $ exit $ ssh localhost $ echo $VAR12
Here, as we see the environment variable is available for normal user, root user, as well as on remote login session (here, to localhost).
To clear out this variable, just remove the entry in the /etc/environment file and re-source it or login again.
NOTE: Changes take effect when you source the file. But, if not then you might need to log out and log in again.
Thus, these are few ways we can modify the environment variables. If you find any new and interesting tricks for the same do mention in your comments.