Setting environment variables in Linux using Bash

Question

In tcsh, I have the following script working:

#!/bin/tcsh
setenv X_ROOT /some/specified/path

setenv XDB    ${X_ROOT}/db
setenv PATH   ${X_ROOT}/bin:${PATH}

xrun -d xdb1 -i $1 > $2

What is the equivalent to the tcsh setenv function in Bash?

Is there a direct analog? The environment variables are for locating the executable.

Answer 1

I think you're looking for export - though I could be wrong.. I've never played with tcsh before. Use the following syntax:

export VARIABLE=value

Answer 2

The reason people often suggest writing

VAR=value
export VAR

instead of the shorter

export VAR=value

is that the longer form works in more different shells than the short form. If you know you're dealing with bash, either works fine, of course.

Answer 3

Set a local and environment variable using Bash on Linux

Check for a local or environment variables for a variable called LOL in Bash:

el@server /home/el $ set | grep LOL
el@server /home/el $
el@server /home/el $ env | grep LOL
el@server /home/el $

Sanity check, no local or environment variable called LOL.

Set a local variable called LOL in local, but not environment. So set it:

el@server /home/el $ LOL="so wow much code"
el@server /home/el $ set | grep LOL
LOL='so wow much code'
el@server /home/el $ env | grep LOL
el@server /home/el $

Variable 'LOL' exists in local variables, but not environment variables. LOL will disappear if you restart the terminal, logout/login or run exec bash.

Set a local variable, and then clear out all local variables in Bash

el@server /home/el $ LOL="so wow much code"
el@server /home/el $ set | grep LOL
LOL='so wow much code'
el@server /home/el $ exec bash
el@server /home/el $ set | grep LOL
el@server /home/el $

You could also just unset the one variable:

el@server /home/el $ LOL="so wow much code"
el@server /home/el $ set | grep LOL
LOL='so wow much code'
el@server /home/el $ unset LOL
el@server /home/el $ set | grep LOL
el@server /home/el $

Local variable LOL is gone.

Promote a local variable to an environment variable:

el@server /home/el $ DOGE="such variable"
el@server /home/el $ export DOGE
el@server /home/el $ set | grep DOGE
DOGE='such variable'
el@server /home/el $ env | grep DOGE
DOGE=such variable

Note that exporting makes it show up as both a local variable and an environment variable.

Exported variable DOGE above survives a Bash reset:

el@server /home/el $ exec bash
el@server /home/el $ env | grep DOGE
DOGE=such variable
el@server /home/el $ set | grep DOGE
DOGE='such variable'

Unset all environment variables:

You have to pull out a can of Chuck Norris to reset all environment variables without a logout/login:

el@server /home/el $ export CAN="chuck norris"
el@server /home/el $ env | grep CAN
CAN=chuck norris
el@server /home/el $ set | grep CAN
CAN='chuck norris'
el@server /home/el $ env -i bash
el@server /home/el $ set | grep CAN
el@server /home/el $ env | grep CAN

You created an environment variable, and then reset the terminal to get rid of them.

Or you could set and unset an environment variable manually like this:

el@server /home/el $ export FOO="bar"
el@server /home/el $ env | grep FOO
FOO=bar
el@server /home/el $ unset FOO
el@server /home/el $ env | grep FOO
el@server /home/el $

Answer 4

VAR=value sets VAR to value.

After that export VAR will give it to child processes too.

export VAR=value is a shorthand doing both.

Answer 5

export VAR=value will set VAR to value. Enclose it in single quotes if you want spaces, like export VAR='my val'. If you want the variable to be interpolated, use double quotes, like export VAR="$MY_OTHER_VAR".