Why I can't set environment value in my BASH script?

skiron.liu · 06-20-2010, 02:46 AM

for example

Code:

#!/bin/bash
  PATH=$PATH:/opt/bin
  export PATH

I run "echo $PATH" after this script. The "/opt/bin" don't append to "PATH".

colucix · 06-20-2010, 03:01 AM

The reason is that every script/process has its own environment (scope) and using the export statement it can transfer variables or functions to its child processes, but not backward to the parent shell. You can achieve this task by "sourcing" the script, not by "executing" it. In bash this means:

Code:

. test.sh

where the dot is the source command. In this way all the statements inside the script are simply executed in the current shell and all the variable assignments are in effect.

This is the reason why environment variables are defined in configuration files like /etc/bashrc, /etc/profile or $HOME/.bashrc and $HOME/.bash_profile. These and/or other files are sourced (not executed) every time you start a new shell session. Hope this helps.

druuna · 06-20-2010, 03:01 AM

Hi,

If you execute a script, the variables set are only valid/accessible in that, newly created, shell and it's sub-shells and not in the shell you executed the script in (mother - child principle).

If you want those variables to be accessible in your current shell you need to parse the script, not execute it:
source <scriptname> or . <scriptname>

Hope this helps.

skiron.liu · 06-20-2010, 03:25 AM

Thank you~

Code:

PATH=/sbin:/usr/sbin:/bin:/usr/bin:$basedir/bin
export PATH

That two statement in "MySQL" daemon start/stop script. When MySQL started but "$basedir/bin" not append to PATH. The reason is same too?

druuna · 06-20-2010, 03:41 AM

Hi,

In short: Yes.

You need to add the full path. I.e.:

PATH=/sbin:/usr/sbin:/bin:/usr/bin:/my/own/bin.

Hope this helps.

EDIT
Also: don't use $PATH in these startup scripts (as in PATH=$PATH:../../..), this variable isn't present/set when your box boots.
/EDIT