Find and replace value of an environment variable in source file

Question

I have a file which has environment variable listed like

 VAR_NAME=abc

and this file is sourced when needed. I want to add a new environment variable to the file if it's not present already. How do I search this file and replace/add a new value to it?

I was doing this till now:

echo "string_created" >> fileName

this just appends a line and after few runs there were multiple lines with diff values. I can remove this file after one run of my program but that isn't definitive.

If there's already a value set, do you want to remove it and replace it with the new value? — lurker
– lurker, Commented Jan 27, 2014 at 16:11

anubhava · Accepted Answer · 2014-01-27 15:26:14Z

1

You can use grep:

grep -q '^VAR_NAME=' file || echo 'VAR_NAME=abc' >> file

echo will execute when grep returns non-success return code.

answered Jan 27, 2014 at 15:26

anubhava

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3 Comments

tripleee Over a year ago

There is a race condition if multiple instances of this script could be running simultaneously. This is hard to fix with just shell script.

anubhava Over a year ago

Oh of course most of the shell scripts are not written with that requirement in place. However if there is any chance like that then creating a temporary .pid file might help.

that other guy Over a year ago

Fixing race conditions in scripts is trivial with flock.

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