Replace value of an environment variable declared in a file

Question

There is a file env.sh, which defines environment variables:

$cat env.sh export var1=1 export var2=2

I want to replace the value of var1 inside of the file with 3, so that

$cat env.sh export var1=3 export var2=2

Is there way to do it without string/regexp matching magic?

I read a lot about envsubst, but still was not able to figure out how to apply it to the task.

I'm confused. Can you not just edit the file and replace the value? What distro are you using? You may also be able to edit a .bashrc or .bash_profile and simply overwrite the value of var1 — jasonmclose
– jasonmclose, Commented Aug 21, 2019 at 12:51
@jasonmclose I could. However this step should be a bash command. The value of var1 is generated as part of the process and as soon as it is generated it needs to be replaced in a file. — Denys
– Denys, Commented Aug 21, 2019 at 12:53
Not very elegant, append a new line: echo "export var1=3" >> env.sh — Cyrus
– Cyrus, Commented Aug 21, 2019 at 12:53
Thank you, that is an option. I want to have only one definition of var1 in the file though — Denys
– Denys, Commented Aug 21, 2019 at 12:55
This is just a file-editing task. Use an editor like ed, sed, or ex. — chepner
– chepner, Commented Aug 21, 2019 at 13:18

Cyrus · Accepted Answer · 2019-08-21 13:16:39Z

Without regex in a script:

#!/bin/bash source env.sh export var1=3 declare -p var1 > env.sh declare -p var2 >> env.sh

Output to env.sh:

declare -x var1="3" declare -x var2="2"

declare -x is synonymous with export.

chepner · Accepted Answer · 2019-08-21 13:24:13Z

Just use a scriptable editor like ed:

$ cat env.sh export var1=1 export var2=2 $ printf '/var1=/s/=.*/var1=3/\nw\n' | ed env.sh 28 28 $ cat env.sh export var1=3 export var2=2

2 Answers 2