Set a parent shell's variable from a subshell

bash shell subshell
Matt Joiner picture Matt Joiner · Mar 21, 2013 · Viewed 66.6k times · Source

How do I set a variable in the parent shell, from a subshell?

a=3
(a=4)
echo $a

Answer

cdarke picture cdarke · Mar 21, 2013

The whole point of a subshell is that it doesn't affect the calling session. In bash a subshell is a child process, other shells differ but even then a variable setting in a subshell does not affect the caller. By definition.

Do you need a subshell? If you just need a group then use braces:

a=3
{ a=4;}
echo $a

gives 4 (be careful of the spaces in that one). Alternatively, write the variable value to stdout and capture it in the caller:

a=3
a=$(a=4;echo $a)
echo $a

avoid using back-ticks ``, they are deprecated and can be difficult to read.

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