CODEWITHSUNDEEP
shell
not-a-user
not-a-user

Reputation: 4327

Does the shell run commands before pipe in a subshell?

x=0; { x=1; echo $x; } | cat; echo $x

prints

1
0

while I expected

1
1.

Why? At last, curly brackets create no subshell.

I tested with bash and busybox sh (ash).

Upvotes: 0

Views: 74

Answers (1)

glenn jackman
glenn jackman

Reputation: 246744

In bash both sides of a pipeline are run in subshells (https://www.gnu.org/software/bash/manual/bashref.html#Pipelines) unless you shopt -s lastpipe; set +m, where the last command in a pipe is executed in the current shell

$ sum=0; seq 10 | while read n; do ((sum+=n)); done; echo $sum
0
$ shopt -s lastpipe
$ sum=0; seq 10 | while read n; do ((sum+=n)); done; echo $sum
0
$ set +m
$ sum=0; seq 10 | while read n; do ((sum+=n)); done; echo $sum
55

In your example, the first command in the pipeline will always be run in a subshell.

I can't speak for ash

Upvotes: 2

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