Created: 2019-02-15 — modified: 2019-02-18 — tags: Bash
set -e might work not as you expected inside (parentheses).
You know what
set -e does, right? It aborts execution as soon as one of commands returns non-0 result. For example, the following code:
set -e true 1 false 2 true 3
will be executed like this:
$ bash -x test.sh + set -e + true 1 + false 2
Note that here I'm using the
true debugging trick mentioned in previous blog post.
Above is true for parenthesised blocks, too:
set -e ( true 1 false 2 true 3 ) true 4
Output of running this script will be exactly the same as before.
But what if you want to continue after failing block? For example, writing this:
set -e ( true 1 false 2 true 3 ) || true 4 true 5
One might expect parenthesised block to be aborted after
false 2 command, then "alternative" command
true 4 to be executed, and execution continue. But actual execution is like this:
$ bash -x test.sh + set -e + true 1 + false 2 + true 3 + true 5
Before you ask - it will be the same even if you add extra
set -e inside the block, too.
What happens is that, it seems,
set -e is totally ignored inside the block, happily continuing to
true 3 statement,
and its return code is used as return code of the whole braced statement - hence
true 4 command is not executed.
Same happens with parentheses inside
$ cat test.sh set -e if ( true 1 false 2 true 3 ); then true pass else true fail fi $ bash -x test.sh + set -e + true 1 + false 2 + true 3 + true pass
First workaround is putting
&& at the end of each line, like this:
$ cat test.sh set -e ( true 1 && false 2 && true 3 ) || true 4 true 5 $ bash -x test.sh + set -e + true 1 + false 2 + true 4 + true 5
But well, in that case you can omit parentheses altogether:
set -e true 1 && false 2 && true 3 || true 4 true 5
Not sure what indentation should look like, though.
Another workaround is making it
set +e on the outside,
set -e on the inside, and preserving return code, like this:
$ cat test.sh set -e set +e ( set -e true 1 false 2 true 3 ) result=$? set -e test "$result" = "0" || true 4 true 5 $ bash -x test.sh + set -e + set +e + set -e + true 1 + false 2 + result=1 + set -e + test 1 = 0 + true 4 + true 5