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author | jilles <jilles@FreeBSD.org> | 2010-12-28 21:27:08 +0000 |
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committer | jilles <jilles@FreeBSD.org> | 2010-12-28 21:27:08 +0000 |
commit | 74d9b02bb00830c58e7572986e81ef97d2948ed6 (patch) | |
tree | 938df618f5e6962d48e61103d210b5c6d2101fa1 /etc/libalias.conf | |
parent | d20b96d0f2ef605d9476d5c27ffe395c0e237253 (diff) | |
download | FreeBSD-src-74d9b02bb00830c58e7572986e81ef97d2948ed6.zip FreeBSD-src-74d9b02bb00830c58e7572986e81ef97d2948ed6.tar.gz |
sh: Don't do optimized command substitution if expansions have side effects.
Before considering to execute a command substitution in the same process,
check if any of the expansions may have a side effect; if so, execute it in
a new process just like happens if it is not a single simple command.
Although the check happens at run time, it is a static check that does not
depend on current state. It is triggered by:
- expanding $! (which may cause the job to be remembered)
- ${var=value} default value assignment
- assignment operators in arithmetic
- parameter substitutions in arithmetic except ${#param}, $$, $# and $?
- command substitutions in arithmetic
This means that $((v+1)) does not prevent optimized command substitution,
whereas $(($v+1)) does, because $v might expand to something containing
assignment operators.
Scripts should not depend on these exact details for correctness. It is also
imaginable to have the shell fork if and when a side effect is encountered
or to create a new temporary namespace for variables.
Due to the $! change, the construct $(jobs $!) no longer works. The value of
$! should be stored in a variable outside command substitution first.
Diffstat (limited to 'etc/libalias.conf')
0 files changed, 0 insertions, 0 deletions