Denys Vlasenko eb60777769 ash: eval: Prevent recursive PS4 expansion ...

Date: Wed, 27 May 2020 13:19:10 +1000
eval: Prevent recursive PS4 expansion

    Yaroslav Halchenko <yoh@onerussian.com> wrote:
    > I like to (ab)use PS4 and set -x for tracing execution of scripts.
    > Reporting time and PID is very useful in this context.
    >
    > I am not 100% certain if bash's behavior (of actually running the command
    > embedded within PS4 string, probably eval'ing it) is actually POSIX
    > compliant, posh seems to not do that; but I think it is definitely not
    > desired for dash to just stall:
    >
    > - the script:
    > #!/bin/sh
    > set -x
    > export PS4='+ $(date +%T.%N) [$$] '
    > echo "lets go"
    > sleep 1
    > echo "done $var"
    >
    > - bash:
    > /tmp > bash --posix test.sh
    > +export 'PS4=+ $(date +%T.%N) [$$] '
    > +PS4='+ $(date +%T.%N) [$$] '
    > + 09:15:48.982296333 [2764323] echo 'lets go'
    > lets go
    > + 09:15:48.987829613 [2764323] sleep 1
    > + 09:15:49.994485037 [2764323] echo 'done '
    > done
    >
    ...
    > - dash: (stalls it set -x)
    > /tmp > dash test.sh
    > +export PS4=+ $(date +%T.%N) [$$]
    > ^C^C

    This patch fixes the infinite loop caused by repeated expansions
    of PS4.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2021-09-09 16:29:37 +02:00

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