Is it possible to test whether a bash script was executed with -x?
I'm writing a script which also runs some remote scripts, and I'd like to be able to do something like:
USE_X="$( run_with_x && "-x" || "" )"
ssh $host "bash $USE_X some_script.sh"
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5 Answers
Just look at the $- variable.
USE_X=`case "$-" in *x*) echo "-x" ;; esac`
(Yup, I did manage to do that without invoking grep. Save the pids!)
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1
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2What a waste of pid!
case $- in *x*) USE_X="-x";; *) USE_X=;; esac@bbaja42 It doesn't expand to anything: it's a pattern that the string$-is matched against.Gilles 'SO- stop being evil'– Gilles 'SO- stop being evil'2011-10-03 21:08:36 +00:00Commented Oct 3, 2011 at 21:08 -
@Gilles Your example also contains unnecessary part:
*) USE_X=;;changes nothing, ifUSE_Xwas not set previously. Also, the wholecaseconstruct is unnecessary (see my version - isn't that simpler?)rozcietrzewiacz– rozcietrzewiacz2011-10-04 16:12:33 +00:00Commented Oct 4, 2011 at 16:12 -
@rozcietrzewiacz This part is unnecessary if
USE_Xhas been initialized earlier on. I don't consider your version simpler: it's a few characters shorter (and even then only ifUSE_Xhas been initialized, otherwise it's longer), but at the expense of clarity and portability.Gilles 'SO- stop being evil'– Gilles 'SO- stop being evil'2011-10-04 17:11:45 +00:00Commented Oct 4, 2011 at 17:11 -
@Gilles Portability is not the subject of this question, it is about bash. Initializing
USE_Xis not necessary for the purpose of OP's intended use (to pass$USE_Xto further scripts). Usingcaseconstruct looks less clear and natural than a regular condition evaluation in my view.rozcietrzewiacz– rozcietrzewiacz2011-10-04 17:53:58 +00:00Commented Oct 4, 2011 at 17:53
This expression will be true if the script is run with -x, false otherwise: [[ $- =~ x ]]
So this expression will be "-x" if the script is run with -x and "" (empty) otherwise: $([[ $- =~ x ]] && echo "-x")
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It's a stretch to say "readable" and "bash" in the same sentence, but since any non-casual bash user MUST get familiar with the bash regex syntax, your (currently lowest-voted) answer wins for readability in my book (and, of course, doesn't require starting any processes or anything astoundingly inefficient).Ron Burk– Ron Burk2017-04-24 21:39:09 +00:00Commented Apr 24, 2017 at 21:39
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1This is the best answer!Chris Cogdon– Chris Cogdon2017-06-28 15:54:25 +00:00Commented Jun 28, 2017 at 15:54
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This expression removes all non-x characters from $-, so it is empty if there is no x:
${-//[^x]}If you assign this to variable, like:x=${-//[^x]}then the following expression will be empty when there was no x and -x otherwise:${x:+-x}Combine like:x=${-//[^x]} USE_X=${x:+-x}Or if you don't want to use an extra variable, you can reuse USE_X:USE_X=${-//[^x]} USE_X=${USE_X:+-x}This is much much faster than doing a regular expression comparison! (But less readable just looking at the code, figuring out what it does...)PePa– PePa2018-05-22 08:47:32 +00:00Commented May 22, 2018 at 8:47
Probably the simplest way of parsing $-, similar to dagbrown's method (also pure bash), but without using case and backticks (subshell):
if [[ ${-/x} != $- ]] ; then USE_X="-x"; fi
or even shorter:
[[ ${-/x} != $- ]] && USE_X="-x"
Note that [[ is not an invocation of test builtin program (as is the case with [), but a bash syntax construct (according to man bash and this dev recommendation). So I claim it to be "purer bash" ;)
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Nice solution. I suggest tagging '|| USE_X="+x"' on the end of the second expression so you may then call 'set "$USE_X"' and it will work to restore the initial setting whether or not xtrace was set.Binary Phile– Binary Phile2014-12-23 15:14:15 +00:00Commented Dec 23, 2014 at 15:14
After reading man pages and grepping for things, here's the solution:
$ cat show_x.sh
#!/bin/bash
if [ "$(set | grep xtrace)" ]; then
echo "xtrace is on. :D"
else
echo "xtrace is off. :("
fi
Result:
$ bash show_x.sh
xtrace is off. :(
$ bash -x show_x.sh
++ set
++ grep xtrace
+ '[' SHELLOPTS=braceexpand:hashall:interactive-comments:xtrace ']'
+ echo 'xtrace is on. :D'
xtrace is on. :D
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"set" will show you all the functions and env vars to, and if any of those contain "xtrace" the solution will fail.Chris Cogdon– Chris Cogdon2017-06-28 15:40:53 +00:00Commented Jun 28, 2017 at 15:40
The bash man page documents set -o xtrace as equivalent to set -x, which in turn is equivalent to giving -x as an argument to the shell. (So far, this is compatible with SUSv3 sh, with the caveat that -o option is required "if the system supports the User Portability Utilities option".)
Also, set -o without an option prints the current status of all of the -o options. (SUSv3 specifies this as well, but not usefully; the format is unspecified, so you can only depend on it if you know you're running a shell that uses a format similar to bash's.)
So, the pipeline set -o | grep xtrace | grep -q on should be what you're looking for.
