For example,
a="1|2|3"
b=3
case $b in
$a )
echo in
;;
* )
echo out
;;
*)
esac
I'd like $a to be expanded as 1|2|3. But seems it cannot work as expected. Thanks for any suggestion.
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ElpieKay
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1take a look at this; http://stackoverflow.com/questions/4687722/dynamic-case-statement-in-bash – Mustafa DOGRU Dec 22 '16 at 13:19
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1Solvable via extglob: http://stackoverflow.com/a/13254908/1030675 – choroba Dec 22 '16 at 13:55
1 Answers
2
The problem is that | is not part of the pattern, but part of the case statement's syntax that separates two patterns. The following would work:
foo=3
b1=1
b2=2
b3=3
case $foo in
$b1|$b2|$b3) echo match ;;
esac
The | needs to be visible to the parser before parameter expansion occurs to act as a pattern separator. If the | is produced by a parameter expansion, it is treated as a literal character to match as part of a pattern.
chepner
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1A `case $b in +($a) ) echo in ;; ` also works correctly provided that a `shopt -s extglob` is in effect. – Dec 22 '16 at 19:34
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Yeah, I considered adding a note about that when I saw @choroba's comment, but then decided to just explain why placing a bar in a parameter alone didn't work. – chepner Dec 22 '16 at 19:38