mjhjmtu

My question is the zsh equivalent of the question asked here: How can I use a variable as a case condition? I would like to use a variable for the condition of a case statement in zsh. For example:

input="foo"
pattern="(foo|bar)"

case $input in
$pattern)
 echo "you sent foo or bar"
;;
*)
 echo "foo or bar was not sent"
;;
esac

I would like to use the strings foo or bar and have the above code execute the pattern case condition.

With this code saved to the file first,

pattern=fo*
input=foo
case $input in
$pattern)
 print T
 ;;
fo*)
 print NIL
 ;;
esac

under -x we may observe that the variable appears as a quoted value while the raw expression does not:

% zsh -x first
+first:1> pattern='fo*'
+first:2> input=foo
+first:3> case foo (fo*)
+first:3> case foo (fo*)
+first:8> print NIL
NIL

That is, the variable is being treated as a literal string. If one spends enough time in zshexpn(1) one might be aware of the glob substitution flag

 $~spec
 Turn on the GLOB_SUBST option for the evaluation of spec; if the
 `~' is doubled, turn it off. When this option is set, the
 string resulting from the expansion will be interpreted as a
 pattern anywhere that is possible,

so if we modify $pattern to use that

pattern=fo*
input=foo
case $input in
$~pattern) # !
 print T
 ;;
fo*)
 print NIL
 ;;
esac

we see instead

% zsh -x second
+second:1> pattern='fo*'
+second:2> input=foo
+second:3> case foo (fo*)
+second:5> print T
T

for your case the pattern must be quoted:

pattern='(foo|bar)'
input=foo
case $input in
$~pattern)
 print T
 ;;
*)
 print NIL
 ;;
esac