Is there an easy way to set nullglob for one glob

bash glob shopt
derobert picture derobert · Feb 3, 2012 · Viewed 8.2k times · Source

In bash, if you do this:

mkdir /tmp/empty
array=(/tmp/empty/*)

you find that array now has one element, "/tmp/empty/*", not zero as you'd like. Thankfully, this can be avoided by turning on the nullglob shell option using shopt -s nullglob

But nullglob is global, and when editing an existing shell script, may break things (e.g., did someone check the exit code of ls foo* to check if there are files named starting with "foo"?). So, ideally, I'd like to turn it on only for a small scope—ideally, one filename expansion. You can turn it off again using shopt -u nullglob But of course only if it was disabled before:

old_nullglob=$(shopt -p | grep 'nullglob$')
shopt -s nullglob
array=(/tmp/empty/*)
eval "$old_nullglob"
unset -v old_nullglob

makes me think there must be a better way. The obvious "put it in a subshell" doesn't work as of course the variable assignment dies with the subshell. Other than waiting for the Austin group to import ksh93 syntax, is there?

Answer

estani picture estani · Feb 3, 2012

Unset it when done:

shopt -u nullglob

And properly (i.e. storing the previous state):

shopt -u | grep -q nullglob && changed=true && shopt -s nullglob
... do whatever you want ...
[ $changed ] && shopt -u nullglob; unset changed

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