how to handle bash * matching when there are no matches?

Question

The following bash snippet works great when there are actually *.txt files in the directory.

for txt in *.txt
do                                               
  echo "loading data from $txt"
done

When there aren't, the literal *.txt falls into the loop as $txt (not good).

How do I change this code so that when there are no *.txt files, the do ... done block is skipped?

@ott: `[ "*.txt" != '*.txt' ]` is always false -- both strings are in quotes, so neither gets checked for matches. If you remove the quotes from one it ... has other problems. — Gordon Davisson, Dec 14 '12 at 19:47
@GordonDavisson +1 for pointing this out: shell scripting seems to be full of surprises... — kfmfe04, Dec 14 '12 at 20:05
@GordonDavisson Indeed, it must be done in 2 steps to work: `files=$(echo *.txt)` and then: `if [ "${files}" != '*.txt' ] ; then`. — ott--, Dec 15 '12 at 14:17
@ott: That'd work (except for the odd case when there's a single file, actually named "*.txt"). — Gordon Davisson, Dec 15 '12 at 14:57
BTW, can be done as single line: `if [ "$(echo *.txt)" != '*.txt') ] ; then` — John Hascall, Aug 20 '18 at 19:57

score 17 · Answer 1 · edited Jun 25 '20 at 20:13

17

Put this magic incantation before the for statement:

shopt -s nullglob

(documentation)

edited Jun 25 '20 at 20:13

Cristian Ciupitu

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answered Dec 14 '12 at 14:02

kfmfe04

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2

Be aware that this may cause surprise side effects on commands like "ls *.txt" – noonex Feb 05 '19 at 14:47

score 6 · Answer 2 · answered Dec 14 '12 at 19:51

6

The nullglob option (@kfmfe04's answer) is best if you are using bash (not a brand-X shell), and don't have to worry about nullglob changing/breaking anything else. Otherwise, you can use this (slightly messier) option:

for txt in *.txt
do
  [ -e "$txt" ] || continue
  echo "loading data from $txt"
done

This silently skips files that don't exist (mainly "*.txt" if there were no matches, but possibly also files that were deleted between when the for generated the list and when the loop got to them...)

answered Dec 14 '12 at 19:51

Gordon Davisson

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A file might be deleted between `-e` invocation and later processing still... – Koterpillar Sep 25 '18 at 02:01
@Koterpillar True, but testing `-e` reduces the time window where deletion is a problem. – Gordon Davisson Sep 25 '18 at 02:31

how to handle bash * matching when there are no matches?

2 Answers2