bash check for empty string/line using -z

Question

I am relatively new to bash scripting, and I have the following script, which is not giving me results I expect. So, my script looks like so:

#!/bin/bash

echo "Today is $(date)"
shopt -s nullglob

FILES=/some/empty/dir/with/no/text/files/*.txt
#echo $FILES


if [ -z "$FILES" ]
then
    echo 'FILES variable is empty'
    exit
else
    echo 'FILES variable is not empty'
    echo 'done' > write_file_out.dat
fi

So, the directory I am trying to use FILES on is completely empty - and still, when I do if [ -z "$FILES" ] it seems to say that it is not empty.

Baffled by this - wondering if someone can point me in the right direction.

anubhava · Accepted Answer · 2014-08-19 18:04:55Z

5

Instead of:

FILES=/some/empty/dir/with/no/text/files/*.txt

You need to use:

FILES="$(echo /some/empty/dir/with/no/text/files/*.txt)"

Otherwise $FILES will be set to: /some/empty/dir/with/no/text/files/*.txt and this condition [ -z "$FILES" ] will always be false (not empty).

You can also use BASH arrays for shell expansion:

FILES=(/some/empty/dir/with/no/text/files/*.txt)

And check for:

[[ ${#FILES[@]} == 0 ]]

for empty check.

edited Aug 19, 2014 at 18:04

answered Aug 19, 2014 at 17:59

anubhava

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17 Comments

Etan Reisner Over a year ago

Or FILES=(/some/empty/dir/with/no/text/files/*.txt) and then test for an empty array since that is much better to work with when you actually need to do something with the files.

AJW Over a year ago

files will NOT be set to /some/empty/dir/with/no/text/files/*.txt because I am using shopt -s nullglob You can try using echo $FILES to see this

glenn jackman Over a year ago

@AJW, but you were quoting the variable: [ -z "$FILES" ] -- that prevents filename expansion. That's also the difference between echo $FILES and echo "$FILES". When you declare the variable, filename expansion does not happen, not until you use the variable.

AJW Over a year ago

thanks a tonne @anubhava - I used your bash arrays for shell expansion (thanks also to @EtanReisner) - and it works perfectly.

AJW Over a year ago

ok - got it - thanks again! Think I have solved it - obviously, with your help :)

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