Bash – How to Avoid For Loop Glob Mishaps?

bashwildcards

I am trying to set up a script that will loop over a set of directories, and do one thing when it finds .jpg files, and another when it finds .nef files. The problem is, if a directory does not have .jpg files for example (or .nef) then the glob entry is no longer an expanded glob, but just a string. For example:

my_dir="pictures/"
ext="JPG"
for f in "$my_dir"*."$ext"; do
    echo $f
done

if the my_dir folder has .JPG files in it, then they will be echoed correctly on the command line.

pictures/one.JPG
pictures/two.JPG

However, if my_dir has no .JPG files, then the loop will enter for one iteration and echo:

pictures/*.JPG

how do I construct this so that if the glob has no matches, it does not enter the for loop?

Best Answer

This is normal and default behavior: If globbing fails to match any files/directories, the original globbing character will be preserved.

If you want to get back an empty result instead, you can set the nullglob option in your script as follows:

$ shopt -s nullglob
$ for f in "$my_dir"*."$ext"; do echo $f; done
$

You can disable it afterwards with:

$ shopt -u nullglob

Related Solutions

Bash – How to programmatically tell if a filename matches a shell glob pattern

I don't believe that {bar,baz} is a shell glob pattern (though certainly /foo/ba[rz] is) but if you want to know if $string matches $pattern you can do:

case "$string" in 
($pattern) put your successful execution statement here;;
(*)        this is where your failure case should be   ;;
esac

You can do as many as you like:

case "$string" in
($pattern1) do something;;
($pattern2) do differently;;
(*)         still no match;;
esac

Bash – How to use ‘*’ to capture everything with exceptions

You can do this using the following extglob pattern in bash:

!(*t|*s|*a)_1.txt

Enable extglob at first (if not enabled) by:

shopt -s extglob

Then you can do:

for f in ~/admin/packages/!(*t|*s|*a)_1.txt; do ##Something; done

Example:

$ echo *_1.txt
A_1.txt Ab_1.txt A_t_1.txt A_ts_1.txt A_tsa_1.txt

$ shopt -s extglob

$ echo !(*t|*s|*a)_1.txt
A_1.txt Ab_1.txt

Shortened (thanks to chaos):

!(*[tsa])_1.txt

Best Answer

Related Solutions

Bash – How to programmatically tell if a filename matches a shell glob pattern

Bash – How to use ‘*’ to capture everything with exceptions

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