When to wrap quotes around a shell variable?

linux bash shell unix quotes
Cristian picture Cristian · Apr 9, 2012 · Viewed 70.6k times · Source

Could someone tell me whether or not I should wrap quotes around variables in a shell script?

For example, is the following correct:

xdg-open $URL 
[ $? -eq 2 ]

or

xdg-open "$URL"
[ "$?" -eq "2" ]

And if so, why?

Answer

paxdiablo picture paxdiablo · Apr 9, 2012

General rule: quote it if it can either be empty or contain spaces (or any whitespace really) or special characters (wildcards). Not quoting strings with spaces often leads to the shell breaking apart a single argument into many.

$? doesn't need quotes since it's a numeric value. Whether $URL needs it depends on what you allow in there and whether you still want an argument if it's empty.

I tend to always quote strings just out of habit since it's safer that way.

Related questions

How to run a shell script on a Unix console or Mac terminal?

I know it, forget it and relearn it again. Time to write it down.

Read More
Given two directory trees, how can I find out which files differ by content?

If I want find the differences between two directory trees, I usually just execute: diff -r dir1/ dir2/ This outputs exactly what the differences are between corresponding files. I'm interested in just getting a list of corresponding files whose content …

Read More
Linux: copy and create destination dir if it does not exist

I want a command (or probably an option to cp) that creates the destination directory if it does not exist. Example: cp -? file /path/to/copy/file/to/is/very/deep/there

Read More