Timeline for How to determine if a bash variable is empty?
Current License: CC BY-SA 4.0
15 events
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| Apr 15 at 9:19 | comment | added | metablaster |
Any valid reason for if [ -z "${VAR}" ]; instead of if [ -z "$VAR" ]; isn't first one for arrays?
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| Mar 31, 2022 at 7:38 | comment | added | Timo |
More info on -n as the inverse of -z from man test: -n string True if the length of string is nonzero.
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| May 24, 2020 at 12:49 | history | edited | 030 | CC BY-SA 4.0 |
added 2 characters in body
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| Nov 17, 2019 at 7:41 | comment | added | Sang |
In Bash, [[ -v VAR]] can be used to check if VAR is defined, [[ -z $VAR ]] is to check if "$VAR" is expanded to null string (""). Thus, [[ -v VAR && -z $VAR ]] should be the correct answer. read more here (with official reference)
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| Aug 4, 2019 at 15:13 | comment | added | Biggybi |
in if [ -n "$VAR" ];, quotes ensure returning 0 for zero-lenght strings.
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| Feb 8, 2017 at 16:01 | comment | added | Jon V |
I feel like your answer requires a caveat - namely if your bash script has something like set -u then the answer will break/fail at that point. There is a subtle (and usually ignored) difference between unset and empty. Note that the distinction is only really important if it's important to you, or if the script has already set -u.
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| S Mar 4, 2015 at 7:19 | history | suggested | Steve Bennett | CC BY-SA 3.0 |
add the important missing half sentence
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| Mar 4, 2015 at 5:30 | review | Suggested edits | |||
| S Mar 4, 2015 at 7:19 | |||||
| Jul 15, 2014 at 13:40 | comment | added | Score_Under |
The double quotes ensure that the variable doesn't get split. A simple $var on a command line will be split by its whitespace into a list of parameters, while "$var" will always be only one parameter. Quoting variables often is a good practice and stops you from tripping up on filenames containing whitespace (among other things). Example: after doing a="x --help", try cat $a - it will give you the help page for cat. Then try cat "$a" - it will (usually) say cat: x --help: No such file or directory. In short, quote early and quote often and you will almost never regret it.
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| Oct 9, 2013 at 5:59 | comment | added | Felipe Alvarez |
the inverse of -z is -n if [ -n "$VAR" ];
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| Jul 22, 2013 at 17:26 | comment | added | Aaron Copley |
if [ ! -z "$VAR" ];
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| Jul 19, 2013 at 23:48 | comment | added | Jürgen Paul |
what's the inverse of -z? if not empty string.
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| Sep 1, 2012 at 1:37 | comment | added | Aaron Newton |
That is true - I was going to recommend -s, but test -s '' exits with a 1, whereas test -z '' gives us the anticipated 0.
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| May 12, 2009 at 18:39 | vote | accept | Brent | ||
| May 12, 2009 at 18:06 | history | answered | duffbeer703 | CC BY-SA 2.5 |