What are these "keys" in bash script?

Question

I'm interested in:

if [ -z "${var// }" ]...

if [ -d $dir ]...

More precisely, what is -z and -d? How can I call it and where can I read about this "keys"? And where can i find a full list of this "keys"?

try the documentation: `man bash` – jdigital Nov 05 '17 at 04:50 — jdigital, Nov 05 '17 at 04:50

score 1 · Answer 1 · answered Nov 05 '17 at 04:50

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Look at the manpage for test

man test

answered Nov 05 '17 at 04:50

Rob Hales

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Or `help test` for the built-in `test`. :-) – anishsane Nov 05 '17 at 06:01
or `man [`, since "[" is actually the command being used here (which happens to be synonymous with the `test` command). – Gordon Davisson Nov 05 '17 at 06:02

score 1 · Accepted Answer · answered Nov 05 '17 at 04:53

-z variable will check condition if a variable is NULL then the condition will be TRUE if NOT then it will go to else part of if condition.

-d directory_name will check if a directory name which is given next to it is present or not. If directory is present then condition will be TRUE or it will be FALSE.

From man test

-z STRING

the length of STRING is zero

-d FILE

FILE exists and is a directory

score 1 · Answer 3 · answered Nov 05 '17 at 05:00

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in bash manual invoked using

 man -a bash

a section called CONDITIONAL EXPRESSIONS which covers what you are looking for, in fact there are a whole bunch of basic to advanced concepts in there to look for.

answered Nov 05 '17 at 05:00

asio_guy

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What are these "keys" in bash script?

3 Answers3