Single or double square brackets Post: 302708191

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Top Forums UNIX for Dummies Questions & Answers Single or double square brackets Post 302708191 by elixir_sinari on Monday 1st of October 2012 07:31:20 AM

10-01-2012

Registered User

Quote:

Originally Posted by pamu

Use quotes around it, so you can avoid variable expansion in shell.

What is that, pamu?
Variable expansion will be done by the shell in any case (in case of double-quotes). The double-quotes are to retain the embedded spaces and/or to tell the shell that the parameter exists (in case of null strings) in case of [..] construct.
You don't require the quotes in case [[..]] construct (unless you are testing strings as is).
Also, in the [[..]], globbing is not done.

In ksh88,

Code:

$ [ -z $x ] && echo HI
ksh: test: 0403-004 Specify a parameter with this command.

$ [ -z "$x" ] && echo HI
HI

$ [[ -z $x ]] && echo HI
HI

$ ls *test*
testftp
test.pl
testawk
testsed
testfile
test
testxml

$ [ -e *test* ] && echo HI || echo BYE
HI

[[ -e *test* ]] && echo HI || echo BYE
BYE

Last edited by elixir_sinari; 10-01-2012 at 08:38 AM..

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