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Is there any difference in bash shell in [ .. ] and [[ .. ]] ?

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# 1  
Old 07-02-2008
Is there any difference in bash shell in [ .. ] and [[ .. ]] ?
Could someone tell me if there is any difference in using square brackets single or doubled pair?

So, do those two some how could be treted by shell differently:
Code:
if [ <condition> ] ; then <statements;> else <statements;> fi

and
Code:
if [[ <condition> ]] ; then <statements;> else <statements;> fi

Maybe any one could provide with any additional shell usage compare to another?

Thank you,
Alex
# 2  
Old 07-02-2008
If you use "[.....]" you are actually using /bin/test (/bin/[). Try man [ and you will get the test(1) manpage.

If you use [[.....]] you are using bash's builtin test . Using a builtin is faster and more efficient since no fork/exec is required.
# 3  
Old 07-02-2008
These days they are both built-ins:

Code:
$ echo $BASH_VERSION
3.2.39(19)-release
$ type [
[ is a shell builtin
$ type [[
[[ is a shell keyword
$

[ is included mostly for backward compatibility to Bourne shell and the /usr/bin/test that fpmurphy mentioned. I usually prefer the syntax of [[.
# 4  
Old 07-03-2008
Thank you, guys for reply!
So, from user point of view there is no difference in usage [ ... ] or [[ ... ]]?
Is it correct?

Having by today both as a part of shell (buildin and keyword) now it is really hard to say witch one could be more efficient, right?
# 5  
Old 07-03-2008
See The UNIX Forums - View Single Post - Shell basics
# 6  
Old 07-03-2008
For portability use [.....] . For efficiency, use [[.....]]
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