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Differences of [ ] and [[ ]] test in bash script

Posted on 2011-09-27
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Last Modified: 2013-12-26
Hello, I would like to understand on which scenario we use [ ] and [[ ]]. What is the the difference between these test operator. Please provide some example to understand it better. Thanks a lot!
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Question by:beer9
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nemws1 earned 1000 total points
ID: 36713002
There's a long description of here it:

  http://mywiki.wooledge.org/BashFAQ/031

Basically, if you have a script with [ as its testing operand, it'll work in bash, sh, ksh, and several other shells.  [[ is more bash specific, but it allows for more fun things (like using "&&" to mean "and" instead of the older style "-a")
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by:farzanj
farzanj earned 1000 total points
ID: 36713503
[ ] is the old way, compatible with old Born.  The newer one is [[ ]] in both Bash and Korn.  With this you can use C++ style operators like ==, <=, &&, || instead of -eq, -le, -a, -o etc and you don't need to use quotations around a variable name.

For mathematical operations, you should use (( )) pair instead.
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