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Old 09-30-2013, 03:47 PM   #1
anandg111
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when to use ( ), [ ] and [[ ]][ in " if "


when to use ( ), [ ] and [[ ]] in " if "
 
Old 09-30-2013, 06:46 PM   #2
Firerat
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http://www.tldp.org/LDP/Bash-Beginne...ect_07_02.html

Quote:
[] vs. [[]]

Contrary to [, [[ prevents word splitting of variable values. So, if VAR="var with spaces", you do not need to double quote $VAR in a test - eventhough using quotes remains a good habit. Also, [[ prevents pathname expansion, so literal strings with wildcards do not try to expand to filenames. Using [[, == and != interpret strings to the right as shell glob patterns to be matched against the value to the left, for instance: [[ "value" == val* ]].
(()) is for numbers [[]] strings

[[ ]] can be used for number comparison, but you should not

Code:
Foo=foo # a string
if [[ $Foo -lt 10 ]]
then
    echo $Foo is less than 1
fi
^^^ bad, your script might not do what you expect it to do

Last edited by Firerat; 09-30-2013 at 06:49 PM.
 
  


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