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# 1  
Old 10-01-2012
Single or double square brackets

Hi frieds, I don't understand the difference between single square bracket and double square brackets in a IF condition.

Ex.
Code:
if [$ESEGUI == "SI" &&  $Ora -ge $TimeOverRun];
then
   RETURNJOB=1
else
   RETURNJOB=0
fi

It run, but this
Code:
if [[$ESEGUI == "SI" &&  $Ora -ge $TimeOverRun]];
then
   RETURNJOB=1
else
   RETURNJOB=0
fi

don't run and this
Code:
if [[ $ESEGUI == "SI" ]]; then
    /opt/orsyp/UNIV56/exp/script/runjobnagios_header_20120727.ksh $FLUSSO $SP $ReportPath $DBNAME $DBUSER $DBPASSWORD $PROJECT
   RETURNJOB=$?
else
   RETURNJOB=0
fi

run!

I don't understand why.

Can you help me to understand it?

Thanks
Moderator's Comments:
Mod Comment Please use code tags

Last edited by jim mcnamara; 10-01-2012 at 08:23 AM..
# 2  
Old 10-01-2012
First whenever you are using square brackets.
Use space in between square brackets and conditions.
Use quotes around it..

Code:
if [ "$ESEGUI" == "SI" && "$Ora" -ge "$TimeOverRun" ];

#and

if [[ $ESEGUI == SI && $Ora -ge $TimeOverRun ]];


Last edited by pamu; 10-01-2012 at 08:44 AM..
# 3  
Old 10-01-2012
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..
This User Gave Thanks to elixir_sinari For This Post:
# 4  
Old 10-01-2012
Quote:
Originally Posted by elixir_sinari
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

Oppss. Smilie.. i think i have misread and misplaced another concept here..... need to correct.. thanks...Smilie

but in bash

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

# 5  
Old 10-01-2012
in bash try:
Code:
type [
type [[

They are both part of the shell: [ is a keyword like if, while, etc.: [[ is a shell builtin but still is treated a a word.

"word" is key here, because words are set off from each other by spaces or new lines.
[, ], [[, and ]] have to be set off from from other words by spaces or new lines.
This User Gave Thanks to jim mcnamara For This Post:
 

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