Why is [[ ]] different then [ ]? Post: 302280829

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Top Forums Shell Programming and Scripting Why is [[ ]] different then [ ]? Post 302280829 by 2dumb on Tuesday 27th of January 2009 03:53:29 PM

01-27-2009

Registered User

Why is [[ ]] different then [ ]?

Please tell me why this outcome is different in a if statement. Some times I can use [ ] and its fine other times I need to use [[ ]].

Script:
#!/usr/bin/sh
CHECK1=`ps -ef | grep -v grep | grep lkdflkdfhdlkf | awk '{print $2}'`
if [ -n ${CHECK1} ]
then
echo "found"
else
echo "not found"
fi
Output:
./test.sh
./test.sh[3]: test: 0403-004 Specify a parameter with this command.
not found

Script:
#!/usr/bin/sh
CHECK1=`ps -ef | grep -v grep | grep lkdflkdfhdlkf | awk '{print $2}'`
if [[ -n ${CHECK1} ]]
then
echo "found"
else
echo "not found"
fi
Output:
./test.sh
not found

2dumb

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LEARN ABOUT OPENDARWIN

zgrep

ZGREP(1)						      General Commands Manual							  ZGREP(1)

NAME

       zgrep - search possibly compressed files for a regular expression

SYNOPSIS

       zgrep [ grep_options ] [ -e ] pattern filename...

DESCRIPTION

       Zgrep  is used to invoke the grep on compress'ed or gzip'ed files. All options specified are passed directly to grep.  If no file is speci-
       fied, then the standard input is decompressed if necessary and fed to grep.  Otherwise the given files are uncompressed	if  necessary  and
       fed to grep.

       If  zgrep  is invoked as zegrep or zfgrep then egrep or fgrep is used instead of grep.  If the GREP environment variable is set, zgrep uses
       it as the grep program to be invoked. For example:

	   for sh:  GREP=fgrep	zgrep string files
	   for csh: (setenv GREP fgrep; zgrep string files)

AUTHOR

       Charles Levert (charles@comm.polymtl.ca)

SEE ALSO

       grep(1), egrep(1), fgrep(1), zdiff(1), zmore(1), znew(1), zforce(1), gzip(1), gzexe(1)

																	  ZGREP(1)