05-06-2011
Difference between [condition] and [[condition]] and ((condition)) when used with if condition
Executed the following if conditions .. and got different results .
only (( )) gave correct o/p with all scenarios .
Can anybody please let me know what is the difference between [condition] and [[condition]] and ((condition)) when used with if condition.
And why each condition gave different result.
1.
if [ 234 > 71 ];then
echo "correct"
else
echo "wrong"
fi
O/p : correct
2.
$if [[ 234 > 71 ]];then
echo "correct"
else
echo "wrong"
fi
o/p : wrong
3.
if [[ 234 > 700 ]];then
echo "correct"
else
echo "wrong"
fi
o/p : wrong
4.
if [ 234 > 700 ];then
echo "correct"
else
echo "wrong"
fi
o/p : correct
5.
$if (( 234 > 700 ));then
echo "correct"
else
echo "wrong"
fi
o/p : wrong
6.
if (( 234 > 71 ));then
echo "correct"
else
echo "wrong"
fi
o/p : correct
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echo(1B) SunOS/BSD Compatibility Package Commands echo(1B)
NAME
echo - echo arguments to standard output
SYNOPSIS
/usr/ucb/echo [-n] [argument]
DESCRIPTION
echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output.
echo is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi-
ronment variables.
For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows:
o echo your current-working-directory's full pathname
o pipe the output through tr to translate the path's embedded slash-characters into space-characters
o pipe that output through wc -w for a count of the names in your path.
example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w"
See tr(1) and wc(1) for their functionality.
The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be invoked if
the user calls echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape
characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the black-slashed escape characters, and ksh's
echo() also understands a as the audible bell character; however, these commands do not have an -n option.
OPTIONS
-n Do not add the NEWLINE to the output.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWscpu |
+-----------------------------+-----------------------------+
SEE ALSO
csh(1), echo(1), ksh(1), sh(1), tr(1), wc(1), attributes(5)
NOTES
The -n option is a transition aid for BSD applications, and may not be supported in future releases.
SunOS 5.10 3 Aug 1994 echo(1B)