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Top Forums UNIX for Dummies Questions & Answers Regex in if-then-else statement to match strings Post 302136793 by drl on Wednesday 19th of September 2007 06:01:03 PM
Old 09-19-2007
Hi.
Quote:
Originally Posted by porter
Using a case/esac statement makes regular expressions simple and obvious.

Code:
case $name in
    [ab]{2,3} )
         echo do stuff
         ;;
    * ) 
         ;;
esac

Perhaps I am using a too-old version of bash. Version 3.00.16(1) recognizes the [ab] but not the {2,3} part, apparently because the case selectors are expanded in the same fashion as pathnames, not regular expressions:
Code:
#!/bin/bash3

# @(#) s4       Demonstrate case selectors.

set -o nounset
echo

echo "GNU bash $BASH_VERSION" >&2
echo " MUST USE VERSION 3 FOR REGULAR EXPRESSIONS WITH =~ OPERATOR!"
# See: https://www.unix.com/showthread.php?p=302136557&posted=1#post302136557

echo

# if [ $name = [ab]{2,3} ]; then
name="b"
name="bb"
echo " Original string = \"$name\""

case $name in
[ab]{2,3} )
    echo Success
        ;;
* )
    echo Failure
        ;;
esac

echo
name="b{2,3}"
echo " Original string = \"$name\""

case $name in
[ab]{2,3} )
    echo Success
        ;;
* )
    echo Failure
        ;;
esac

exit 0

producing:
Code:
% ./s4

GNU bash 3.00.16(1)-release
 MUST USE VERSION 3 FOR REGULAR EXPRESSIONS WITH =~ OPERATOR!

 Original string = "bb"
Failure

 Original string = "b{2,3}"
Success

... cheers, drl
 

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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)
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