hello

I want to do a pattern match for string in the if statement, but I am not sure how to use regex inside the if statement.

I am looking for something like this:

if [ $name = [ab]{2,3} ]; then
.....
....
...
fi

One possible solution:

if echo $name | grep -Eq '[ab]{2,3}'
then
    echo 'Yesss!'
fi

Hi.

If you can use bash3, then the "=~" operator and "[[" "]]" can be used with regular expressions.

However, a method that would work with all Bourne-family shells would be:

if echo "$VARIABLE" | grep "regular-expression"
then
  echo Success
else
  echo Failure
fi

but this prints the grep result. I tried to redirect the output to /dev/null but then if fails. Is there a way I can avoid the grep result on stdout?

Using a case/esac statement makes regular expressions simple and obvious.

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

Hi.
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:

#!/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: http://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

% ./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

Yes, it's globbing, not re's.
For {2,3} with globbing:

bash 3.2.25(1)$ v=b
bash 3.2.25(1)$ case $v in ([ab][ab]|[ab][ab][ab]) echo OK;;(?) echo KO;;esac
KO
bash 3.2.25(1)$ v=bbb
bash 3.2.25(1)$ case $v in ([ab][ab]|[ab][ab][ab]) echo OK;;(?) echo KO;;esac
OK
bash 3.2.25(1)$ # or:
bash 3.2.25(1)$ shopt -s extglob
bash 3.2.25(1)$ v=b
bash 3.2.25(1)$ case $v in ([ab][ab]?([ab])) echo OK;;(?) echo KO;;esac
KO
bash 3.2.25(1)$ v=bb
bash 3.2.25(1)$ case $v in ([ab][ab]?([ab])) echo OK;;(?) echo KO;;esac
OK