Home / server / Questions / 438194
Accepted
yael
Asked: 2012-10-15 05:05:13 +0800 CST

bash + how to match string that include characters and numbers

  • 772

please advice - what's wrong with my syntax ? ( should not print the "bad interface " )

remark - I work with bash shell

ETH_NAME=eth0         ( or any other as eth1 or eth2 .... )
echo $ETH_NAME

eth0 



[ $ETH_NAME  != eth[0-9] ] && echo bad interface
bash

3 Answers

  1. Best Answer

    Use the [[ ... ]] compound command which can do pattern matching with !=

    $ ETH_NAME=eth0
$ [[ $ETH_NAME != eth[0-9] ]] && echo bad interface
$ ETH_NAME=eth01
$ [[ $ETH_NAME != eth[0-9] ]] && echo bad interface
bad interface
    • 5

  2. Or use the standard (POSIX sh) case statement instead of ksh's [[...]] (also found in bash and zsh).

    case $ETH_NAME in
  (eth[0-9]) ;;
  (*) echo >&2 bad interface
esac

    Note that it will say that eth10 is a bad interface.

    You could instead do

    case $ETH_NAME in
  (eth|eth*[!0-9]*) echo >&2 bad interface;;
  (eth*) ;;
  (*) echo >&2 bad interface
esac

    (note that network interfaces names including ethernet ones are not limited to ethx).

    • 2

  3. My favorite way of doing that matching is case…esac:

    case "$ETH_NAME" in
    eth[0-9]) ;;
    *) echo 'bad interface' ;;
esac

    since it's fast and rather portable (doesn't require using bash). I can't say that subset of regexps available for case is a rich one, but often it's sufficient.

    • 1