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 
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3 Answers
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 answered Oct 14, 2012 at 13:15
- 1Another option would be a regular expression:
[[ ! $ETH_NAME =~ ^eth[0-9]$ ]]Ansgar Wiechers– Ansgar Wiechers2012-10-14 13:20:30 +00:00Commented Oct 14, 2012 at 13:20 - 2@AnsgarWiechers: Yes, but you still need to use
[[rather than[which is what the OPs problem was.user9517– user95172012-10-14 13:48:41 +00:00Commented Oct 14, 2012 at 13:48 - I didn't claim anything different.Ansgar Wiechers– Ansgar Wiechers2012-10-14 13:56:31 +00:00Commented Oct 14, 2012 at 13:56
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).
- This one is my favorite, since it's fast and
/bin/sh-compatiblepoige– poige2012-10-14 14:57:44 +00:00Commented Oct 14, 2012 at 14:57 - Note that it's not
/bin/shcompatible (as some/bin/shlike the Bourne shell still found on some systems are not POSIX and don't accept that syntax) but it is POSIX sh compatible so would work in any POSIX conformant shell.sch– sch2012-10-14 15:49:00 +00:00Commented Oct 14, 2012 at 15:49 - Actually it is, but I have no idea why you use opening
(. Every manual from BSD's till Solaris have mentions ofcase…esacbut usespattern) listsyntax.poige– poige2012-10-14 16:37:26 +00:00Commented Oct 14, 2012 at 16:37 - Yes, the leading "(" is POSIX but not Bourne. It is more legible, helps with bracket matching in vi, avoid parsing issues in some shells inside
$(...). It is supported by all POSIX shells and IIRC the Almquist shell (even the original one before it was made POSIX), so basically all Bourne-like shells but the Bourne shell. It breaks Bourne compatibility.sch– sch2012-10-14 19:13:23 +00:00Commented Oct 14, 2012 at 19:13 - Ok, bracket matching is cool thing, but ability to not require
/bin/bashand be more portable is of a higher importance (as to me). )poige– poige2012-10-14 19:18:03 +00:00Commented Oct 14, 2012 at 19:18
My favorite way of doing that matching is case…esac:
case "$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.
