Berkeley CSUA MOTD:Entry 50557
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2018/04/25 [General] UID:1000 Activity:popular
4/25    

2008/7/14-16 [Computer/SW/Languages/Perl, Computer/SW/Unix] UID:50557 Activity:moderate
7/14    Shell Programming question: I want to call a script with 1 arg
        and have it figure out whether $1 is a MAC address or an IP address
        and then do call the appropriate function.  What is the best way
        to do this, given that sh/bash/ksh do not have something like
        the =~ in perl.  Check for exit status of grep, or is there a
        a better way?  For the moment, let's just say the two tests are:
          echo $1 | fgrep : > /dev/null && echo isMAC || echo notMAC
          echo $1 | fgrep . > /dev/null && echo isIP || echo notIP
          and if neither, then Usage()
        I want to avoid requiring the user to either do "-i IP" or "-m MAC".
        Note: this doesn't have to do extensive syntax checking ... it's
        not a security application.  Just trying to save typing.
        \_ You may want to recheck your assumption of bash not having =~.
           \_ Thanks for that information.  I didn't know know about that.
              Although right now it is in sh.  Any portable pure sh ideas?
              I'm really interested in what is the "right" way to do this,
              rather than just coming up with something which works.
              \_ "right" depends on your situation. If you actually need
                 to support old systems, or be portable across many systems,
                 then maybe you should stick with sh. If you know your
                 audience is all going to have bash or whatever (and that
                 is not at all unlikely these days), then I see no good
                 reason to suffer under older, less capable tools.
              \_ Dude, it's a sh script.  If it works, it works.  Seriously.
                 Stick it in a function if it looks too ugly and then forget
                 about it.  If you need something to be maintainable or
                 it's a called enough there is any concern about it being
                 too slow you are going to have to bite the bullet and use
                 a reasonable scripting language.  Otherwise just make it work
                 and move on to something that is worth spending time on.
              \_ I think "right" in this case, means readable and maintainable
                 by the next poor guy that has to come along. Just document
                 your code and you will be fine.
              \- I think one way to distill the question is "how do i get =~
                 in sh" ... would you do "echo $string | egrep <regexp>" + $?
                 to get exit status of the grep ... I think the case approach
                 below is nice and clean as long as you are ok with something
                 like *:*:*:*:*:* for MACs and *.*.*.* for IPs, and dont need
                 "true" regexps.
                 "true" regexps. I wouldnt use awk to test, but maybe if you
                 need to mangle.
        \_ Why would you do this in a shell progam?
        \_ use case:

        found="NO"
        case "$1" in
             *:*)    echo "isMAC"; found="YES";;
             *.*)    echo "isIP"; found="YES";;
             *)      if [ "$found" = "NO" ] ; then
                        echo "NOT MAC" ; echo "NOT IP";
                     fi
                     ;;
        esac
2018/04/25 [General] UID:1000 Activity:popular
4/25    

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