UNIX for Dummies Questions & Answers

Quite possibly a simple problem who's answer is evading me:

I am trying to write a sh shell script, part of which is *logically* trying to do the following:

if [ $1 = [A-Za-z] ]; then
...
fi

if [ $1 = [0-9.] ]; then
...
else
...
fi

Where the 1st condition is looking for a hostname passed as $1, the second a dotted-quad ip address, and the 3rd a catch-all error condition.

I cannot work out how to use regex with the test ([) command. Would $1 always evaluate to "TRUE"? And therefore I would use something like:

if [ $1 -a regex ]; then
...
fi

or not?
BTW: I know the regex I have given in the example are not water-tight for their application ([0-9.] doesn't necessarily guarantee a dotted-quad by any means), this is a tool which is only going to be used by myself, and therefore isn't too much of a problem

If someone would like to supply the regex for a dotted quad I would be most greatful :-), but no sweat.

Thanks in advance.

Is this the correct regex for a dotted-quad IP address?

[0-9]\{1,3\}\.\{1\}[0-9]\{1,3\}\.\{1\}[0-9]\{1,3\}\.\{1\}[0-9]\{1,3\}

In ksh you can use patterns...

Code:

if [[ $1 = +([0-9]).+([0-9]).+([0-9]).+([0-9]) ]] ; then
   echo $1 is an ip address
else
   echo $1 is not an ip address
fi

stright from Mastering Regular Expresstions by Oreilly page 124

Code:

^([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.
([01]?\d\d?|2[0-4]\d|25[0-5])\.([01]?\d\d?|2[0-4]\d|25[0-5])\.$

this should all be on 1 line btw. the reason 0-9 wont work as mentioned above it cuz if you want a ligit ip all the time 0-9 wont work. remember 0-9 says even an ip of 999.999.999.999 is valid when we all know is not valid in any universe (yet anyways).

btw this book is a book i think everyone that is into unix, programing, scripting should read.

the hostname check is on page 167