Re: comparing string with regular expression using test command in unix

[Eric Blake]

> 
> Hi,
> 
> I want to compare a variable holding *string* with the *regular 
> expression *. Is it possible to do in unix with a single command?
> Can we use "test" command in UNIX to compare a *string *with the 
> *regular expression*? if so please provide an example for that.

This sort of question generally implies that it would be well
worth your investment in a good book on Unix shell programming.

In coreutils, 'info expr' may prove enlightening.  For example,

$ foo=bar
$ expr $foo : 'ba*' && echo found || echo not found
2
found
$ expr $foo : 'ca*' && echo found || echo not found
0
not found

Outside of the realm of coreutils, there are other
techniques.  For example, in /bin/sh, you can do glob
matching (instead of regular expressions) like this:

$ case $foo in ba*) echo found ;; *) echo not found ;; esac
found

Or use the regular expressions in sed:

$ echo $foo | sed -ne '/ba*/p'
bar
$ echo $foo | sed -ne '/ca*/p'
$

Or several other ideas.  Hopefully this gives you some ideas.

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--
Eric Blake