> So \w means the first non word character. What about the ~ / before
> the
> (\w? And what does the + sign do? Is $buf a command?
Although I do not claim to be an expert, nor do I play one on TV, I'll
give a try at this one. Here's the command that was given to you:
($acct) = $buf =~ /(\w+)/;
$buf, in this case is the line you want to extract your user from. You
have a file, with lines such as the following:
<[EMAIL PROTECTED]> SIZE=1024
and you extract each of these lines at a time into $buf (after opening
the file of course).
while ($buf = <FILE>) {
# $buf now contains line of file, one per each loop of while
$buf =~ /(\w+)/;
$userName = $1;
...do something with $userName
}
Now, to answer the remaining questions. =~ is the 'pattern match'
operator. It's what actually fetches the first word pattern (user).
Likewise, !~ says 'do not match'.
When 'user' is extracted, it is put into special variable $1. This is
what the parenthesis does.
The '+' operator says 'get one or more word characters [A-Za-z0-9_]
until we run out of word characters to capture'. '+' is what is known
as a greedy operator. It will grab things until it can't get any more
(or until it has to save enough data in the $buf variable for further
regex's to match, which is not the case here). This means that it
looks past the first '<', and reads up until the next non-word char,
'@', returning 'user' (w/o quotes).
Read:
perldoc perlop
perldoc perlretut
perldoc perlre
I HTH, and I surely hope that I've been reasonably accurate with my
assessment.
Steve
>
> Thanks
>
> AD
>
> -----Original Message-----
> From: Bob Showalter [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, October 19, 2004 8:57 AM
> To: 'Khairul Azmi'; [EMAIL PROTECTED]
> Subject: RE: simple regular expression problem
>
> Khairul Azmi wrote:
>> Hi all,
>> I am a newbie. I just need to extract the string containing the unix
>> account from the following text
>>
>> <[EMAIL PROTECTED]> SIZE=1024.
>
> I'm guessing you want to extract the string "user"? (But how do you
> know
> that that corresponds to a Unix account?)
>
> The following will catpure "user" from the example you gave:
>
> ($acct) = $buf =~ /(\w+)/;
>
> This works because:
>
> a) \w matches 'u', 's', 'e', and 'r', but not '<' or '@'
> b) regexes match the "longest, leftmost" sequence, so
> 'user' matches instead of 'gmail'.
>
> You would be advised to replace \w with the actual class of characters
> that
> are allowed in user names...
>
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>
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