Generally we like to see a little effort rather than "write this code for me". Show us what you have tried so far. If you haven't tried anything take a look at the Tutorials section here and at the Pattern Matching, Regular Expressions, and Parsing section in particular. You should also look at perlretut, perlrequick, perlre and perlreref.

If you still have trouble after that come back with your attempted code and ask again.

"..how can i write a regular expressions for this .."

If you wish to learn about regular expressions, then probably the two best places to start are with perlre and perlretut.

If you are really serious about learning regular expressions, then you'll be wanting a copy of the Owl.

Cheers,
Darren

thanks for your advise me, i will follow you to learnning regular expressions

If you really want to use a regular expression for this, it would be something like /^.*?=(.*)$/. After that regex, $1 would hold your ID.

A regular expression isn't the right tool for that. Regular expressions can be expensive in terms of efficiency. So, you should favor other methods when possible.

For those strings use split ...

use strict;
use warnings;
my @strings = (
    "http://mysite/bbsui.jsp?id=dxpwd",
    "http://mysite/bbsui.jsp?id=dxpsf",
    "http://mysite/bbsui.jsp?id=sfpwd",
    "http://mysite/bbsui.jsp?id=ds35e",
    "http://mysite/bbsui.jsp?id=124536"
);

for ( @strings ) {
    my ($base, $id) = split( /=/, $_, 2 );
    print "Id: $id\n";
}
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--
-- Ghodmode

FWIW, these are my most frequently used resources for constructing/understanding regexes:

Mastering Regular Expressions
perlrequick
perlretut
perlre
YAPE::Regex::Explain
GraphViz::Regex
The Regex Coach (Win32 only, IIRC)

HTH,

use strict;
use warnings;
my @strings = (
    "http://mysite/bbsui.jsp?id=dxpwd",
    "http://mysite/bbsui.jsp?id=dxpsf",
    "http://mysite/bbsui.jsp?id=sfpwd",
    "http://somewhere.else.jsp?id=YOU-DO-NOT-WANT-THIS",
    "http://mysite/bbsui.jsp?id=ds35e",
    "http://somewhere.else.too?id=XXXXXXXXXXXXXXXXXXXX",
    "http://mysite/bbsui.jsp?id=124536"
);

my $base = 'http://mysite/bbsui.jsp?id=';
my $pattern = "^\Q$base\E(.+)\$";
my @id = grep { $_ } map { $1 if /$pattern/ } @strings;
print  "(" . join (',', @id) .")\n";
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(dxpwd,dxpsf,sfpwd,ds35e,124536)
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thanks very much

Is that ur home work ?

update ..

use strict;
use warnings;
my @strings = (
    "http://mysite/bbsui.jsp?id=dxpwd",
    "http://mysite/bbsui.jsp?id=dxpsf",
    "http://mysite/bbsui.jsp?id=sfpwd",
    "http://mysite/bbsui.jsp?id=ds35e",
    "http://mysite/bbsui.jsp?id=124536"
);

for ( @strings ) {
    my ($id) = split( /=/, $_)[1];
    print "Id: $id\n";
}
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$xyz = "http://mysite/bbsui.jsp?id=dxpwd";
$id = $1 if ($xyz =~ m/\?id=(.+?)$/i);
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