Regular Expression - "\" chars at the end of the string

sbd!

I had a problem with string which have some \ chars at the end of the
string. For example:

$String = "I want this **** out of here\\\\\\\\\";

I needed to remove it useing regular expression...i thinked that
something like "/\\+$/" is enough but i was wrong. I made some tries
and finaly i removed "\" chars it with "/\\\+$/". It works (i'm proud
with myself :)), but i can't understand why \\\ matchs single \, and \\
not...

Jul 17 '05 #1

Jan Pieter Kunst

sbd! wrote:

I had a problem with string which have some \ chars at the end of the
string. For example:

$String = "I want this **** out of here\\\\\\\\\";

I needed to remove it useing regular expression...i thinked that
something like "/\\+$/" is enough but i was wrong. I made some tries
and finaly i removed "\" chars it with "/\\\+$/". It works (i'm proud
with myself :)), but i can't understand why \\\ matchs single \, and \\
not...

Because (as far as I understand it) backslashes have to be escaped
twice: once for the regular expression engine, and once for PHP.

JP

--
Sorry, <de*****@cauce.org> is a spam trap.
Real e-mail address unavailable. 5000+ spams per month.

Jul 17 '05 #2

Matt Mitchell

"Jan Pieter Kunst" <de*****@cauce.org> wrote in message
news:42***********************@news.xs4all.nl...
: sbd! wrote:
: > I had a problem with string which have some \ chars at the end of the
: > string. For example:
: >
: > $String = "I want this **** out of here\\\\\\\\\";
: >
: > I needed to remove it useing regular expression...i thinked that
: > something like "/\\+$/" is enough but i was wrong. I made some tries
: > and finaly i removed "\" chars it with "/\\\+$/". It works (i'm proud
: > with myself :)), but i can't understand why \\\ matchs single \, and \\
: > not...
: >
:
: Because (as far as I understand it) backslashes have to be escaped
: twice: once for the regular expression engine, and once for PHP.

One way to get round this is to use single quotes instead:

'/\\+$/' gets round the esacaping problem. Don't double-quote PREG strings,
it gives you no end of trouble!

If you have to interpolate variable values into perl regexes, have a look at
http://php.net/preg_quote

Matt

Jul 17 '05 #3

John Dunlop

Jan Pieter Kunst wrote:

: Because (as far as I understand it) backslashes have to be escaped
: twice: once for the regular expression engine, and once for PHP.
Matt Mitchell wrote:
One way to get round this is to use single quotes instead:

'/\\+$/' gets round the esacaping problem.

No, you still need to escape the backslash twice.

That pattern matches the same as "/\\+$/"; that is, a plus
sign at the end of the subject string or before a newline at
the end. Only one backslash is passed to the regular
expression engine, so the plus sign no longer carries its
special meaning as a quantifier.

http://www.php.net/manual/en/language.types.string.php

--
Jock

Jul 17 '05 #4

sbd!

Thank you! All answers are helpful!

Jul 17 '05 #5

Matt Mitchell

"John Dunlop" <us*********@john.dunlop.name> wrote in message : >
: > '/\\+$/' gets round the esacaping problem.
:
: No, you still need to escape the backslash twice.
:

Whoops, not thinking before posting again...

<g>
Matt

Jul 17 '05 #6