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Re: backrefs in regexps?


From: Tim Nelson
Subject: Re: backrefs in regexps?
Date: Tue, 19 Oct 2004 14:01:00 +1000 (EST)

On Tue, 19 Oct 2004, martin f krafft wrote:

Hi all, I am new to cfengine and thus, this may be a really dumb
question. However, I went through the docs and I could not find the
solution, honestly.

I am trying to use editfiles/ReplaceAll and backreference into the
search pattern, conceptually like so:

 ReplaceAll "foo(.*)bar" With "bar$1foo"

However, the $1 is replaced literally. Is there a way to do what
I want/need?

Looking at this and your other question, you need to carefully learn the differences between the three different types of Regex. They are:

-       Basic (POSIX) Regex
-       Extended (POSIX) Regex
-       Perl Regex

Basic Regex is the one used by most Unix utilities such as grep. Extended is supported by most of the same utilities (grep -E, or egrep). Perl regex is only supported by some tools (eg. Perl, the pcre library, PHP, and some others). You'll notice that the cfengine Reference manual says "The regular expression matching functions are POSIX extended regular expressions". For more information:

http://en.wikipedia.org/wiki/Regular_expression

        Anyway, to come back to your problem...

In this e-mail, you may find that it works if you use \1 instead of $1. If not, you'll need to do some more reading.

In your other e-mail, you'll find that \s doesn't exist in eregex. You could use [[:space:]] (elegant but long-winded) or [ \n\t] (and maybe \r too).

        Hope this helps...

--
Tim Nelson
Server Administrator
WebAlive Technologies Global
Level 1 Innovation Building, Digital Harbour
1010 LaTrobe Street
Docklands, Melbourne, Vic, 3008
Phone: +61 3 9934 0812
Fax: +61 3 9934 0899
E-mail: address@hidden
http://www.webalive.biz/




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