replace at the begining

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: replace at the begining by ashish.kvarma (Monk) on Aug 20, 2009 at 12:37 UTC
Another simple solution could be (without using look-behind) `s/<?(p\s+class=)/<$1/;` [download] Regards, Ashish	[reply] [d/l]
Re^2: replace at the begining by Anonymous Monk on Aug 20, 2009 at 15:37 UTC
`#!/usr/bin/perl while(<DATA>){ s/(?<!<)p\sclass=/<p class=/; print $_; } __DATA__ <p class="Hi">Hello <p class="new">How r u` [download] The above output should look like `<p class="Hi"\>Hello <p class="new"\>How r u` [download]	[reply] [d/l] [select]
Re: replace at the begining by Melly (Chaplain) on Aug 20, 2009 at 10:48 UTC
The easiest way is to use a negative class (as noted below by others, this will only work when the error isn't the first thing on the line). `s/[^<]p\sclass=/<p\sclass=/;` [download] Alternatively, use a negative look-behind - (?<!foo): `s/(?<!<)p\sclass=/<p class=/;` [download] Fixed the code - no \s as a replacement `map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2$d$e+$a,$e2 -$d2+$b);$c=$d2+$e2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20` [download] Tom Melly, pm (at) cursingmaggot (stop) co (stop) uk	[reply] [d/l] [select]
Re^2: replace at the begining by $self (Friar) on Aug 20, 2009 at 11:39 UTC
The first solution doesn't work, e.g. when the problem is at the beginning of a line. The negative look-behind does, but character classes don't belong in the replacement string- you can just type the space: `s/(?<!<)p\sclass=/<p class=/;` [download]	[reply] [d/l]
Re^2: replace at the begining by Taulmarill (Deacon) on Aug 20, 2009 at 11:32 UTC
You can't use character classes like `\s` in the replace string, only in the search pattern.	[reply]
Re^2: replace at the begining by Anonymous Monk on Aug 20, 2009 at 11:07 UTC
`s/(?<!<)p\sclass=/<p\sclass=/;` [download] Using of space as '\s' why s is displayed between p and class `<psclass="Hi"> <p class="new">` [download]	[reply] [d/l] [select]
Re^3: replace at the begining by Melly (Chaplain) on Aug 20, 2009 at 11:37 UTC
My mistake - \s means a whitespace character, which can be several things (a space, a tab, etc.). So it makes no sense as a substitution character (of the various options, which should perl use?). `map{$a=1-$_/10;map{$d=$a;$e=$b=$_/20-2;map{($d,$e)=(2$d$e+$a,$e2 -$d2+$b);$c=$d2+$e2>4?$d=8:_}1..50;print$c}0..59;print$/}0..20` [download] Tom Melly, pm (at) cursingmaggot (stop) co (stop) uk	[reply] [d/l]
Re: replace at the begining by sanku (Beadle) on Aug 21, 2009 at 10:02 UTC
hi, The following replacement will be work fine. `while($line=<DATA>){ $line=~s/p\sclass=/<p class=/g; print $line; }` [download]	[reply] [d/l]