correct usage of q, quotemeta, with s///

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

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Re: correct usage of q, quotemeta, with s/// by I0 (Priest) on May 31, 2002 at 00:58 UTC
`$page =~ s/\Q$old_text\E/$new_code/g;`	[reply] [d/l]
Re: correct usage of q, quotemeta, with s/// by Joost (Canon) on May 31, 2002 at 09:36 UTC
You must use some kind of quoting before you can use arbitrary strings in a regex, otherwise the special characters are interpreted as regex constructs instead of regular substrings. As noted above, you can use either the \Q...\E construct or quotemeta() - it works something like this: `my $string = 'abc!hu('; print "\Q$string\E\n"; # prints abc\!hu\( print quotemeta $string; # prints abc\!hu\(` [download] The \Q .. \E construct is a little easier in this case, because you can embed it in your match - you should not use it in the replacement part of a substitution, because that's (a lot like) a regular double-quoted string: `s/\Q$string\E/$replacement/; # or .. $qstring = quotemeta $string; s/$qstring/$replacement/;` [download] For (a lot more) info, take a look at `perldoc perlre perldoc perlop (the m// part)` [download] </code> `-- Joost downtime n. The period during which a system is error-free and immune from user input.` [download]	[reply] [d/l] [select]
Re: correct usage of q, quotemeta, with s/// by termix (Beadle) on May 30, 2002 at 22:36 UTC
You have a single space before and a single space after both the strings. Is that a required effect? Notice: `my $page="nospaceLOTSnospace space LOTS space"; my $old_text = qq ( LOTS ); my $new_text = qq ( LESS ); $page =~ s/$old_text/$new_text/g; print $page;` [download] ... will output ... `nospaceLOTSnospace space LESS space` The first "LOTS" does not get replaced because you are replacing " LOTS " (space before and after) with " LESS " -- termix	[reply] [d/l] [select]
Re: Re: correct usage of q, quotemeta, with s/// by cidaris (Friar) on May 30, 2002 at 23:52 UTC
The spacing is irrelevant, (perhaps I should have noted that) I simply used it for illustration purposes. "LOTS" simply indicates several lines of HTML that include double-quotes, slashes, you name it. (Note: several lines) `my $page` is also several lines of HTML, the contents of an entire file, actually. I'm trying to replace multiple lines of code (compressed into a single string) in one big string (the entire file) with another string (more lines of code). I hope this is somewhat clearer.	[reply] [d/l]


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