string matching

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

Here is my dilemma:

I need to search for the phrase: !CCSD(T) STATE 1.1 ENERGY in a text file.

simply enough, I can use the matching operator as such:
$_ =~ m/'!CCSD$T$ STATE 1.1 ENERGY'/
The string is matched and all is well.

The complication comes in because I need to read the phrase from a different text file. Once the phrase is parsed from the text, I store it in a variable called $flag.

I, then, use the matching operator this way:
$_ =~ m/$flag/
The string never matches.

I have tried every conceivable combination of quotes and backslashes without any luck. How can I get this rather seemingly routine thing to work?

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Re: string matching by FunkyMonk (Chancellor) on Sep 21, 2007 at 18:27 UTC
Have you tried quotemeta on the pattern you read from a file? There's also a version of quotemeta that works inside your match: `$_ =~ m/\Q$flag/` Update: Are you remembering to chomp the line from the file?	[reply] [d/l] [select]
Re^2: string matching by Anonymous Monk on Sep 21, 2007 at 18:35 UTC
It worked! You are a genius!	[reply]
Re: string matching by kyle (Abbot) on Sep 21, 2007 at 19:09 UTC
FunkyMonk's suggestion of using quotemeta (and `\Q`) should work well. If you really are looking only for literal strings, though, it might be better to use index for that. Also, your original matching pattern contains a dot (`/./`) which will match any character (except newline), so `/1.1/` will also match "`1x1`", for example. You need to quote the dot to make it literal (i.e., `/\./`).	[reply] [d/l] [select]
Re: string matching by Anno (Deacon) on Sep 21, 2007 at 21:26 UTC
You could use `quotemeta()` to make the regex work, as has been noted. Since you are searching for a fixed string, the `index()` function offers itself as a simpler tool that does the job. There is no need to quote anything because `index()` treats all characters equal. `if ( index( $_, $flag) >= 0 ) { # found it` [download] Anno	[reply] [d/l] [select]