Perl regex: matching the first instance of a string after a given match

Question

I'm trying to parse a text file using perl regular expressions. Here's an example data set:

"Field1", "Field2", "Field3", "Field4", "Field5"
"val1-1", "\\path\to\val1-2.txt", "val1-3", "\\path\to\val1-4.ini", "val1-5.txt"
"val2-1", "val2-2", "\\path\to\val2-3.txt", "\\path\to\val2-4.ini", "val2-5.txt"
"\\path\to\val3-1.txt", "val3-2", "val3-3", "\\path\to\val3-4.ini", "val3-5.txt"

For each line of text, I'm trying to match the first instance of .txt file name; the bolded substrings in the above data set.

I thought this would work:

while(<INFILE>) {
    if(m/\\(.*?\.txt)"/) {
        print "$1\n";
    }
}

Output:

\path\to\val1-2.txt
\path\to\val2-3.txt
\path\to\val3-1.txt

but it doesn't because it will match the complete path, not just the filename.

Now this works:

while(<INFILE>) {
    if(my @matches = $_ =~ m/(.*?)"/g) {
        foreach (@matches) {
            print "$1\n" if(m/.*\\(.*?\.txt)/);
        }
    }
}

Output:

val1-2.txt
val2-3.txt
val3-1.txt

But I would suppose there must be a way to do this with a single match expression?

Toto · Accepted Answer · 2014-01-10 09:54:54Z

1

How about:

my $re = qr~\\([^\\"]+)"~;
while(<DATA>) {
    chomp;
    if(my @m = /$re/g) {
        say "@m";
    }
}

__DATA__
"Field1", "Field2", "Field3", "Field4", "Field5"
"val1-1", "\\path\to\val1-2.txt", "val1-3", "\\path\to\val1-4.ini", "val1-5.txt"
"val2-1", "val2-2", "\\path\to\val2-3.txt", "\\path\to\val2-4.ini", "val2-5.txt"
"\\path\to\val3-1.txt", "val3-2", "val3-3", "\\path\to\val3-4.ini", "val3-5.txt"

output:

val1-2.txt val1-4.ini
val2-3.txt val2-4.ini
val3-1.txt val3-4.ini

If you only want the first .txt, do:

my $re = qr~\\([^\\"]+\.txt)~;
while(<DATA>) {
    chomp;
    /$re/ && say $1;
}

answered Jan 10, 2014 at 9:54

Toto

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2 Comments

simbabque Over a year ago

OP said he wants the first .txt, so no need for the .ini I guess. The quoted regex is a good idea though. :)

user3180957 Over a year ago

@simbabque is correct: no need for .ini. Here's how I translated your regex just in case this helps someone else also: [^\\"] ==> match anything that is NOT \ or ". + ==> match at least once. So [^\\"]+\.txt becomes: match any string separated by characters \ or " and whose length is at least one character and ends with .txt.

simbabque · Accepted Answer · 2014-01-10 09:54:58Z

1

Try this one:

while (<DATA>) {
    if(m/([^\\]+\.txt)"/) {
        print "$1\n";
    }
}

__END__
val1-2.txt
val2-3.txt
val3-1.txt

You don't need the \ outside your capture group. Instead, look for everything that's not a backslash instead of just everything. Since you want the file to have a name in front of the .txt you want the + quantifier, not the *? which is match something or nothing but get as few as possible.

answered Jan 10, 2014 at 9:54

simbabque

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