php PCRE regex to get only the file name that terminates in .txt

Question

so I am trying to form a PCRE regex in php, specifically for use with preg_replace, that will match any number of characters that make up a text(.txt) file name, from this I will derive the directory of the file.

my initial approach was to define the terminating .txt string, then attempt to specify a character match on every character except for the / or \\, so I ended up with something like:

'/[^\\\\/]*\.txt$/'

but this didn't seem to work at all, I assume it might be interpreting the negation as the demorgan's form aka: (A+B)' <=> A'B'

but after attempting this test:

'/[^\\\\]\|[^/]*\.txt$/'

I came to the same result, which made me think that I shouldn't escape the or operator(|), but this also failed to match. Anyone know what I'm doing wrong?

Answer 1

The foloowing regular expression should work for getting the filename of .txt files:

$regex = "#.*[\\\\/](.*?\.txt)$#";

How it works:

• .* is greedy and thus forces match to be as far to the right as possible.
• [\\\\\\\\/] ensures that we have a \\ or / in front of the filename.
• (.*?\\.txt) uses non-greedy matching to ensure that the filename is as small as possible, followed by .txt , capturing it into group 1.
• $ forces match to be at end of string.

Answer 2

Try this pattern '/\\b(?P<files>[\\w-.]+\\.txt)\\b/mi'

$PATTERN = '/\b(?P<files>[\w-.]+\.txt)\b/mi';
$subject = 'foo.bar.txt plop foo.bar.txtbaz foo.txt';
preg_match_all($PATTERN, $subject, $matches);
var_dump($matches["files"]);