CODEWITHSUNDEEP
regex
Lukie
Lukie

Reputation: 905

RegEx filename Exclusion match

I've seen other posts on SO for RegEx matches excluding strings (using negative look ahead / look behind) but i'm still having a hard time getting it to work. Was hoping someone could help.

I have a RegEx

\.(gif|jpg|png)$

Which i use to match any filenames ending in (gif/jpg/png)

However i want to use an exclusion list so that certain file names will not be matched.

eg

Thanks very much!

Upvotes: 1

Views: 10019

Answers (3)

SvenS
SvenS

Reputation: 795

If the number of exclusions is low, you can use multiple negative look-behinds like this:

(?<!\/foo)(?<!\/bar)(?<!www\.site\.com\/foobar)\.(gif|jpg|png)$

The '/' before foo and bar makes sure the full name matches foo or bar, it doesn't only end in it. If it is possible that there is no '/' before the filename, you need to adjust this part.

One drawback of look-behinds is that you can only use a defined length, so no *, + or {1,5}is allowed. You have to specify every exception by itself.

Note that look-arounds don't change the 'position' in the string from which it is looked at, which is why you can concatenate them like that.

Upvotes: 2

Mark Roberts
Mark Roberts

Reputation: 460

I've found that trying to read my code 6 weeks later means it's almost always better to apply filters like that separately from the regular expression. If you'll pardon a little perl:

# Apply original png/gif/jpg filter to get list of files
my @files = qw/
    asdf.jpg
    bar.png
    fdsa.png
    foo.gif
    foo.jpg
/;

# Filter files to only those that don't look like ^<forbidden>\.
@files = grep {
    $_ !~ /^(foo|bar)\./
} @files;

This is notably also how people tend to string shell commands together.

Upvotes: 1

codaddict
codaddict

Reputation: 454920

You can use:

^(?!(foo|bar)\.(gif|jpg|png)$).*\.(gif|jpg|png)$

See it

Upvotes: 2

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