Hi, this is not a job for a regexp. Use the core module File::Basename to handle stripping extensions, or even better use Path::Tiny or Path::Iterator::Rule to find the files and get your desired output.

Here's one way:

$ ls /tmp/11106920/
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123456.tif    123_456.tif    666_666.jpeg    678_910.tif
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$ perl -Mstrict -MPath::Tiny -wE 'path("/tmp/11106920")->visit( sub { 
+say $_->basename(".tif") if /[0-9]+_[0-9]+\.tif/ } );'
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678_910
123_456
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Hope this helps!