The -f is a file operator that returns true if the file (by default given in $_) exists so the grep is testing to see if named files exist and dropping any that don't exist out of the list.

grep can use either grep {...} @list or grep ..., @list syntax. You are using the second variant.

grep {-f} map {...} @list;

[download]

might be clearer.

Update: Oh, and to "find all the files" you need something like glob:

my @files = grep {-f} map {glob "$_/*vp.o$id"} qw/ archiv/;

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Although if you are using glob the grep is probably redundant.

Premature optimization is the root of all job security

In reply to Re:Need help understanding code snippet with "grep -f" by GrandFather
in thread Need help understanding code snippet with "grep -f" by fifaltra

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