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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
RRP £29.95 ($39.95)

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causes Perl to assume the following loop around your program, which makes it iterate over filename arguments somewhat like sed -n or awk:

  while (<>) {
      ...             # your program goes here

Note that the lines are not printed by default. See -p to have lines printed. If a file named by an argument cannot be opened for some reason, Perl warns you about it and moves on to the next file.

Also note that <> passes command line arguments to , which doesn't necessarily interpret them as file names. See 7 for possible security implications.

Here is an efficient way to delete all files that haven't been modified for at least a week:

find . -mtime +7 -print | perl -nle unlink

This is faster than using the -exec switch of find because you don't have to start a process on every filename found. It does suffer from the bug of mishandling newlines in pathnames, which you can fix if you follow the example under -0.

BEGIN and END blocks may be used to capture control before or after the implicit program loop, just as in awk.

ISBN 9781906966027Perl Language Reference ManualSee the print edition