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Re: Printing line before matching expression

by johngg (Abbot)
on Sep 10, 2013 at 23:52 UTC ( #1053383=note: print w/ replies, xml ) Need Help??

in reply to Printing line before matching expression

You have to keep a buffer of previously read lines large enough to retain the nth previous line you are wanting to print. How to handle the situation where there aren't n lines before your found line is an exercise left to the reader.

$ perl -Mstrict -Mwarnings -E ' open my $inFH, q{<}, \ <<EOD or die $!; line 1 line 2 line 3 line 4 line 5 line 6 line 7 line 8 line 9 EOD my $lineBeforeMatch = 5; my @prevLines; my $lookFor = qr{line 7}; while ( <$inFH> ) { push @prevLines, $_; shift @prevLines if $#prevLines > $lineBeforeMatch; print $prevLines[ 0 ] if m{$lookFor}; }' line 2 $

I hope this is helpful.



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