http://www.perlmonks.org?node_id=731489


in reply to Using grep to pick out lines in a text file

This could be a useful if you are wondering the solution with minimal number of lines. 
open( INPUTFILE, "<WordNet.txt" ) or die "$!";

open( OUTPUTFILE, ">>WordNetTest2.txt" ) or die "$!";

grep {  /adj:/ and print OUTPUTFILE $prev,$_;$prev=$_  } (<INPUTFILE>)
+;

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In Section Seekers of Perl Wisdom