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Re: [Solved]Need to extract a particular block of lines between two patterns

by runrig (Abbot)
on Nov 09, 2017 at 21:50 UTC ( #1203084=note: print w/replies, xml ) Need Help??


in reply to [Solved]Need to extract a particular block of lines between two patterns

Use the return value of the flip-flop:
my $count; while (<$fh_r>) { if (my $status = /START/ .. /END/) { $count++ if $status == 1; print if $count == 2; } }
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Re^2: [Solved]Need to extract a particular block of lines between two patterns
by chengchl (Novice) on Nov 11, 2017 at 01:33 UTC

    Hi Runrig,

    Thank you so much for the clear explanation! It works perfect on my side. Out of curiosity, I also modified the code to print out the $status each line of the matched patterns - print "$status\t$count\t$_" if $count == 2; And I got the output results as:

    1 2 START 2 2 lines to be extracted 3E0 2 END

    Do you by any chance know why the third line is 3E0 and what does that stand for? Thank you in advance!

      ... why the third line is 3E0 and what does that stand for?

      From the discussion of Range Operators in scalar context (the "flip-flop" operator):

      The right operand is not evaluated while the operator is in the "false" state, and the left operand is not evaluated while the operator is in the "true" state. ... The value returned is either the empty string for false, or a sequence number (beginning with 1) for true. The sequence number is reset for each range encountered. The final sequence number in a range has the string "E0" appended to it, which doesn't affect its numeric value, but gives you something to search for if you want to exclude the endpoint.
      [Emphases added]
      So IOW, the final sequence number matches  qr{ \A \d+ E0 \z }xms See also The Scalar Range Operator ("Exluding Markers" section) and Flipin good, or a total flop? (specifically Re: Flipin good, or a total flop?), both in the Monastery's Tutorials section.


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