Beefy Boxes and Bandwidth Generously Provided by pair Networks
Think about Loose Coupling
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

You mention wanting to print the lines above and below a matching line, but your code prints the matching line, too. In case you wanted to print all (two or) three lines, consider the following that you can adapt for files:

use strict; use warnings; my ( $prevLine, $nextLine ); for ( ; ; ) { last if eof DATA; chomp( my $currLine = defined $nextLine ? $nextLine : <DATA> ); if ( $currLine =~ /match this/ ) { print '-' x 25, "\n"; chomp( $nextLine = <DATA> ) if !eof DATA; print $prevLine, "\n" if defined $prevLine; print $currLine, "\n"; print $nextLine, "\n" if defined $nextLine; print '-' x 25, "\n"; } else { undef $nextLine; } $prevLine = $currLine; } __DATA__ The first line match this Not this abcdefg The one above Another match this 1 Another match this 2 the one below match this 2 zxcvbnn Another match this blank above Second to the last line The last line match this

Output:

------------------------- The first line match this Not this ------------------------- ------------------------- The one above Another match this 1 Another match this 2 ------------------------- ------------------------- Another match this 1 Another match this 2 the one below match this 2 ------------------------- ------------------------- Another match this 2 the one below match this 2 zxcvbnn ------------------------- ------------------------- Another match this blank above Second to the last line ------------------------- ------------------------- Second to the last line The last line match this -------------------------

The dashes are printed to show the desired output. If the first or last line is a match, only two lines are printed. If you only want the lines above and below a matching line, delete print $currLine, "\n";.

Hope this helps!

Addition: If you want to avoid printing the same line more than once--like in the example above--and have output that more closely resembles grepping the file, you can do the following:

use strict; use warnings; my ( $prevLine, $nextLine, %printed ); for ( ; ; ) { last if eof DATA; chomp( my $currLine = defined $nextLine ? $nextLine : <DATA> ); if ( $currLine =~ /match this/ ) { chomp( $nextLine = <DATA> ) if !eof DATA; print $prevLine, "\n" if defined $prevLine and !$printed{$prev +Line}++; print $currLine, "\n" if !$printed{$currLine}++; print $nextLine, "\n" if defined $nextLine and !$printed{$next +Line}++; } else { undef $nextLine; } $prevLine = $currLine; } __DATA__ The first line match this Not this abcdefg The one above Another match this 1 Another match this 2 the one below match this 2 zxcvbnn Another match this blank above Second to the last line The last line match this

Output:

The first line match this Not this The one above Another match this 1 Another match this 2 the one below match this 2 zxcvbnn Another match this blank above Second to the last line The last line match this

This uses a hash to keep track of previously printed lines, so they're shown only once.


In reply to Re: How to print the lines immediately above and below a matching line? by Kenosis
in thread How to print the lines immediately above and below a matching line? by Bio90

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others about the Monastery: (6)
    As of 2015-07-05 15:40 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (67 votes), past polls