Reports

Ahoy!

Here is a solution in Perl. Because the lines are before the match, you will have to use a buffer. I included a $bufferSize command line argument. An array named @buffer will always have the last $bufferSize lines. When you find a match, print the buffer which contains the matching line at the end. Here is the code. I ran this on a text file of Programming Perl by Larry Wall.

#!/usr/bin/perl -w

=begin
#usage perl thisFile.pl bufferSize inputFile

#print n lines before match.  Because it is BEFORE the match, you will 
need to use a buffer.  I have limited the buffer to just the given 
bufferSize, but you could store the entire file in a buffer if need be.

=end

=cut

my $bufferSize = shift;                           #grab buffer size from command line arguments
my @buffer;

while(<>){
  push(@buffer, "$_");                            #store current line in buffer to be accessed when a match is found
  if($#buffer > $bufferSize){ shift(@buffer); }   #if the buffer is bigger than $bufferSize, remove a line from the beginning of the array with shift, pop removes from the end of the array
  if(/diamond/i){                                  #match found, print buffer
    print "\n\n***Match Found: Line $.***\n";
    my $i=1;
    for(@buffer){print "$i\t: $_"; $i++;}
  }
}

Output looks like this

$ perl print.n.lines.before.match.pl 15 programming.perl.txt 


***Match Found: Line 25975***
1   : stalled on the target system. (It might need some shared libraries, though, if you
2   : didn’t link everything statically.) However, this program isn’t really any different
3   : than the regular Perl interpreter that runs your script. It’s just precompiled into
4   : a standalone executable image.
5   : The B::CC module, however, tries to do more than that. The beginning of the C
6   : source file it generates looks pretty much like what B::C produced5 but, eventu-
7   : ally, any similarity ends. In the B::C code, you have a big opcode table in C that’s
8   : manipulated just as the interpreter would do on its own, whereas the C code
9   : generated by B::CC is laid out in the order corresponding to the runtime flow of
10  : your program. It even has a C function corresponding to each function in your
11  : program. Some amount of optimization based on variable types is done; a few
12  : benchmarks can run twice as fast as in the standard interpreter. This is the most
13  : ambitious of the current code generators, the one that holds the greatest promise
14  : for the future. By no coincidence, it is also the least stable of the three.
15  : Computer science students looking for graduate thesis projects need look no fur-
16  : ther. There are plenty of diamonds in the rough waiting to be polished off here.

Here is a solution to find n lines AFTER a match from a similar question here.

print specific number of lines after matching pattern

Its almost exactly the same but doesnt require a buffer since the lines are AFTER the match.

#!/usr/bin/perl -w

#usage perl thisFile.pl bufferSize inputFile

#print n lines after match
$n = shift;
while(<>){
  if( /diamond/i ){
    print "\n\n***Match found: Line $.***\n$_"; #print header and  matching line
    #print next 81 lines
    for( 1 .. $n ){
      print "$_:\t" . <>;
    }
  }
}

Output looks like this

$ perl print.n.lines.after.match.pl 15 programming.perl.txt 


***Match found: Line 25975***
0:  ther. There are plenty of diamonds in the rough waiting to be polished off here.
1:  
2:  
3:  Code Development Tools
4:  The O module has many interesting Modi Operandi beyond feeding the exasper-
5:  atingly experimental code generators. By providing relatively painless access to
6:  the Perl compiler’s output, this module makes it easy to build other tools that
7:  need to know everything about a Perl program.
8:  The B::Lint module is named after lint(1), the C program verifier. It inspects
9:  programs for questionable constructs that often trip up beginners but don’t nor-
10: mally trigger warnings. Call the module directly:
11:     % perl –MO=Lint,all myprog
12: 
13: 
14: 
15:

Good Luck!

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