Your example suggests that the entire search is to be performed on data appearing once in a single line.

This is due to missing <code> tags. As evidenced by the HTML source code, the OP is as follows: 

Hi,

I would like to know how to grep the first occurrence of a string above(upwards) a reference string.

for (e.x.)in the below set, I would like to get the first occurrence of "AAA" above "XXX".

AAA
BBB
AAA
CCC
XXX

Thanks,
Venkat

To the OP - if you rephrase your problem, you have the solution almost there:

I want to keep track of a pattern I seek for, and output the found string after finding a reference string

which is what ww did for you above already. Hence a possible solution is

#!/usr/bin/perl
# file grep.pl

my $sought    = shift; # from @ARGV
my $reference = shift;
$sought && $reference or die "usage: $0 soughtstring refstring files\n
+";

my $found;
while(<>) {
    chop; # strip newline

    /$sought/ and $found = $_;

    # or, if you want the very first occurence, don't
    # overwrite the variable (see perlop for '||='):
    # /$sought/ and $found ||= $_;

    if (/$reference/) {
        print "$ARGV: '$found'\n" if $found;
        $found = '';
    }
}

[download]

to be used as

$ perl grep.pl AAA XXX example.txt

[download]

which invoked upon this example.text

  1 YYY
  2 first AAA
  3 BBB
  4 CCC
  5 second AAA
  6 freida
  7 XXX
  8 GGG
  9 FFF
 10 third AAA
 11 XXX
 12 ozymandis
 13 BBB
 14 blorflydick
 15 XXX
 16 fourth AAA

[download]

produces this: 

example.txt: '  5 second AAA'
example.txt: ' 10 third AAA'

[download]

Lines 2 and 16 are not printed. If you use the commented alternative, line 2 is printed instead of line 5.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re^2: Grep the first occurrence of a string above a reference string by shmem
in thread Grep the first occurrence of a string above a reference string by venkat1312

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