perl print question

hoffa4444 · #1 (**permalink**) 01-24-06, 18:40

Hello,

I have numerous files with tons of information in them. Everything stays the same (format wise) each time the file is created. What I want to do is search for a specific word(s) and print the line directly above it into another file. The word(s) I'll be searching for will remain the same every time. The file will look something like this:

my name is earl (guy)
say: hello
good: bye
etc
no

my name is frank (crazy)
say: goodbye
hello:
etc
yes

What I want to do is print the first line above every section that has "say: hello" on one line into another file. And get rid of the (* after the line im printing. I don't have any issues finding the "say: hello". I'm having trouble printing the line above "say: hello". Anyone have any ideas as to how I can about printing the line above the keywords i'm looking for?

Thanks in advance,

-Hoffa

hyperbole · #2 (**permalink**) 01-25-06, 12:00

Try something like:

Code:

   open(INPUT, "< file");

   $prev_line = "";
   while ($line = <INPUT>)
     {
      if  (    ($line =~ m/^say hello:/)
           and (length($prev_list) > 0)
          )
        { print "$prev_line\n"; }

      $prev_list = $line;
     }

.

Pat Phelan · #3 (**permalink**) 01-25-06, 13:33

Working along the same lines, but in what I consider more "Perl-ish" fashion I'd suggest:

Code:

#  ptp  20060125  Show the line before a line that matches a pattern

$p = <>;

while (<>) {
   if (/^say: hello$/) { print $p };
   $p = $_;
   };

This eliminates the need to have a corporeal file (it will just as happily read a stream or work within a pipe), it only uses one variable, and makes better use of built in Perl features... It also produces the correct output against the test case presented.

-PatP

senza_nome · #4 (**permalink**) 01-26-06, 22:02

along Pat's lines: using ping-pong buffers

note: $i=1-$i oscillates between 0 and 1 if we begin with $i = 0 or $i = 1;
note: if $a[$i] is the hello line, $a[1-$i] is the previous line.

Code:

my($i,@a)=0;
while ($a[$i=1-$i]=<>) {
   print $a[1-$i] if (a[$i] =~ /^say: hello$/);
    };

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