splatohara has asked for the wisdom of the Perl Monks concerning the following question:

I have a script which is reading from a file and i am assigning a variable a value from an element in an array produced during script. I want a section of the script to run only if that value of that element of the array changes , if it does not not i want it to return to the start 
while ($line=<In>) {

@temp = split(/[=]/,$line);

if ($temp[1] >100)
        {
        print "Session id: $temp[1]  ";
        $sessid = $temp[1];

       }

#I want the following to run only if  $sessid changes

      $modtyp = $temp[1];

if($modtyp == 20)
{
print " V34\n\n ";
}

elsif ($modtyp == 9)
        {
print " no connection\n\n";
}

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Re: runnig part of script when variable changes
by vek (Prior) on Feb 21, 2002 at 13:49 UTC
    First of all, use strict and -w or warnings.

    Now to the problem at hand. You don't give many specifics so the following code just checks to see if the value of $temp[1] changes from line to line in your file: 
    my $firstLineFlag++;
my $sessid;
while (my $line = <IN>) {
   my @temp = split (/[=]/, $line);
   if ($temp[1] > 100) {
      print "Session id: $temp[1]  ";
   }

   if ($firstLineFlag) {
      $sessid = $temp[1];
      $firstLineFlag = '';
   }
   if ($temp[1] ne $sessid) {
      if ($temp[1] == 20) {
         print " V34\n\n ";
      } elsif ($temp[1] == 9) {
         print " no connection\n\n";
      }
      $sessid = $temp[1];
   }
}

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[reply]
[d/l]
[select]
      I am getting the error " can't increment in my at var.pl line x, near "++;"
[reply]
        Really? Please post your code. I'm assuming the offending line is the my $firstLineFlag++; line which (if used as I posted) will just set the value of $firstLineFlag to 1.
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[d/l]
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Re: runnig part of script when variable changes
by splatohara (Novice) on Feb 21, 2002 at 17:33 UTC
    here is the code 
    #!/perl/bin

open (In,"tascomod.log") or die ("an not open file at the moment");
open (Out, "tasmodtypfinrpt.txt") or die ("cannot open output file may
+be you sho
uld create one");

print "\n\n Session id    Modulation \n\n";

my $firstlineFlag++;
my $sessid;
while (my $line = <IN>) {
   my @temp = split (/[=]/, $line);
   if ($temp[1] > 100) {
      print "Session id: $temp[1]  ";
   }

   if ($firstLineFlag) {
      $sessid = $temp[1];
      $firstLineFlag = '';
   }
   if ($temp[1] ne $sessid) {
      if ($temp[1] == 20) {
         print " V34\n\n "; 

}
$sessid = $temp[1];
}
}

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[reply]
[d/l]
      If you'd had 'use strict' at the top of the script you'd have spotted that '$firstlineFlag' is not the same as '$firstLineFlag'. Also the declaration of '$firstlineFlag' increments an uninitialised variable (which would have been caught with '-w'). Once it runs cleanly with 'strict' and 'warnings', you'll be in a better position to find out what the problem is with your algorithm. (I suspect that it will be OK when '$firstlineFlag' is changed to '$firstLineFlag').

      rdfield

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