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

Hello Oh Masters of Perl Wisdom, I need a script that reads in a text file, replaces the first line and outputs another file with the new first line along with the rest of the file. In the first line I need to write out a a 6 character string that is always on the 12th line of the file at the 50th position. Here is the code I have that does everything but get that 6 character variable. I wrote some other code to get the variable, but I can't seem to get the script to loop back to the top to start writing out the whole file. I want the 6 character variable to go where the 'JF' literal goes on the $newjob line in this code... 
 
{
    $buffer = '';
    $filename = '';
    $line = '';
    $job = '';
    $temp = '';
    $index_job = 0;
    $key = '';
    $tray = '';

    print LOG "$mday$mon$year $hour:$min:$sec  Processing Data file, s
+plitting Jobs.\n";    
    # Skip first line.
    #<INFILE>;
    while (<INFILE>) {
        $line = $_;
        if ($line =~ /^(\^JOB.*)\n$/i) #if the current line is a ^job 
+line then
        {
            $tmp = $1; #Set $tmp equal to what is in (\^JOB.*) ie: ^jo
+b PATIENTLBL -c1 -zDP7P
            @pieces = split(/ /, $tmp); #Split-up the entire line, on 
+spaces, into @pieces
            $newjob = $pieces[0]." "."JF".$pieces[1]." ".$pieces[2]." 
+".$pieces[3]."\n"; #Rebuild ^job line with JF in front of jobname
            #print "newjob :    ".$newjob;
            $temp = $newjob; #Assign new ^job line to $temp to create 
+new file(s)
            if ($buffer ne "") #Not first job
            {
                print LOG "$mday$mon$year $hour:$min:$sec  Found:  $jo
+b";    
                $buffer_job[$index_job++] = $buffer;
            }
            $job = $temp;
            $buffer = $temp;
        }else{
            $buffer .= $line;
        }
        
    }

[download]

Replies are listed 'Best First'.
Re: Text Processing
by arturo (Vicar) on Apr 21, 2001 at 00:48 UTC

    The biggest piece of the puzzle you need is the seek function (perldoc -f seek on your system or perlfunc:seek for a quick ref). While you can open files for both read and write access, I like to work with a scratch file. So here are the steps the way I'd do it: 

    open OLDFILE, $oldfilename 
 or die "Can't open $oldfilename: $!\n";
# get length of first line
my $start_pos = length(<OLDFILE>);

# now read in next 11 lines
for (1..11) {
 $_ = <OLDFILE>;
}
# we've got the 12th line in $_
# nab the 6 chars starting at the 50th position of $_
my $field = substr($_, 49,6);
#rewind to the beginning of the second line
seek(OLDFILE, $start_pos,0);

open NEWFILE, "> $oldfilename.new" 
 or die "Can't open $oldfilename.new for write: $!\n";
print NEWFILE "STring with $field in it\n";
# now write eatch line of OLDFILE INTO NEWFILE
print NEWFILE while (<OLDFILE>);
close OLDFILE;
close NEWFILE;
rename ($oldfilename, "$oldfilename.bak") 
 or die "Can't move $oldfilename: $!\n";
rename ("$oldfilname.new", $oldfilenme)
 or die "Can't create new $oldfilename: $!\n";

    [download]

    Yeuch that's kinda clunky, but those are the steps.

    HTH

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Re: Text Processing
by Sprad (Hermit) on Apr 21, 2001 at 00:45 UTC
    I just recently discovered some functions that are good for this sort of thing. seek() and tell(). tell(FILE) will return your current position in the file FILE, and seek(FILE, $n, 0) will send you to the location in FILE stored in $n. Use them like this: 
    # open your file
$top_of_file = tell(FILE);
# go fetch your variable
seek(FILE, $top_of_file, 0);
# now you're back at the top

    [download]
    They're handy in other situations, too. You can tell() any number of positions in the file, and go back to them at will. I bet there's a JAPH in that concept somewhere...

    ---
    I'm too sexy for my .sig.

[reply]
[d/l]

      Silly ol' me forgot about tell in my response (I used that inelegant length thing). Oh well; I just wanted to register the caveat that you must read in the first line *before* you do the call to tell, otherwise you get the uninformative result 0.

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        But isn't that the very beginning of the file? Or is that not where we want to be?

        ---
        I'm too sexy for my .sig.

[reply]
Re: Text Processing
by Sifmole (Chaplain) on Apr 21, 2001 at 00:36 UTC 
    @pieces = split(/ /, $tmp); #Split-up the entire line...
$newjob = $pieces[0]." "."JF".$pieces[1]." ".$pieces[2].
          " ".$pieces[3]."\n";
$temp   = $newjob;

    [download]
    Could probably be replaced with... 
    $tmp =~ s/^([^ ]+\s+)/$1JF/;

    [download]
[reply]
[d/l]
[select]
      I need JF to be replaced by a string from the 12th line...
[reply]
        Well you can still use the expression... Just replace the JF with a var that contains the string you want to put in there. I thought you already had the code to extract the string. Sorry.
[reply]
Re: Text Processing
by greenFox (Vicar) on Apr 21, 2001 at 02:13 UTC
    Here is another approach not using seek. (Untested) 
    open (INFILE, $infile) || die "but... $!";
open (OUTFILE, ">$outfile") || die "but... $!";

my @hold;
while(<INFILE>){
    if ($. < 12){
        push @hold, $_;
        next;
    }
    if ($. == 12){
        # grab some data from the 12th line
        # perform some funky manipulation on it
        print OUTFILE "new funky data from 12th line";
        print OUTFILE @hold;
        next;
    }
    print OUTFILE $_;
}

    [download]

    see perlman:perlvar

    TIMTOWTDI :)

    --
    my $chainsaw = 'Perl';

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[d/l]
Re: Text Processing
by Ixandantilus (Initiate) on Apr 21, 2001 at 06:48 UTC
    Thanks to you all!
[reply]

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