$folder2 = "C:/neaq/ArcData/bluefin/data_dens/1994sptr/";
$textfile2 = "10.06.94.txt";
open(INFILE2, "$folder2$textfile2") or 
        die "Cannot open: $textfile2\n";
[download]

open FH, "first file" || die "problem with first file : $!";
@first =<FH>; # slurp into array
close FH;
open FH, "next file" || die "problem with first file : $!";
@second =<FH>; # slurp into array
close FH;
# at this point, we've got the lines of each file in two different arr
+ays.
# if it's important that they have the same number of lines, you can 
# check with if (scalar (@first) != scalar (@second)) {...
# 
    
# now start output to the third file. maybe check to see if it exists?
open OUTPUT, ">output.txt";
# since we're reading from 2 different arrays
# it's easier to use for (0..$#first) rather than foreach (@first)
# so that we can apply the element number to both arrays.
# 
my $sep=","; # specifies comma separated output. this might be bad if 
+your data has commas in it.
 
for (0..$#first) { # this is a liability if the second file has more l
+ines...    
    print OUTPUT join $sep, split (/\s+?/, $first($_)), split (/\s+?/,
+ $second($_));   
}
close OUTPUT;
[download]

my $folder1 = 'folder1'
my $folder2 = 'folder2';
my $folder_out = 'outfolder';
my $textfile = 'file.txt';

open(my $file1,   "< $folder1/$textfile")    or die $!;
open(my $file2,   "< $folder2/$textfile")    or die $!;
open(my $outfile, "> $folder_out/$textfile") or die $!;

while (my $line1 = <$file1> ) {
   my $line2 = <$file2>;

   my @data1 = split, $line1;
   my @data2 = split, $line2;

   print $outfile @data1[1..7], $data2[3], "\n";
}
close($file1);
close($file2);
close($outfile);
[download]

-- Hofmator

I see a couple of problems: first, and I'm sure you're about to hear a lot of this: You should always  use strict; and use warnings;. Strict forces you to localize your variables with my, both directives (placed at the top of your program) are very useful for helping you debug your program).

As for the immediate problems: While reading data in I notice that you have this (similar for the second one):

@data = split;
($mask,$x,$y,$ftdens) = @data;
[download]

Finally your output is the biggest problem. Your program is hanging because you've opened the output file and then did:

while(<>) {
[download]

Here is a program that works on comma separated values. You'll have to taylor it for your own data structure :)

#!/usr/bin/perl
use strict;
use warnings;

my $file1 = "file1.txt";
my $file2 = "file2.txt";
my $outfile = "outfile.txt";

my @data1 = ();
my @data2 = ();
open(INFILE1,"$file1") or die "Couldn't open $file1: $!\n";
while(<INFILE1>) {
    chomp;
    my @line = split(/,/,$_);
    push(@data1,\@line);
}
close(INFILE1);

open(INFILE2,"$file2") or die "Couldn't open $file2: $!\n";
while(<INFILE2>) {
    chomp;
    my @line = split(/,/,$_);
    push(@data2,\@line);
}
close(INFILE2);

# now merge the data in the outfile
open(OUTFILE,">$outfile") or die "Couldn't open $outfile: $!\n";
my $count = 0;
foreach(@data1) {
    print OUTFILE @$_,$data2[$count]->[3];
    $count++;
}
close(OUTFILE);
[download]

I hope that helps. Post some of your data maybe we can help further

Chris

Update: Opps Fletch is correct split $_ splits on whitespace.

split with no arguments splits on nothing for $_.

Actually it splits $_ on whitespace. See perldoc -f split.</pedant>

Thanks for the tips. I posted a snippet of data in one of the replies below. Let me know if it helps.

#!/usr/bin/perl
$base1   = "C:/neaq/ArcData/bluefin/data_analysis/1994sptr/data";
$base2   = "C:/neaq/ArcData/bluefin/data_dens/1994sptr";
$outfile = "C:/some/dir/to/reports";

opendir(BASE1, "$base1") || die "Cant open $base1\nReason: $!\n";

foreach $file ( grep(/\.txt$/, readdir(BASE1)) ) {
   warn "Skip: No matching $file in $base2\n" 
      && next unless (-f "$base2/$file");

   open(IN, "$base1/$file") 
      || die "Cant access $file\nReason: $!\n";

    while ( <IN> ) {
      @data1 = ( split(/\s+/) )[1,2,3,4,5,6,7];
    }
   close(IN);

   open(IN, "$base2/$file") 
      || die "Cant access $base2/$file\nReason: $!\n";

   while ( <IN> ) {
      $data2 = ( split(/\s+/) )[3];
   }
   close(IN);

   open(OUT, ">>$outfile") 
      || die "Cant append to $outfile\nReason: $!\n";
   print OUT "@data1 $data2\n";
   close(OUT);

} # END foreach $file readdir(BASE1)
#
# or alternately to save up our data and only print once
# push(@out, join(' ', "$file: ", @data1, $data2));
# then loop through out once and print it out here instead
#
[download]

Well actually no. My data files have more than one line. Guess I'm getting many things wrong. The data look like: oldfile:

mask    x    y    dln9476326lce    dln94930101lc
0    8852.68825    442495.5253    82293.02    0
0    9913.98125    442495.5253    82751.22    0
0    10975.27425    442495.5253    83238.23    0
0    10975.27425    441434.2323    81704.7    0
0    12036.56725    440372.9393    80174.36    0
0    12036.56725    439311.6463    80174.36    0
0    12036.56725    438250.3533    78647.4    0
0    13097.86025    438250.3533    79192.59    0
0    13097.86025    437189.0603    77679.91    0
0    13097.86025    436127.7673    77679.91    0
<snip>

I haven't included all the columns, but there are 5 more.
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newfile:

mask    x    y    dln9476331lc
0    23710.79025    396859.92632    0
0    27955.96225    396859.92632    0.2530461
0    29017.25525    395798.63332    0.4151559
0    29017.25525    394737.34032    2.826168
0    19465.61825    393676.04732    0
<snip>
[download]

The files always have the same name in each directory, the same number of lines, and the same structure (within each directory, but different across directories). They are output from a GIS sampling program. The only difference is the days on which they were sampled. Files look like:

C:\neaq\ArcData\bluefin\data_dens\1994_sptr>dir

10.06.94.txt
10.07.94.txt
7.10.94.txt
7.11.94.txt
7.12.94.txt
7.14.94.txt
<snip>

C:\neaq\ArcData\bluefin\data_analysis\1994sptr\data>dir
10.06.94.txt
10.07.94.txt
7.10.94.txt
7.11.94.txt
7.12.94.txt
7.14.94.txt
<snip>
[download]

#my list of files
@ARGV=qw/txt1.txt foo.txt baz.txt etc.foo/;
open OUT,'out.txt';
while(<>){print OUT $_;}
[download]

while (<>) {

It's not hanging, it's waiting for input on STDIN just like you asked it to do. Perhaps you mean to iterate over @data instead?

Look at File::Find for iterating over files.

cut - remove sections from each line of files
paste - merge lines of files

Or perhaps you can use perl for part of it and just merge the results with paste.