Issue with Unix cat command


 
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# 1  
Old 10-29-2007
Java Issue with Unix cat command

Hi Experts,

I am finding the performance of cat command is very wierd, it is taking more time to merge the files into a single file. We have a situation where we would be merging more than 100 files into a single file, but with cat command it is running slow. I tried doing with paste, join and cat, but cat is working faster than any of these. Please guide me if any one has faced similar issue, please help. How about sed and awk commands usage for merging bigger files.

Thanks,
Rajiv
# 2  
Old 10-29-2007
your statements are contradicting each other.

Could you please clarify that ? Smilie

Quote:
it is taking more time to merge the files into a single file.
Quote:
but with cat command it is running slow.
Quote:
I tried doing with paste, join and cat, but cat is working faster than any of these.
# 3  
Old 10-29-2007
Java Issue with Unix cat command

Matrixmadan,

We are currently using cat command to combine files, basically appending files together into a single file.

cat file1 file2 file3 .....file 100 > final_file

I tried creating a file list and ran cat command this way....

cat filelist | xargs cat >> final_file

There is no performance gain. The file1, file2 ...file 100 are of varying size, and the final_file is very big, somewhere around 15 GB. I wanted to know is there a better way to combine multiple files into one.

Thanks,
Rajiv
# 4  
Old 10-29-2007
Code:
#! /opt/third-party/bin/perl

use strict;

my @contents;
my @files_arr;

my $DIR1 = "/source/directory/";
my $big = "thebigfile.txt";

opendir(DIR, $DIR1) || die "Unable to open files in Dir : $DIR1 <$!> \n";
  @files_arr = readdir(DIR);
closedir(DIR);

open(BIG, ">", $big) or die "Unable to open file $big <$!> \n";

foreach (@files_arr) {
  if( ! /^\./ && ! /^\.\./ ) {
    print "$_\n";
    $_ = $DIR1 . $_;
    open(FILE, "<", $_) or die "Unable to open file $_ <$!> \n";
      @contents = <FILE>;
    close(FILE);
    print BIG "@contents";
  }
}

close(BIG);

exit 0

# 5  
Old 10-29-2007
Issue running cat command

MatrixMadan,

I tried running your script, but perl component is not available. I am getting error as "Perl not installed".

Thanks,
Rajiv
# 6  
Old 10-29-2007
cat is pretty efficient.

The operation is going to take a combination of CPU and IO. With the volumes you are talking about the IO will have more overhead that the CPU component.
# 7  
Old 10-29-2007
Java Issue with cat command

Porter,

I do agree with you. But still how far can we tune to speed up the process. Becuase of this file appending, whole load time is impacted. Let me know if you have any other thoughts on this...

Thanks,
Rajiv
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