Stupid "cat" tricks that work.
by Mike Chirico
The "cat" command is very powerful and fast.  These may be some tips
you haven't seen before, such as "summing" each row of numbers, converting
a random number of columns to a specific number N,  or getting
the contents of multiple files from one list.
These tips are simple,  fast and worth a quick look.
TIP 43:
     "cat" the Contents of Files Listed in a File, in That Order.

       SETUP (Assume you have the following)

              $ cat file_of_files

                  $ cat file1
          This is the data in file1

            $ cat file 2
          This is the data in file2

       So there are 3 files here "file_of_files" which contains the name of
       other files.  In this case "file1" and "file2". And the contents of
       "file1" and "file2" is shown above.

               $ cat file_of_files|xargs cat
    This is the data in  file1
    This is the data in  file2

TIP 44:

     Columns and Rows -- getting anything you want.

     Assume you have the following file.

        $ cat data
           1  2    3       
   4 5         
   6 7 8 9 10  
   11 12       
   13 14       

     How to you get everything in  2 columns?

        $ cat data|tr ' ' '\n'|xargs -l2
   1 2 
   3 4 
   5 6 
   7 8 
   9 10
   11 12
   13 14

    Three columns?

        $ cat data|tr ' ' '\n'|xargs -l3
   1 2 3  
   4 5 6  
   7 8 9  
   10 11 12
   13 14  

    What's the row sum of the "three columns?"

        $ cat data|tr ' ' '\n'|xargs -l3|tr ' ' '+'|bc      
  Note, thanks to, Steven Heiner (  The above can be
       $ tr ' ' '\n' < data|xargs -l3|tr ' ' '+'|bc
TIP 62:

     If you have multiple blank lines, squeeze these lines down to one,
     then, try the following:

          $ cat -s <file>

     Want to number the lines?

          $ cat -n <file>

     Want to see all the ctl characters?
     See the following program:
      Which is used to generate "mout" used below

 $ cat -v mout|tail
         test M-v  
test M-w  
test M-x  
test M-y  
test M-z  
test M-{  
test M-|  
test M-}  
test M-~  
test M-^? 
NOTE!  The Useless Use of Cat Award   NOTE THE FOLLOWING:

In nearly all cases  
       $  cat file | some_command and its args ...

can be rewritten as:

    $  <file some_command and its args ...

        $ cat data|tr ' ' '\n'|xargs -l2
Can be rewritten as:
        $ tr ' ' '\n' < data |xargs -l2

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Chirico img Mike Chirico, a father of triplets (all girls) lives outside of Philadelphia, PA, USA. He has worked with Linux since 1996, has a Masters in Computer Science and Mathematics from Villanova University, and has worked in computer-related jobs from Wall Street to the University of Pennsylvania. His hero is Paul Erdos, a brilliant number theorist who was known for his open collaboration with others.

Mike's notes page is souptonuts. For open source consulting needs, please send an email to All consulting work must include a donation to Logo Logo