unfolding a file on linux

I have a huge textfile, approx 400.000 lines 80 charachters wide on liux.

Need to "unfold" the file, merging four lines into one ending up having 1/4 of the lines, each line 80*4 charachters long.

any suggestions?

From stackoverflow

• perl -pe 'chomp if (++$i % 4);'
  

  Lars Wirzenius : This is beautifully short. It seems to lack the final newline in the output, though.

  kmkaplan : That must be because the number of lines in your file is not a multiple of four.

• I hope I understood your question correctly. You have an input line like this (except your lines are longer):

  abcdef
  ghijkl
  mnopqr
  stuvwx
  yz0123
  456789
  ABCDEF
  

  You want output like this:

  abcdefghijklmnopqrstuvwx
  yz0123456789ABCDEF
  

  The following awk program should do it:

  { line = line $0 }
  (NR % 4) == 0 { print line; line = "" }
  END { if (line != "") print line }
  

  Run it like this:

  awk -f merge.awk data.txt
  

• An easier way to do it with awk would be:

  awk '{ printf $0 } (NR % 4 == 0) { print }' filename
  

  Although if you wanted to protect against ending up without a trailing newline it gets a little more complicated:

  awk '{ printf $0 } (NR % 4 == 0) { print } END { if (NR % 4 != 0) print }' filename
  

  dmckee : Cute, though I suspect shares the "sometime lacks a trailing newline" problem with the perl solution suggested by kmkaplan. None-the-less, props for clarity and terseness.

  David Dean : I've added a more complicated example that fixes that problem. Still relatively simple.