Is it possible to sort a huge text file using Linux sort command by a number at the end of each line?

Question

I am trying to sort a text file where the lines are in the following format:

! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 6

and want to sort numerically descending by the number at the end (i.e 6 in this example). The lines do not have a predicable number of columns using space as a delimiter, but using ||| as a delimiter there are always 5 columns, and the final column always has 3 space delimited numbers, the last of which to sort by. The text file is around 15gb and I did have a perl script I wrote to do it but it only worked on my old laptop which had 32gb of RAM because perl loads the whole file at once. Now I am stuck with 8gb RAM and it just churns the swap file for days. I have heard that the standard linux sort command handles huge files more gracefully but I can't find a way to make it use the number at the end.

Answer 1

Maybe it is a bit tricky, but this mix of commands can make it:

awk '$1=$NF" "$1' file | sort -n | cut -d' ' -f2-

The main idea is that we print the file appending the last value in the front of the line, then we sort and we finally remove that value from the output.

• awk '$1=$NF" "$1' file As the parameter you want to sort by is the last one in the file, let's print it also in the first field.
• sort -n Then we pipe to sort -n, which sorts numerically.
• cut -d' ' -f2- and we finally print out the value we temporally used.

Test

$ cat a
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 6
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 79
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 19
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 8
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 89
$ awk '$1=$NF" "$1' a | sort -n | cut -d' ' -f2-
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 6
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 8
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 19
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 79
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 89

Showing each step:

$ awk '$1=$NF" "$1' a 
6 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 6
79 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 79
19 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 19
8 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 8
89 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 89
$ awk '$1=$NF" "$1' a | sort -n
6 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 6
8 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 8
19 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 19
79 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 79
89 ! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 89
$ awk '$1=$NF" "$1' a | sort -n | cut -d' ' -f2-
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 6
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 8
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 19
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 79
! ! ! ! ! ||| ! ||| 1.25846e-05 0.248369 3.02708e-07 0.662955 2.718 ||| 0-0 1-0 2-0 3-0 4-0 ||| 476773 1.98211e+07 89