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I have multiple files that contain ascii text information in the first 5-10 lines, followed by well-tabulated matrix information. In a shell script, I want to remove these first few lines of text so that I can use the pure matrix information in another program. How can I use bash shell commands to do this?

If it's any help, I'm using RedHat and an Ubuntu linux systems.

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2 Answers

up vote 6 down vote accepted 
$ cat t.txt
12
34
56
78
90
$ sed -e '1,3d' < t.txt
78
90
$ tail -n +4 t.txt
78
90
$ awk 'NR > 3 { print }' < t.txt
78
90
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You can also use sed in-place without a temp file: sed -i -e 1,3d yourfile. This won't echo anything, it will just modify the file in-place. If you don't need to pipe the result to another command, this is easier. – Yanick Girouard May 2 at 23:46
As long as the file is not a symlink or hardlink. – jw013 May 3 at 0:26
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up vote 2 down vote

If the tabulated lines are the ones that have a tab character:

grep '␉' <input_file >output_file

(␉ being a literal tab character) or equivalently

sed -n '/␉/p' <input_file >output_file

In a bash/ksh/zsh script, you can write $'\t' for a tab, e.g. grep $'\t' or sed -n $'/\t/p'.

If you want to eliminate 10 lines at the beginning of the file:

tail -n +11 <input_file >output_file

(note that it's +11 to eliminate 10 lines, because +11 means “start from line 11” and tail numbers lines from 1) or

sed '1,10d' <input_file >output_file

On Linux, you can take advantage of GNU sed's -i option to modify files in place:

sed -i -n '/\t/p' *.txt

Or you can use a shell loop and temporary files:

for x in *.txt; do
  tail -n +11 <"$x" >"$x.tmp"
  mv "$x.tmp" "$x"
done

Or if you don't want to modify the files in place, but instead give them a different name:

for x in *.txt; do
  tail -n +11 <"$x" >"${x%.txt}.data"
done
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"tabulated" usually means "pretty-printed in a table", not "indented with tab characters". – Ignacio Vazquez-Abrams May 3 at 2:14
@IgnacioVazquez-Abrams I know. The pretty-printed table sometimes uses tab characters, that's easier to spot than aligned columns. Of course, if Paul gave a sample input, I could give a better matcher. – Gilles May 3 at 10:04
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