topic Re: head / tail function in Operating System - Linux

head / tail function

u856100 — Fri, 04 Apr 2003 11:18:08 GMT

people,

if I have a file thus :

1
2
3
4
5

and I wanted to get a section, or number of lines from the middle (using two line numbers) i.e. :

2
3
4

how would I do this (could I use head or tail?)

many thanks
John

Re: head / tail function

Ramkumar Devanathan — Fri, 04 Apr 2003 11:37:42 GMT

suppose the numbers are as follows in a.txt -

1
2
3
4
5
.
.
.
10

#!/bin/bash

# expects number of lines to be removed from head and tail as argument

nlines=`wc -l a.txt | awk '{print $1}'`

nlines=`expr $nlines - $1`
hlines=`expr $nlines - $1`

tail -$nlines a.txt | head -$hlines

# EOF

should work.

- ramd.

Re: head / tail function

John Poff — Fri, 04 Apr 2003 11:43:10 GMT

Hi,

This is one way to do it using head and tail:

head -4 file | tail +2

The problem with head and tail is that they have a limited buffer space to work with, so they work fine with smaller files but not with large files. Probably Perl is a better choice to work with most any size file. You can do it like this with Perl:

perl -ne '2..4 and print' file

JP

Re: head / tail function

Ramkumar Devanathan — Fri, 04 Apr 2003 12:05:11 GMT

Sorry I misunderstood as a script to remove n lines from beginning and end of file.

Probably perl would be a better option as pointed out.

- ramd.

Re: head / tail function

Goran Koruga — Fri, 04 Apr 2003 12:16:28 GMT

Or even sed :

sed -ne '2,5p' filename

HTH,
G.