Printing Nth line from file

[ProgramIt]

Can someone explain how you would go about printing the Nth line from a file. I understand multiple ways of doing it if N is a constant

echo `awk '{ if(NR==5) print $0 }' input`
echo `sed -n '5p' input`
echo `head -n5 input | less -n1`

but how do you do this if N is not a constant. The way I have my script setup N is a parameter passed into the script when it is invoked. It tests to see if it is a number then either grabs that line from a file if it is a number or searches for other files if it is a name. Here's some of the code

#!/bin/bash
input=$1
if [[ `echo $input | grep "[0-9]"` ]]
then
echo `head -n"$input" tempoutput | less -n 1` --this line doesn't work but it shows kinda what I want
else
for name in `find . -iname *$input*`
do
echo "$name" >> tempoutput
done
fi


Thanks,
John

[Rubberman]

This isn't a school assignment, is it?

[ProgramIt]

Nope, this is a project I'm working on for myself. The whole project entails receiving a message from my phone and acting appropriately on it (downloading web pages using a Perl script, checking the status of some of my computers and other such things). It kinda mimics Googles service but extends it further.

- John

[lomcevak]

Take the double quotes out, that's what's wrong:

echo `head -n$input tempoutput | less -n 1`

Also your test for a number is wrong. Anything with a digit in it (like aaa1bbb) will match. You want:

if [[ `echo $input | grep "^[0-9]*$"` ]]

[Rubberman]

Nope, this is a project I'm working on for myself. The whole project entails receiving a message from my phone and acting appropriately on it (downloading web pages using a Perl script, checking the status of some of my computers and other such things). It kinda mimics Googles service but extends it further.

- John

Ok. It's just that the TOS of this site prohibits us from doing school assignments for people, though we can point them in the right direction. You'd be amazed how many people try to get us to do their assignments for them.

As for doing this, my personal approach would be to write a 10 line C or C++ program 'getNthLine' that takes one or more numerical arguments and pulls those lines out of the input file, printing them to stdout. The input could be stdin to keep it simple. You can also use shell, perl, or other scripts to do this (sed would work also, probably better than awk).

[blinky]

try

head -${LINE_NUMBER) $FILE_NAME | tail -1

[ProgramIt]

Thanks for all of your replies got it working just how I wanted.

Also your test for a number is wrong. Anything with a digit in it (like aaa1bbb) will match. You want:

if [[ `echo $input | grep "^[0-9]*$"` ]]

Thanks for the help on my regular expression. I knew it would take things like that for my input but didn't know how to easily fix it so I had just left it like it was. Now it works correctly.

Thanks,
John