Shell Programming and Scripting

What about:

Code:

echo "$var" > list.txt

Or use "sed" to copy lines 2 onwards, then get the first line with "head -1".

#!/bin/ksh
cat list.txt | sed -n "2,\$ p" >new_list.txt
head -1 list.txt >> new_list.txt

This is UUOC, cat is not needed here

just sed '<operation>' filename would do

Nor is head required:

Code:

IFS= read -r line < list.txt
printf "%s\n" "$line" >> new_list.txt

It is possible to write scripts which might work efficiently but are unintelligible to newbies. The previous post with "IFS" is a classic.
We may post examples which are easy to follow rather than what we might use in a commercial environment. Most people find left-to-right date flow easier to follow.

IMHO the best outline design is the compact "awk" program which the poster tried but got the wrong results. It needs adjusting to not put the whole file into a variable called $var, but to write directly to the new file instead. This could be done from "awk" itself, but here is a way with shell redirect.

awk 'NR==1{store=$0;next}1;END{print store}' list.txt >new_list.txt

In a production script you would probably then copy "list.txt" before overwriting it with "new_list.txt" .

Its better to get various forms of getting it to work, as the saying goes " many ways to skin a cat " ( no uuoc here )

Initially for a newbie it might be of interest to get the task done and later it might be interesting and a good learning experience to make it better, optimal without having to spawn too many processes where it could be achieved by shell built-ins etc.

I fully agree with matrixmadham. Whether on unix , DOS, VME or whatever building shell programs is best learnt step-by-step with prototype scripts and examples which can then be improved with experience.
Each year we will find a move towards a fashionable standard. Whatever happened to OS-9 and DCL as universal scripting languages? We are learning from cfajohnson of a move towards Posix-2 , but to get "normal" Berkeley behaviour from commands such as "ps" and "xd" we often need to go outside Posix-2 and even the less-strict XPG4 standard.

When we work on multiple unix/Linux/etc. platforms it is useful to learn portable scripting techniques and to be aware of useful commands that are not always implemented like Linux "stat", or can have differerent syntax like "echo", or can have a mishmash of variations like "awk" and "nawk".

IMHO we will still be debating standards up to 18/01/2038 (the Y2K38 problem).