Unix script with variable parameters

Question

So i am wring a script that would take several files, compare them and then output the different records.

The script is working fine for 3 parameter ( 3 files ), but i am having trouble to make the parameters vary.

Consider the script is named Test.

If i write: Test 1.txt 2.txt, The script will know that i have 2 inputs, which are 2 files and will compare them and give me an output.

Furthermore, if i write Test 1.txt 2.txt 3.txt, The script will know that i have 3 inputs, which are 3 files, compare them and give me an output.

The script now has the following commands :

awk 'NR>2' ${1} | awk '{print $NF "\r"}' > N1
awk 'NR>2' ${2} | awk '{print $NF "\r"}' > N2
awk 'NR>2' ${3} | awk '{print $NF "\r"}' > N3

This is working fine for 3 files, but the problem is that sometimes i have 2 files, sometimes i have 4 files.

I know i can fix that using loops, but i am new to this language and not very familiar with the syntax.

Thank you for your help :)

Farvardin · Accepted Answer · 2014-07-23 10:49:07Z

2

use this :

x=1
for i in "$@"
do
  awk 'NR>2' $i | awk '{print $NF "\r"}' > N$x
  x=$(($x+1))
done

$@ : list of input parameters

edited Jul 23, 2014 at 10:49

answered Jul 23, 2014 at 10:03

Farvardin

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3 Comments

jaybee Over a year ago

Nice short answer! Please note that incrementing x can also be written ((x++)), a shorter syntax which is easier to remember for all programmers :)

tripleee Over a year ago

This is wrong, but easy to fix. You specifically must use double quotes around $@ in order for quoted arguments to work properly.

glenn jackman Over a year ago

@Necro1992 Take tripleee's advice and quote "$@" -- it will break the first time you use a filename with a space.

glenn jackman · Accepted Answer · 2014-07-23 10:54:41Z

1

Your awk commands can be combined: awk 'NR>2 {print $NF "\r"}' "$1" > N1.

Better yet, a single awk command to process all files:

awk '
    FNR == 1 {output = "N" ++count}
    FNR > 2  {print $NF "\r" > output}
' "$@"

"One awk to rule them all"

answered Jul 23, 2014 at 10:54

glenn jackman

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