How to select an element from a 2d array in a file in Linux shell

Question

I am new to shell scripting and what I need is to read from a file that contains a 2d array. Assume there is a file named test.dat which contains values as:

- Paris         London     Lisbon
- Manchester    Nurnberg   Istanbul
- Stockholm     Kopenhag   Berlin

What is the easiest way to select an element from this table in linux bash scripts? For example, the user inputs -r 2 -c 2 test.dat that implies to selecting the element at row[2] and column[2] (Nurnberg).

I have seen the read command and googled but most of the examples were about 1d array.

This one looks familiar but could not understand it exactly.

fedorqui · Accepted Answer · 2014-01-15 14:37:49Z

1

awk is great for this:

$ awk 'NR==row{print $col}' row=2 col=2 file
Nurnberg

NR==row{} means: on number of record number row, do {} Number of record normally is the number of line.
{print $col} means: print the field number col.
row=2 col=2 is giving both parameters to awk.

Update

One more little question: How can I transform this into a sh file so that when I enter -r 2 -c 2 test.dat into prompt, I get to run the script so that it reads from the file and echoes the output? – iso_9001_.

For example:

#!/bin/bash

file=$1
row=$2
col=$3

awk 'NR==row{print $col}' row=$row col=$col $file

And you execute like:

./script a 3 2
Kopenhag

edited Jan 15, 2014 at 14:37

answered Jan 15, 2014 at 10:25

fedorqui

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9 Comments

iso_9001_ Over a year ago

Great! I was suspecting awt would work :) Thank you very much

fedorqui Over a year ago

awk is sooooo powerful for this kind of things :) Glad it worked to you!

iso_9001_ Over a year ago

One more little question: How can I transform this into a sh file so that when I enter -r 2 -c 2 test.dat into prompt, I get to run the script so that it reads from the file and echoes the output?

iso_9001_ Over a year ago

You are really fast and have been very helpful :) thank you very much

iso_9001_ Over a year ago

Today, I have successfully managed to write the code as you suggested. So, thanks again. What I now lack is, I can manage to run the code as ./tablooku.sh tablom.dat 2 2 but when I try to parameterize "2 2" part as ./tablooku.sh tablom.dat -r 2 -c 2 I get my error message that says "Error: -rth row and -cth column does not exist". How can I parameterize the command?

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