Linux SHELL script, read each row for different number of columns

Question

I have file and for example values in it:

1 value1.1 value1.2
2 value2.1
3 value3.1 value3.2 value3.3

I need to read values using the shell script from it but number of columns in each row is different!!! I know that if for example I want to read second column I will do it like this (for row number as input parameter)

$ awk -v key=1 '$1 == key { print $2 }' input.txt
value1.1

But as I mentioned number of columns is different for each row. How to make this read dynamic?

For example: if input parameter is 1 it means I should read columns from the first row so output should be

value1.1 value1.2

if input parameter is 2 it means I should read columns from the second row so output should be

value2.1

if input parameter is 3 it means I should read columns from the third row so output should be

value3.1 value3.2 value3.2

Th point is that number of columns is not static and I should read columns from that specific row until the end of the row.

Thank you

What does "dynamic" mean specifically, to you? What do you want to happen when your "second column reader" encounters a one-column row? — Amadan
– Amadan, Commented Nov 13, 2018 at 7:05
@Dejan, please do mention expected sample output too in your post. — RavinderSingh13
– RavinderSingh13, Commented Nov 13, 2018 at 7:13
There's no problem reading varaible #columns. The point is what you want to do with them. It will be appreciated if you can illustrate with example data and expected output. — tshiono
– tshiono, Commented Nov 13, 2018 at 7:14

tshiono · Accepted Answer · 2018-11-13 08:59:42Z

3

Then you can simply say:

awk -v key=1 'NR==key' input.txt

UPDATED

If you want to process with the column data, there will be several ways.
With awk you can say something like:

awk -v key=3 'NR==key {
    for (i=1; i<=NF; i++)
        printf "column %d = %s\n", i, $i
}' input.txt

which outputs:

column 1 = value3.1
column 2 = value3.2
column 3 = value3.2

In awk you can access each column value by $1, $2, $3 directly or by $i indirectly where variable i holds either of 1, 2, 3.

If you prefer going with bash, try something like:

line=$(awk -v key=3 'NR==key' input.txt)
set -- $line    # split into columns

for ((i=1; i<=$#; i++)); do
    echo column $i = ${!i}
done

which outputs the same results.
In bash the indirect access is a little bit complex and you need to say ${!i} where i is a variable name.

Hope this helps.

edited Nov 13, 2018 at 8:59

answered Nov 13, 2018 at 7:32

tshiono

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3 Comments

Veljko Over a year ago

thanks. And just one small question - how can I read value by value when I have output for example for the third column value3.1 value3.2 value3.2 and now I would like to process one value by one (I need to take and parse one value by one)

Veljko Over a year ago

please if you can just add how to read value by value - one by one from this output (for example value3.1 value3.2 value3.3)

tshiono Over a year ago

I updated my answer. Please take a look and if something is unclear please let me know.

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