How to read n-th line from a text file in bash?

Question

Say I have a text file called "demo.txt" who looks like this:

1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16

Now I want to read a certain line, say line 2, with a command which will look something like this:

Line2 = read 2 "demo.txt"

So when I'll print it:

echo "$Line2"

I'll get:

5 6 7 8

I know how to use 'sed' command in order to print a n-th line from a file, but not how to read it. I also know the 'read' command but dont know how to use it in order a certain line.

Thanks in advance for the help.

possible duplicate of [bash tool to get nth line from a file](http://stackoverflow.com/questions/6022384/bash-tool-to-get-nth-line-from-a-file) — tripleee, Nov 21 '14 at 11:05

nu11p01n73R · Accepted Answer · 2014-11-21T11:02:05.310

28

Using head and tail

$ head -2 inputFile | tail -1
5 6 7 8

OR

a generalized version

$ line=2
$ head -"$line" input | tail -1
5 6 7 8

Using sed

$ sed -n '2 p' input
5 6 7 8
$  sed -n "$line p" input
5 6 7 8

What it does?

-n suppresses normal printing of pattern space.
'2 p' specifies the line number, 2 or ($line for more general), p commands to print the current patternspace
input input file

Edit

To get the output to some variable use some command substitution techniques.

$ content=`sed -n "$line p" input`
$ echo $content
5 6 7 8

OR

$ content=$(sed -n "$line p" input)
$ echo $content
5 6 7 8

To obtain the output to a bash array

$ content= ( $(sed -n "$line p" input) )
$ echo ${content[0]}
5
$ echo ${content[1]}
6

Using awk

Perhaps an awk solution might look like

$  awk -v line=$line 'NR==line' input
5 6 7 8

Thanks to Fredrik Pihl for the suggestion.

edited Nov 21 '14 at 11:02

answered Nov 21 '14 at 08:21

nu11p01n73R

26,397
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52

You need to get output to variable? – nu11p01n73R Nov 21 '14 at 08:27
1

Only tool that is missing from your answer is `awk`, perhaps add a `awk -v line=$line 'NR==line'` for completeness. – Fredrik Pihl Nov 21 '14 at 08:37
@FredrikPihl Thanks for the suggestion. Included in the answer :) – nu11p01n73R Nov 21 '14 at 08:51
Anyway to read it as an array like being done with 'read'? For example, I want ${line[0]}=5 and ${line[1]}=6 and so on... – user3206874 Nov 21 '14 at 10:50
@user3206874 you mean to get the output to an array for that wrap the command in `()` like `content=( $(sed -n "$line p" input) )`. Now `${content[0]}` is 5 `${content[1]}` is 6 – nu11p01n73R Nov 21 '14 at 10:56

score 0 · Answer 2 · answered Sep 06 '22 at 16:46

Perl has convenient support for this, too, and it's actually the most intuitive!

The flip-flop operator can be used with line numbers:

$ printf "0\n1\n2\n3\n4" | perl -ne 'printf if 2 .. 4'
1
2
3

Note that it's 1-based.

You can also mix regular expressions:

$ printf "0\n1\nfoo\n3\n4" | perl -ne 'printf if /foo/ .. -1'
foo
3
4

(-1 refers to the last line)

How to read n-th line from a text file in bash?

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