Can the cut command accept newline as a delimiter? - bash

Question

I have a file, foo.txt, with 2 lines:
foo bar
hello world
I am trying to output the second line using:
cut -d$'\n' -f2 foo.txt
But it is printing both lines instead.
Is cut able to accept a newline as a delimiter?

Answer 1

Background
cut operates on all lines of the input, so I don't think that a newline can
work as a delimiter.
From cut(1p) of POSIX.1-2017:
NAME
cut - cut out selected fields of each line of a file
SYNOPSIS
cut -b list [-n] [file...]
cut -c list [file...]
cut -f list [-d delim] [-s] [file...]
DESCRIPTION
The cut utility shall cut out bytes (-b option), characters (-c option), or
character-delimited fields ( -f option) from each line in one or more
files, concatenate them, and write them to standard output.
Example:
$ printf 'foo bar1\nfoo bar2\n'
foo bar1
foo bar2
$ printf 'foo bar1\nfoo bar2\n' | cut -f 2 -d ' '
bar1
bar2
Solution
To print only the second line of input, sed can be used:
$ printf 'foo bar1\nfoo bar2\n'
foo bar1
foo bar2
$ printf 'foo bar1\nfoo bar2\n' | sed '2p;d'
foo bar2

Answer 2

It's not very clear what you want, but this is splitting on empty lines and collapsing the others using awk:
awk 'BEGIN {RS=""} {gsub("\n",""); print}'

Answer 3

this might not be a very elegant solution, but i often just use head and tail, since they typically outperform sed or awk in speed
#!/bin/sh
input='test0\ntest1\ntest2\ntest3\ntest4\ntest5'
echo -e "$input" | head --lines 3
# test0
# test1
# test2
echo -e "$input" | tail --lines 3
# test3
# test4
# test5
get_index() {
echo -e "$1" |
head --lines "$(( $2 + 1 ))" |
tail --lines "1"
}
get_index "$input" "0"
# test0
get_index "$input" "4"
# test4