Delete newlines from all elements of a array in shell - arrays

Question

I try to solve a problem in shell.
Im trying to find a way to delete all newlines from each element of an array. I tried to do this with a for loop.
The Strings look like this (always three numbers, separated with dots)
"14.1.3\n" and I need to get rid of the newline at the end.
This is what i tried to do:
As a single-liner
for i in ${backup_versions[*]}; do backup_versions[$i]=echo "$i" | tr '\n' ' ' ; done
Easier to read
for i in ${backup_versions[*]};
do
backup_versions[$i]=echo "$i" | tr '\n' ' '
done
I think I try to reassign the element with the wrong syntax, but I tried every kind of writing i which I found or knew myself.
The deletion of the newline works just fine and just the reassigning is my Problem.

Answer 1

If the strings are always of that form and don't contain any whitespace or wildcard characters, you can just use the shell's word-splitting to remove extraneous whitespace characters from the values.
backup_versions=(${backup_versions[*]})
If you used mapfile to create the array, you can use the -t option to prevent it from including the newline in the value in the first place.

Answer 2

Use Bash's string substitution expansion ${var//old/new} to delete all newlines, and dynamically create a declaration for a new array, with elements stripped of newlines:
#!/usr/bin/env bash
backup_versions=(
$'foo\nbar\n'
$'\nbaz\ncux\n\n'
$'I have spaces\n and newlines\n'
$'It\'s a \n\n\nsingle quote and spaces\n'
$'Quoted "foo bar"\n and newline'
)
# shellcheck disable=SC2155 # Dynamically generated declaration
declare -a no_newlines="($(
printf '%q ' "${backup_versions[#]//$'\n'/}"
))"
# Debug print original array declaration
declare -p backup_versions
# Debug print the declaration of no_newlines
declare -p no_newlines
declare -a no_newlines="($(: Creates a dynamically generated declaration for the no_newlines array.
printf '%q ': Print each argument with quotes if necessary and add a trailing space.
"${backup_versions[#]//$'\n'/}": Expand each element of the backup_versions array, // replacing all $'\n' newlines by nothing to delete them.
Finally the no_newlines array will contain all entries from backup_versions, with newlines stripped-out.
Debug output match expectations:
declare -a backup_versions=([0]=$'foo\nbar\n' [1]=$'\nbaz\ncux\n\n' [2]=$'I have spaces\n and newlines\n' [3]=$'It\'s a \n\n\nsingle quote and spaces\n' [4]=$'Quoted "foo bar"\n and newline')
declare -a no_newlines=([0]="foobar" [1]="bazcux" [2]="I have spaces and newlines" [3]="It's a single quote and spaces" [4]="Quoted \"foo bar\" and newline")

Answer 3

You can use a modifier when expanding the array, then save the modified contents. If the elements just have a single trailing newline, use substring removal to trim it:
backup_versions=("${backup_versions[#]%$'\n'}")
(Note: when expanding an array, you should almost always use [#] instead of [*], and put double-quotes around it to avoid weird parsing. Bash doesn't generally let you combine modifiers, but you can combo them with [#] to apply the modifier to each element as it's expanded.)
If you want to remove all newlines from the elements (in case there are multiple newlines in some elements), use a substitution (with an empty replacement string) instead:
backup_versions=("${backup_versions[#]//$'\n'/}")
(But as several comments have mentioned, it'd probably be better to look at how the array's being created, and see if it's possible to just avoid putting newlines in the array in the first place.)