How to split array based on an element value in bash

Question

I have an array say a=(one two three split_array four five). I need to find split_array based on a know substring split and finally get all the items before it i.e one two three. Is there any way to achieve this by using parameter substitution. I can do it using loop but looking for smarter way to achieve this.

Answer 1

I'm not sure if this is smart but you can once concatenate the array into a string and perform the parameter substitution on it:

declare -a a=(one two three split_array four five)
b="${a[*]}"
declare -a c=( ${b%% split_array*} )
for i in ${c[@]}; do
    echo "$i"
done

the output:

one
two
three

• b="${a[*]}" merges the elements of the array to a space-delimited string
• ${b%% split_array*} removes the pattern " split_array*" of $b

Note that the script above is based on the assumption that the elements of the array do not contain IFS characters.

For such a case you can modify the IFS to a character which may not be used in the elements of the array, e.g. the escape character:

ESC=$'\e'       # the escape character
declare -a a=("one word" two three split_array four five)
ifs_bak=$IFS    # back up IFS
IFS=$ESC        # new delimiter
b="${a[*]}"
declare -a c=( ${b%%${ESC}split_array*} )
for ((i=0; i<${#c[@]}; i++)); do
    echo "${c[$i]}"     # test output
done
IFS=$ifs_bak    # retrieve IFS

the output:

one word
two
three

It may not be still 100% guaranteed that the escape character is never used in the array elements. There is always a risk when we merge an array into a string.

Hope this helps.

Answer 2

If you are considering Perl, check this

>  perl -e '@a=qw(one two three split_array four five);for(@a) { last if /split/; print "$_\n" }'
one
two
three
>

If exporting as a variable,

> export a="one two three split_array four five"
> perl -e ' @a=split / /, $ENV{a}; for(@a) { last if /split/; print "$_\n" }'
one
two
three
>