Merging two arrays in Bash


Question

I have the following situation, two arrays, let's call them A( 0 1 ) and B ( 1 2 ), i need to combine them in a new array C ( 0:1 0:2 1:1 1:2 ), the latest bit i've come up with is this loop:

   for ((z = 0; z <= ${#A[@]}; z++)); do
     for ((y = 0; y <= ${#B[@]}; y++)); do
       C[$y + $z]="${A[$z]}:"
       C[$y + $z + 1]="${B[$y]}"
     done
   done

But it doesn't work that well, as the output i get this:

 0: : : :

In this case the output should be 0:1 0:2 as A = ( 0 ) and B = ( 1 2 )

1
22
2/4/2017 5:36:15 AM

Accepted Answer

Since Bash supports sparse arrays, it's better to iterate over the array than to use an index based on the size.

a=(0 1); b=(2 3)
i=0
for z in ${a[@]}
do
    for y in ${b[@]}
    do
        c[i++]="$z:$y"
    done
done
declare -p c   # dump the array

Outputs:

declare -a c='([0]="0:2" [1]="0:3" [2]="1:2" [3]="1:3")'
12
12/31/2009 4:47:58 PM

If you don't care about duplicates, you can concatenate the two arrays in one line with:

NEW=("${OLD1[@]}" "${OLD2[@]}")

Full example:

Unix=('Debian' 'Red hat' 'Ubuntu' 'Suse' 'Fedora' 'UTS' 'OpenLinux');
Shell=('bash' 'csh' 'jsh' 'rsh' 'ksh' 'rc' 'tcsh');
UnixShell=("${Unix[@]}" "${Shell[@]}")
echo ${UnixShell[@]}
echo ${#UnixShell[@]}

Credit: http://www.thegeekstuff.com/2010/06/bash-array-tutorial/


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