paste <(awk -F, '{print NR,$1}' file1) <(awk -F, '{print $1}' file2) | awk -v var=0 '{ print (($2==$3)?"match":"a[var]="$1); var++}'

> awk '{print NR": "$0}' file1
1: aab
2: b
3: bcbaa
4: ab
5: bb
6: ca
7: ba
8: abacb
9: bccaba

> awk '{print NR": "$0}' file2
1: aab
2: z
3: bcbaa
4: yyz
5: y
6: yx
7: ba
8: abacb
9: z

> bash main.bash
Length: 5
line_numbers[0] = 2
line_numbers[1] = 4
line_numbers[2] = 5
line_numbers[3] = 6
line_numbers[4] = 9