Shell Programming and Scripting

"aaa_b_cc aaa_b_cc_ddd aaa_b_cc aaa_b_cd"

aaa_b_c

aaa_b

function get_common_prefix() {
        list="$1"
        sep="$2"

        printf "$list" | awk '(NR==1) {pcount=split($0,prefix)}
                               (NR>1) {for (i=pcount;i>0;i--) {if ($i!=prefix[i]) {pcount=i-1}}}
                                END {NF=pcount;print}' RS=' ' FS=$sep OFS=$sep
}

myprefix=$(get_common_prefix "$1" $2)

printf "[%s]\n" $myprefix

 A=(aaa_b_cc aaa_b_cc_ddd aaa_b_cc aaa_b_cd)
for ((i=1;i<=${#A[0]}; i++))                            # for the entire first string
  do for ((j=0;j<${#A[@]};j++))                         # for all strngs in array
       do P=${A%${A[0]:$i}}                             # get increasing length substring
          [ "${A[$j]#$P}" = "${A[$j]}" ] && break 2     # test if contained in all strings; if not, no CP, break out
       done
     CP=$P                                              # keep last valid common prefix
  done
echo $CP
aaa_b_c