Linux Shell脚本：以指定方式从字符串中提取值

Question

I have one variable contain values like:

USER1:USER2,USER3:USER4,USER5:USER6

I want to extract values like USER1,USER3,USER5

For Example:

VALUE = USER1:USER2,USER3:USER4,USER5:USER6

how I echo to extract like this

USER1,USER3,USER5

Answer 1

#!/bin/bash

string=USER1:USER2,USER3:USER4,USER5:USER6
IFS=', ' read -r -a array <<< "$string"
output=

for kv in ${array[@]}; do
    key=$(echo $kv | cut -d':' -f1)
    output="$output,$key"
done

output=$(echo $output | cut -c 2-)
echo $output