Parameter expansion in bash for loop to retreive key and value-CodePudding

I'm not sure what is doing this for loop in Bash that is using this kind of parameter expansions var_key="${env%%=*}"

    for env in "${envvars[@]}"; do
        var_key="${env%%=*}"
        var_value="${env#*=}"
        if [[ -z ${!var_key} ]]; then
            echo "export ${env}" >> "${FILE}"
            echo "export ${var_key}=\"${var_value}\"" >> "${FILE}"
        fi
    done

Any idea of what is being doing this for loop.

CodePudding user response：

"${env%%=*}" is one possible form of a "parameter expansion". It removes the longest match of the pattern =* from the value of the variable $env. # is similar but operates on the beginning of the value.

E.g.

env=x=3=6
echo ${env%%=*}  # x
echo ${env%=*}   # x=3
echo ${env#*=})  # 3=6
echo ${env##*=}) # 6