Base64 encode implementation entirely in bash

base64encode.sh

#/bin/bash

base64encode(){
    local base64chars="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
    local res=""

    for i in $(seq 0 3 $((${#1}-1)))
    do
        local n1=$(printf '%d' "'${1:i+0:1}")
        local n2=$(printf '%d' "'${1:i+1:1}")
        local n3=$(printf '%d' "'${1:i+2:1}")
        local n=$(( (n1<<16) + (n2<<8) + (n3<<0) ))

        local c1=$(( (n >> 18) & 0x3F ))
        local c2=$(( (n >> 12) & 0x3F ))
        local c3=$(( (n >>  6) & 0x3F ))
        local c4=$(( (n >>  0) & 0x3F ))

        res="$res${base64chars:$c1:1}"
        res="$res${base64chars:$c2:1}"
        res="$res${base64chars:$c3:1}"
        res="$res${base64chars:$c4:1}"
    done

    local mod=$(( (3 - (${#1} % 3)) % 3 ))
    res=${res:0:${#res}-mod}

    while [[ $mod -gt 0 ]]
    do
        res="$res="
        mod=$mod-1
    done

    echo $res
}

base64encode $1