base64 encoder given by build-in linux commands.

base64sh.sh

base64sh() {
    local input=${1:-$(cat)}
    paste <(seq 0 63 | sed 's/^/obase=2;ibase=10;/' | bc | sed 's/^/00000/' | grep -oE '.{6}$') \
    <(echo {A..Z} {a..z} {0..9} + / | xargs -n 1) | \
    awk '{print "s|"$1"|"$2"|"}' | \
    sed -f - <(echo -n $input| perl -ne 'print unpack("B*", $_)."0000"' | \
    fold -w 6 | grep -oE '.{6}$') | tr -d '\n' | fold -w 4 | sed 's/$/===/' | grep -oE '^.{4}' | tr -d '\n' | awk 1
}

# Usage: base64sh
#
# $ echo Yes高須クリニック | base64sh
# WWVz6auY6aCI44Kv44Oq44OL44OD44Kv
#
# $ base64sh 'This is a pen'
# VGhpcw==
#