Base64 인코딩·디코딩, macOS 터미널로 직접 해 보니

$ printf 'Hello' | base64 && printf 'SGVsbG8=' | base64 -d && echo && printf 'Hi' | base64 && printf 'H' | base64
SGVsbG8=
Hello
SGk=
SA==

$ base64 --version && base64 -h
FreeBSD base64
Usage:	base64 [-Ddh] [-b num] [-i in_file] [-o out_file]
  -b, --break       break encoded output up into lines of length num
  -D, -d, --decode  decode input
  -h, --help        display this message
  -i, --input       input file (default: "-" for stdin)
  -o, --output      output file (default: "-" for stdout)

$ printf '안녕하세요 솔로개발노트' | wc -c && printf '안녕하세요 솔로개발노트' | base64 && printf '안녕하세요 솔로개발노트' | iconv -f UTF-8 -t EUC-KR | wc -c && printf '안녕하세요 솔로개발노트' | iconv -f UTF-8 -t EUC-KR | base64
      34
7JWI64WV7ZWY7IS47JqUIOyGlOuhnOqwnOuwnOuFuO2KuA==
      23
vsiz58fPvLy/5CC81rfOsLO537Prxq4=

$ for f in icon.png photo.jpg photo.webp; do base64 -i $f -o $f.b64; o=$(wc -c < $f); e=$(tr -d '\n' < $f.b64 | wc -c); awk -v f=$f -v o=$o -v e=$e 'BEGIN { printf "%s 원본 %d바이트 → Base64 %d바이트 (%.1f%% 늘어남)\n", f, o, e, (e / o - 1) * 100 }'; done
icon.png 원본 1396바이트 → Base64 1864바이트 (33.5% 늘어남)
photo.jpg 원본 196404바이트 → Base64 261872바이트 (33.3% 늘어남)
photo.webp 원본 87006바이트 → Base64 116008바이트 (33.3% 늘어남)

$ base64 -b 76 -i icon.png -o icon76.b64 && head -3 icon76.b64 && wc -l < icon76.b64 && wc -l < icon.png.b64
iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAYAAABzenr0AAAABGdBTUEAALGPC/xhBQAAACBjSFJN
AAB6JgAAgIQAAPoAAACA6AAAdTAAAOpgAAA6mAAAF3CculE8AAAAeGVYSWZNTQAqAAAACAAEARoA
BQAAAAEAAAA+ARsABQAAAAEAAABGASgAAwAAAAEAAgAAh2kABAAAAAEAAABOAAAAAAAAAJAAAAAB
      25
       1

$ printf 'base64          '; base64 -i photo.jpg | shasum -a 256 | cut -c1-16
printf 'openssl         '; openssl base64 -in photo.jpg | shasum -a 256 | cut -c1-16
printf 'openssl -A      '; openssl base64 -A -in photo.jpg | shasum -a 256 | cut -c1-16
printf 'python3         '; python3 -c "import base64, sys; sys.stdout.write(base64.b64encode(open('photo.jpg', 'rb').read()).decode())" | shasum -a 256 | cut -c1-16
printf 'node            '; node -e "process.stdout.write(require('fs').readFileSync('photo.jpg').toString('base64'))" | shasum -a 256 | cut -c1-16
base64          45f49d6fb7054f5f
openssl         bf5a70646176b1ba
openssl -A      7d251edc6a9b08db
python3         7d251edc6a9b08db
node            7d251edc6a9b08db

$ tail -c 3 photo.jpg.b64 | xxd && openssl base64 -in photo.jpg -out photo.ossl && head -2 photo.ossl && wc -l < photo.ossl
printf '줄바꿈을 지운 base64  '; tr -d '\n' < photo.jpg.b64 | shasum -a 256 | cut -c1-16
printf '줄바꿈을 지운 openssl '; tr -d '\n' < photo.ossl | shasum -a 256 | cut -c1-16
00000000: 2f5a 0a                                  /Z.
/9j/4AAQSkZJRgABAQAASABIAAD/4QBMRXhpZgAATU0AKgAAAAgAAYdpAAQAAAAB
AAAAGgAAAAAAA6ABAAMAAAABAAEAAKACAAQAAAABAAAEsKADAAQAAAABAAACeQAA
    4092
줄바꿈을 지운 base64  7d251edc6a9b08db
줄바꿈을 지운 openssl 7d251edc6a9b08db

$ for f in photo.jpg icon.png; do printf '%s 원본 %s, gzip %s / Base64 %s, gzip %s\n' $f $(wc -c < $f) $(gzip -9 -c $f | wc -c) $(tr -d '\n' < $f.b64 | wc -c) $(tr -d '\n' < $f.b64 | gzip -9 | wc -c); done
photo.jpg 원본 196404, gzip 195845 / Base64 261872, gzip 197557
icon.png 원본 1396, gzip 1182 / Base64 1864, gzip 1272

$ printf '<img src="photo.jpg" width="600">' > external.html && printf '<img src="data:image/jpeg;base64,%s" width="600">' "$(tr -d '\n' < photo.jpg.b64)" > inline.html && ls -l external.html inline.html | awk '{print $5, $9}'
for p in external inline; do "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" --headless --disable-gpu --hide-scrollbars --user-data-dir="$PWD/chrome-profile" --window-size=640,360 --screenshot="$PWD/$p.png" "file://$PWD/$p.html" >/dev/null 2>&1; done
shasum -a 256 external.png inline.png | cut -c1-16
33 external.html
261919 inline.html
0f7d97a95b2b36b5
0f7d97a95b2b36b5

$ python3 -c "import base64; print(base64.b64decode('SGVsbG8'))"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import base64; print(base64.b64decode('SGVsbG8'))
                         ~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.15/3.15.0_1/Frameworks/Python.framework/Versions/3.15/lib/python3.15/base64.py", line 117, in b64decode
    result = binascii.a2b_base64(s, strict_mode=validate,
                                 padded=padded, ignorechars=ignorechars,
                                 canonical=canonical)
binascii.Error: Incorrect padding

$ printf 'SGVsbG8' | base64 -d; echo " (종료 코드 $?)"
python3 -c "import base64; s = 'SGVsbG8'; print(base64.b64decode(s + '=' * (-len(s) % 4)))"
Hel (종료 코드 0)
b'Hello'

$ printf '\xfb\xff\xbf' | base64 && python3 -c "import base64; print(base64.urlsafe_b64encode(bytes([0xfb, 0xff, 0xbf])).decode())" && python3 -c "import base64; print(base64.b64decode('-_-_'))" && python3 -c "import base64; print(base64.urlsafe_b64decode('-_-_'))" && python3 -c "import base64
try:
    base64.b64decode('-_-_', validate=True)
except Exception as e:
    print(type(e).__name__ + ':', e)"
+/+/
-_-_
b''
b'\xfb\xff\xbf'
Error: Only base64 data is allowed

$ node -e "console.log(btoa('Hello'))" && node -e "try { btoa('안녕') } catch (e) { console.log(e.name + ': ' + e.message) }" && node -e "const b = new TextEncoder().encode('안녕'); console.log(btoa(String.fromCharCode(...b)))" && node -e "console.log(Buffer.from('안녕').toString('base64'))" && printf '안녕' | base64
SGVsbG8=
InvalidCharacterError: Invalid character
7JWI64WV
7JWI64WV
7JWI64WV

$ seq 1 30 > note.txt && wc -c < note.txt && jq -n --arg data "$(openssl base64 -in note.txt)" '{data: $data}' && jq -n --arg data "$(openssl base64 -A -in note.txt)" '{data: $data}'
      81
{
  "data": "MQoyCjMKNAo1CjYKNwo4CjkKMTAKMTEKMTIKMTMKMTQKMTUKMTYKMTcKMTgKMTkK\nMjAKMjEKMjIKMjMKMjQKMjUKMjYKMjcKMjgKMjkKMzAK"
}
{
  "data": "MQoyCjMKNAo1CjYKNwo4CjkKMTAKMTEKMTIKMTMKMTQKMTUKMTYKMTcKMTgKMTkKMjAKMjEKMjIKMjMKMjQKMjUKMjYKMjcKMjgKMjkKMzAK"
}

$ claude --model opus -p "맥 터미널에서 icon.png 파일을 HTML img 태그의 src에 넣을 수 있는 data URI 문자열(data:image/png;base64,...)로 바꿔 icon.txt에 저장하는 명령 한 줄만 출력해. 설명이나 코드 블록 표시는 붙이지 마." < /dev/null > cmd.txt && cat cmd.txt && sh cmd.txt && head -c 60 icon.txt && echo && wc -c < icon.txt
printf 'data:image/png;base64,%s' "$(base64 -i icon.png)" > icon.txt
data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAYAAA
    1886