Base64, URL encoding, hashes, UUIDs and Unix timestamps: the one-liners I kept looking up

Saman — Thu, 29 Oct 2026 06:24:10 +0000

Every few days I need to Base64 a file, hash a download, or turn an epoch value into a date, and every few days I search for the exact same one-liner. So I finally wrote them down in one place. Copy what you need.

Base64

Where	Encode	Decode
Linux / macOS	`base64 file.png`	`base64 -d encoded.txt` (`-D` on older macOS)
PowerShell	`[Convert]::ToBase64String([IO.File]::ReadAllBytes('file.png'))`	`[Convert]::FromBase64String($s)`
Python	`base64.b64encode(data)`	`base64.b64decode(s)`
Browser JS	`btoa(str)`	`atob(s)`
Node.js	`Buffer.from(str).toString('base64')`	`Buffer.from(s, 'base64')`
PHP	`base64_encode($data)`	`base64_decode($s)`

Gotcha: btoa only accepts Latin-1. Text with accents or emoji needs a TextEncoder step first, or it throws.

URL encoding

Language	Encode one value	Watch out
JavaScript	`encodeURIComponent(value)`	`encodeURI` is for a whole address
Python	`urllib.parse.quote(value, safe='')`	`quote_plus` turns spaces into `+`
PHP	`rawurlencode($value)`	`urlencode` uses `+` for spaces
Java	`URLEncoder.encode(value, "UTF-8")`	produces `+`; use `%20` inside a path
C#	`Uri.EscapeDataString(value)`	`HttpUtility.UrlEncode` uses `+`

Gotcha: if you see %2520, the value was encoded twice. Decode once, encode once.

File hashes (checking a download)

System	SHA-256	MD5
Windows cmd	`certutil -hashfile file.iso SHA256`	`certutil -hashfile file.iso MD5`
PowerShell	`Get-FileHash file.iso -Algorithm SHA256`	`Get-FileHash file.iso -Algorithm MD5`
Linux	`sha256sum file.iso`	`md5sum file.iso`
macOS	`shasum -a 256 file.iso`	`md5 file.iso`
Python	`hashlib.sha256(data).hexdigest()`	`hashlib.md5(data).hexdigest()`

The result is identical everywhere: a hash depends only on the bytes, never on the tool.

UUIDs

Platform	One-liner
JavaScript	`crypto.randomUUID()`
Python	`import uuid; uuid.uuid4()`
Java	`UUID.randomUUID()`
C#	`Guid.NewGuid()` (`Guid.CreateVersion7()` on .NET 9)
PostgreSQL	`gen_random_uuid()` (`uuidv7()` from PostgreSQL 18)
MySQL	`UUID()` (careful: this is a time-based v1)
Shell	`uuidgen`

Gotcha: for database primary keys, prefer v7. It starts with a millisecond timestamp, so new rows land at the end of the index instead of scattering through it.

Unix timestamps

Where	Now	Timestamp to date
JavaScript	`Math.floor(Date.now() / 1000)`	`new Date(ts * 1000)`
Python	`int(time.time())`	`datetime.fromtimestamp(ts, tz=timezone.utc)`
PHP	`time()`	`date('Y-m-d H:i:s', $ts)`
MySQL	`UNIX_TIMESTAMP()`	`FROM_UNIXTIME(ts)`
PostgreSQL	`EXTRACT(EPOCH FROM now())`	`to_timestamp(ts)`
Shell	`date +%s`	`date -d @1700000000` (`date -r 1700000000` on macOS)
Excel	–	`=A1/86400 + DATE(1970,1,1)` (UTC)

Gotcha: 10 digits is seconds, 13 digits is milliseconds. A date in 1970 means you passed milliseconds where seconds were expected, or the other way round.

Discord bonus: <t:1700000000:R> renders as a relative time in every reader's own time zone.