Reference
Tables and cheat sheets to keep open in a tab or print.
HTTP status codesEvery status code with what it means and when you actually see it, including Cloudflare’s 52x502 = the proxy got nothing usable from the backendASCII tableAll 128 ASCII codes in decimal, hex, octal and binary, with control characters, Ctrl keys, HTML and URL formsA = 65 = 0x41 = 0101Bitwise tricks cheat sheetThe 30 bit-manipulation idioms worth knowing, with one-line explanationschmod & permissions cheat sheetOctal and symbolic chmod, special bits, umask, chown, ACLs, on one pageCron cheat sheetCrontab syntax, the 25 schedules everyone needs, environment gotchas and the commandsSubnet cheat sheetIPv4 prefix table /0–/32 with masks, wildcards and host counts; private ranges; IPv6 essentialsBase64 & encodings cheat sheetThe Base64, Base64URL, Base32 and hex alphabets, padding rules, sizes, and the commands in every languageRegex cheat sheetMetacharacters, classes, quantifiers, groups, lookarounds, flags and the flavour differences, on one page