Linux
Dockerfile Layer Caching: Order Instructions for Fast Rebuilds
A one-line code change should not reinstall every dependency. Timed rebuilds show how instruction order, .dockerignore and ARG placement decide what Docker reuses.
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Web
HTTP Cache-Control Explained: max-age, no-cache, ETags
no-cache does not mean do not cache. A hands-on look at Cache-Control, ETags and 304 responses with a tiny Node server, plus how a CDN treats them.
Programming
Python venv in Practice: Create, Use and Rebuild
How I use python -m venv on servers and laptops: one environment per project, pinned requirements, no activation in cron, and why .venv never goes into Git.
Linux
Find Which Process Is Listening on a Port in Linux
"Address already in use" again? How to find the owner of a port with ss, lsof and fuser, decode /proc/net/tcp by hand, and why some ports show no process.
Programming
PHP 8 match Expression vs switch: Differences That Bite
match looks like a shorter switch, but it compares strictly, never falls through, returns a value and throws when nothing matches. Here is what that means in practice.
Programming
How to Undo the Last Git Commit (and Recover From It)
amend, reset --soft, --mixed, --hard, revert and restore each undo something different. A tested walk-through, plus how the reflog recovers from a bad reset.
MySQL
ipcalc() in MySQL: Network, Broadcast and Prefix From a Netmask
Work out the network, broadcast address and prefix length of an IPv4 address inside a query, using INET_ATON(), INET_NTOA() and a little bitwise arithmetic.
Bash
__pgrepf() in Bash: pgrep -f Using Only /proc
Find processes by their full command line in pure Bash by reading /proc/PID/cmdline, with the NUL bytes handled properly and the 2009 bugs fixed.
Bash
emptydir() in Bash: Check Whether a Directory Is Empty
Test whether a directory is empty in pure Bash with nullglob and dotglob, handle hidden and unreadable directories, and know when find -quit is faster.
Bash
strlen() in Bash: Get the Length of a String
Bash's ${#var} counts characters, PHP's strlen() counts bytes. A clean strlen() function, a strbytes() companion, and the locale traps in between.