.tip

May 12, 2026 · one of the small things

trap cleans up temp files even when the script dies

A script that creates a temp directory and deletes it at the end leaves the directory behind every time it exits early. trap runs the cleanup on any exit.

tmp=$(mktemp -d)
trap 'rm -rf "$tmp"' EXIT

EXIT fires on success, on an error under set -e, and on Ctrl-C, so the file system stays clean whichever way it ends.

shell

~/tips/today — 2026-10-19

~cat tips/today

Never build an index on a live table without CONCURRENTLY

postgresqlmigrations

A plain CREATE INDEX takes a lock that blocks every write to the table for the whole build. On a big table that means minutes of outage that look like a hung app.

CREATE INDEX CONCURRENTLY orders_customer_idx ON orders (customer_id);

It's slower and can't run inside a transaction, so you'll have to tell your migration tool. If it fails halfway, it leaves an invalid index behind, so check pg_index.indisvalid and drop it before you retry.

↵ open y yesterday l ls /tips

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