This is a story about how I tried to use PostgreSQL after a long time, ran the psql command, got a Library not loaded: libreadline error, and resolved it by running brew upgrade postgresql.

Library not loaded: libreadline error when running psql command

$ psql
dyld: Library not loaded: /usr/local/opt/readline/lib/libreadline.6.2.dylib
  Referenced from: /usr/local/bin/psql
  Reason: image not found
[1]    61053 trace trap  psql

Upgrade PostgreSQL version with brew upgrade postgresql

brew update
brew upgrade postgresql
launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
mv /usr/local/var/postgres /usr/local/var/postgres9.3.1
initdb /usr/local/var/postgres
pg_upgrade \\
  -b /usr/local/Cellar/postgresql/9.3.1/bin \\
  -B /usr/local/Cellar/postgresql/9.6.1/bin \\
  -d /usr/local/var/postgres9.3.1 \\
  -D /usr/local/var/postgres
cp /usr/local/Cellar/postgresql/9.6.1/homebrew.mxcl.postgresql.plist ~/Library/LaunchAgents/
launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

When you occasionally want to use PostgreSQL, you don’t want to get stuck on version updates.

Reference Information

• psqlしたらreadlineのエラーが出るようになって – はらいそ
• HomebrewでPostgresql9.1から9.3へアップデート - Qiita

That’s all from the Gemba.