Agent-Skills.md

Agent Skills: psql — PostgreSQL Interactive Terminal

psql — PostgreSQL's interactive terminal client and SQL script runner (the `psql` command). Covers connection strings/URIs, `~/.pgpass` & service files, invocation flags (`-c`/`-f`/`-1`/`--csv`/`-qAtX`/`-v`), the `\d`-family inspection meta-commands, `\copy`, `\watch`, `\gexec`/`\gset`, `\if` scripting, `\pset` output formats & `\x`, variables & `:'…'` interpolation, `.psqlrc`, exit codes/`ON_ERROR_STOP`, and extended-protocol/pipeline commands (`\bind`/`\parse`/`\startpipeline`). Use when connecting to or inspecting a Postgres database from a terminal, running SQL scripts or one-off queries in shells/CI/agents, formatting or capturing query output, or fixing psql connection/auth problems. Includes inline (pgNN+) version annotations (pg14–pg19). This is the psql CLIENT only — for SQL syntax/data types use postgres-sql; for EXPLAIN/indexes/vacuum use postgres-performance; for server config/auth/backup/replication use postgres-admin; for CREATE EXTENSION use postgres-extensions.

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Skill Metadata

Name
psql
Description
psql — PostgreSQL's interactive terminal client and SQL script runner (the `psql` command). Covers connection strings/URIs, `~/.pgpass` & service files, invocation flags (`-c`/`-f`/`-1`/`--csv`/`-qAtX`/`-v`), the `\d`-family inspection meta-commands, `\copy`, `\watch`, `\gexec`/`\gset`, `\if` scripting, `\pset` output formats & `\x`, variables & `:'…'` interpolation, `.psqlrc`, exit codes/`ON_ERROR_STOP`, and extended-protocol/pipeline commands (`\bind`/`\parse`/`\startpipeline`). Use when connecting to or inspecting a Postgres database from a terminal, running SQL scripts or one-off queries in shells/CI/agents, formatting or capturing query output, or fixing psql connection/auth problems. Includes inline (pgNN+) version annotations (pg14–pg19). This is the psql CLIENT only — for SQL syntax/data types use postgres-sql; for EXPLAIN/indexes/vacuum use postgres-performance; for server config/auth/backup/replication use postgres-admin; for CREATE EXTENSION use postgres-extensions.

psql — PostgreSQL Interactive Terminal

Overview

psql is PostgreSQL's official command-line client: an interactive REPL and a SQL-script runner built on libpq. You use it to connect to a server, type SQL, inspect the schema with backslash meta-commands (\d, \dt, \df, …), format and capture output, and run scripts in shells, CI, and agents. It is a thin client — the database engine, SQL semantics, and server administration all live on the server, not in psql.

Key characteristics:

  • Client, not server — psql connects to a running PostgreSQL server; it stores no data and runs no SQL itself. Almost everything is gated by the psql (client) version, independent of the server you reach.
  • Two layers in one prompt — SQL (sent to the server, terminated by ;) and meta-commands (start with \, interpreted locally).
  • libpq under the hood — same connection strings/URIs, PG* environment variables, ~/.pgpass, and service files as every other PostgreSQL client.
  • Scriptable & pipeable — -c/-f/heredoc input, machine-readable output (--csv, -qAtX), meaningful exit codes, and ON_ERROR_STOP make it a first-class scripting tool.

Disambiguation — this is the psql client. This skill documents the psql program: its flags, connections, meta-commands, output formatting, variables, and scripting. It is not a SQL tutorial and does not cover server-side topics. For sibling concerns use: postgres-sql (SQL dialect, data types, DDL/DML), postgres-performance (EXPLAIN, indexes, VACUUM, planner), postgres-admin (postgresql.conf, roles/auth, backup, replication), postgres-extensions (CREATE EXTENSION, contrib modules). When in doubt: if it works the same in pgAdmin/DBeaver/a driver, it's not a psql topic — it belongs to a sibling skill.

When to Use This Skill

| Use psql when… | Prefer a sibling when… | |---|---| | Connecting to / inspecting a database from a terminal (\d, \l, \df) | Designing tables or writing queries → postgres-sql | | Running a SQL script or one-off query in a shell / CI / agent | Tuning a slow query, reading EXPLAIN → postgres-performance | | Formatting or capturing output (CSV, expanded, redirect to file) | Configuring the server, roles, backups → postgres-admin | | Debugging connection/auth (conninfo, .pgpass, services, SSL) | Installing/using an extension → postgres-extensions | | Writing .psqlrc, scripting with \set/\if/\gexec/\gset | Authoring the SQL those scripts run → postgres-sql |

Prerequisites & Version Note

psql --version        # e.g. "psql (PostgreSQL) 18.1"   (alias: psql -V)

This skill documents the psql surface as of the PostgreSQL 19beta1 source tree, so the latest stable line is pg18 and pg19 is beta. Long-standing features (present in pg13 and earlier) are bedrock and shown unannotated; features added later are tagged inline as (pgNN+), e.g. (pg16+). Two pre-14 classics are tagged anyway because scripts hit them on old clients: \gexec (pg9.6+) and the \if family (pg10+). Every tag is sourced — see references/version-features.md for the full feature→version map. Confirm what you're running with psql --version (client) and \echo :SERVER_VERSION_NUM (server).

psql ships with PostgreSQL (postgresql-client / postgresql packages, or brew install libpq). A newer psql talks to older servers fine and vice-versa.

The psql CLI at a Glance

These invocations cover ~90% of usage:

psql                                   # connect using PG* env vars / defaults, interactive REPL
psql -d "postgresql://user@host/mydb"  # connect via a URI (or conninfo string)
psql -h db -U me -d app                # connect via discrete flags
psql -c "SELECT version()"             # run one command and exit (great for scripts)
psql -f script.sql                     # run a SQL file and exit
psql -qAtX -c "SELECT count(*) FROM t" # quiet, unaligned, tuples-only, no .psqlrc → clean scalar
psql --csv -c "SELECT * FROM t"        # CSV output (safe quoting) for parsing

Usage: psql [OPTION]... [DBNAME [USERNAME]]. The first non-option argument is the database (or a full conninfo/URI); a second is the username.

Most useful flags (full list in references/scripting.md & references/connection.md):

| Flag | Meaning | |------|---------| | -c CMD | Run one SQL string or one backslash command, then exit (repeatable; combine with -f) | | -f FILE | Run a SQL file then exit (gives line-numbered errors) | | -1 / --single-transaction | Wrap all -c/-f work in one BEGIN/COMMIT (all-or-nothing) | | -X / --no-psqlrc | Skip ~/.psqlrc — always use in scripts for reproducibility | | -q / -A / -t | Quiet / unaligned / tuples-only (combine as -qAt for clean parsing) | | --csv | CSV output mode (= \pset format csv) | | -F SEP / -R SEP / -z / -0 | Field / record separators; -z/-0 use NUL (for xargs -0) | | -v NAME=VAL | Set a psql variable (e.g. -v ON_ERROR_STOP=1) | | -o FILE / -L FILE | Send query output to a file / log all output to a file too | | -x | Expanded output (one column per line) | | -E | Echo the hidden catalog query behind each \d command | | -h/-p/-U/-d · -w/-W | Host / port / user / dbname · never-prompt / force-prompt for password |

Output formats (\pset format X or a flag): aligned (default), unaligned, csv, wrapped, html, asciidoc, latex, latex-longtable, troff-ms. Toggle expanded rows with \x.

Connecting

Four interchangeable mechanisms (mix freely; conninfo > flags > env > service > defaults):

psql -h db.example.com -p 5432 -U me -d app          # discrete flags
psql "host=db user=me dbname=app sslmode=require"    # conninfo string
psql postgresql://me@db.example.com:5432/app         # URI
PGHOST=db PGUSER=me PGDATABASE=app psql              # environment variables
psql service=prod                                    # a ~/.pg_service.conf entry
  • No password on the command line (it leaks via ps). Use ~/.pgpass (lines of host:port:db:user:password, chmod 0600), the PGPASSWORD env var, or an interactive prompt.
  • ~/.pg_service.conf names a bundle of parameters: connect with service=NAME.
  • \c [conninfo] reconnects mid-session; \conninfo shows the current connection.
  • For TLS use sslmode=verify-full; for HA list comma-separated hosts + target_session_attrs=read-write.

Full reference (flags, .pgpass, service files, SSL, multi-host, precedence): references/connection.md.

Core Workflows

1. Inspect the schema (the \d family)

\l                      -- list databases
\dt                     -- list tables (\dv views, \di indexes, \dm matviews, \ds sequences)
\d orders               -- one relation: columns, types, indexes, constraints, triggers
\d+ orders              -- + storage, replica identity, access method, comments
\df pg_catalog.now      -- functions; \sf func shows the CREATE OR REPLACE source
\dn                     -- schemas;  \dx  installed extensions;  \du / \drg (pg16+) roles/grants
\dconfig work_mem       -- server config parameters (pattern-aware SHOW)        (pg15+)

Suffixes: S includes system objects, + adds detail, and in pg18+ a trailing x on a listing command forces expanded output (\dt+x). Add -E (or \set ECHO_HIDDEN on) to see the catalog query a \d command runs — a great way to learn the catalogs. Full catalog: references/meta-commands.md.

2. Format & capture output

\x on                            -- expanded: one column per line (wide rows)
\pset null '(null)'              -- show NULLs visibly
\pset format csv                 -- CSV for the session (or --csv on the CLI)
\timing on                       -- print how long each statement takes
\o results.txt                   -- send subsequent output to a file (\o alone reverts)
SELECT * FROM big \g out.csv     -- one-shot: send THIS query's output to a file
SELECT * FROM big \g |less       -- one-shot: pipe THIS query's output to a command

3. Variables & interpolation

\set tbl orders
SELECT count(*) FROM :"tbl";                      -- :"x" = quoted identifier
\set cutoff '2026-01-01'
SELECT * FROM orders WHERE created >= :'cutoff';  -- :'x' = quoted literal (injection-safe)
SELECT count(*) AS n FROM orders \gset            -- store result columns into variables
\echo there are :n orders
\getenv home HOME                                 -- env var → psql variable               (pg15+)

Use :'var' / :"var" for any untrusted value; raw :var is unquoted (injection risk). For true server-side parameter binding, see \bind (references/pipeline.md).

4. Power tools

-- \gexec (pg9.6+): run query, then execute each result cell as SQL — metaprogramming
SELECT format('ANALYZE %I;', tablename) FROM pg_tables WHERE schemaname='public' \gexec

-- \watch: re-run on an interval (count= & named forms pg16+, min_rows= pg17+)
SELECT count(*) FROM jobs WHERE state='running' \watch interval=5 count=12

-- \crosstabview (pg9.6+): pivot a 3-column result into a grid
SELECT category, region, sum(amt) FROM sales GROUP BY 1,2 \crosstabview

-- \if family (pg10+): branch in scripts (pair with \gset)
SELECT EXISTS(SELECT 1 FROM pg_roles WHERE rolname='deploy') AS ok \gset
\if :ok
    \echo role present
\else
    CREATE ROLE deploy LOGIN;
\endif

5. Client-side \copy (no server file access)

\copy (SELECT * FROM orders WHERE created > now() - interval '1 day') TO 'recent.csv' WITH (FORMAT csv, HEADER)
\copy customers (id, name, email) FROM 'customers.csv' WITH (FORMAT csv, HEADER)

\copy streams the file through the client, so it uses your local paths/permissions — no server superuser or pg_read_server_files needed (unlike SQL COPY).

Non-Interactive / Agent Usage

Prefer one-shot, machine-readable invocations over the REPL. The canonical agent/CI pattern:

# Clean scalar: quiet, unaligned, tuples-only, ignore ~/.psqlrc
psql -qAtX -c "SELECT count(*) FROM orders"

# Structured output — CSV handles embedded commas/quotes/newlines safely
psql -X --csv -c "SELECT id, email FROM users WHERE active" > users.csv

# Fail fast with a detectable exit code (3) on any SQL error
psql -X -v ON_ERROR_STOP=1 -f migrate.sql

# All-or-nothing migration (single transaction, rolls back on error)
psql -X -1 -v ON_ERROR_STOP=1 -f migration.sql

# Multi-statement / mixed SQL + meta-commands via heredoc
psql -X <<'SQL'
\timing on
INSERT INTO t SELECT * FROM staging;
SELECT count(*) FROM t;
SQL

# Pass values safely as quoted literals/identifiers
psql -X -v tbl=orders -v d='2026-01-01' \
  -c "SELECT count(*) FROM :\"tbl\" WHERE created >= :'d'"

Exit codes: 0 ok · 1 fatal psql error (bad option, file not found) · 2 connection failed/lost (non-interactive) · 3 SQL error with ON_ERROR_STOP set. So ON_ERROR_STOP=1 is what turns a failed statement into a non-zero exit.

Agent tips: always pass -X (ignore ~/.psqlrc); use -qAt or --csv for parseable output; set ON_ERROR_STOP=1; use -1 for atomic multi-statement scripts; pass external values via -v + :'…'/:"…" (never string-concatenate); set FETCH_COUNT for huge result sets to bound memory. Full guide: references/scripting.md.

Extended Protocol & Pipelines

By default psql uses the simple query protocol. A small family drives the extended protocol for safe parameter binding and request pipelining:

SELECT $1::int + $2::int \bind 3 4 \g          -- bind params, extended protocol      (pg16+)
SELECT $1 \parse stmt1                          -- named prepared statement            (pg18+)
\bind_named stmt1 'value' \g                    --   execute it with parameters        (pg18+)

\bind (pg16+) is the safest way to pass parameters from psql. The named-statement and pipeline commands (\startpipeline/\sendpipeline/\endpipeline/\getresults/…) are pg18+ — they were absent from pg16 and pg17. Details and the full command list: references/pipeline.md.

Quick Reference

| Item | Purpose | |------|---------| | psql -c "SQL" / psql -f f.sql | Run one command / a file, then exit | | psql -qAtX -c "SQL" | Quiet, unaligned, tuples-only, no .psqlrc — clean script output | | psql --csv -c "SQL" | CSV output (RFC-4180 quoting) for parsing | | psql -X -1 -v ON_ERROR_STOP=1 -f m.sql | Atomic, fail-fast migration | | \d · \dt · \d+ t · \df · \dn · \dx · \l | Inspect: relation / tables / detail / functions / schemas / extensions / databases | | \dconfig (pg15+) · \drg (pg16+) · \dX (pg14+) | Server config / role grants / extended stats | | \g [file\|\|cmd] · \gx · \o file | Send query (redirect) / expanded / persistent output redirect | | \gexec (pg9.6+) · \gset · \gdesc (pg11+) | Run results as SQL / capture into vars / describe columns | | \watch [i=][c=][m=] · \crosstabview (pg9.6+) | Re-run on interval / pivot to a grid | | \if/\elif/\else/\endif (pg10+) | Script conditionals (pair with \gset) | | \set · :var / :'var' / :"var" | Variables / raw / quoted-literal / quoted-identifier interpolation | | \pset format csv\|unaligned · \x · \t · \a · \timing | Output mode / expanded / tuples-only / align toggle / timings | | \copy … FROM\|TO 'file' (FORMAT csv, HEADER) | Client-side import/export (local file perms) | | \c [conninfo] · \conninfo · \password | Reconnect / show connection / change password safely | | \bind (pg16+) · \parse/\bind_named/pipelines (pg18+) | Extended-protocol & pipeline commands | | \? · \h SQL · \q | Backslash help / SQL syntax help / quit | | ~/.pgpass · ~/.pg_service.conf · ~/.psqlrc | Password file / connection services / startup script |

Troubleshooting

  • psql: command not found — install the client (postgresql-client, or brew install libpq and add it to PATH); it's separate from the server.
  • could not connect to server / Connection refused — wrong host/port, server down, or pg_hba.conf/firewall. Check -h/-p, that the server listens, and try psql -h localhost vs the socket. (pg_hba.conf and listen_addresses are postgres-admin topics.)
  • fe_sendauth: no password supplied — add a ~/.pgpass entry (chmod 0600), set PGPASSWORD, or pass -W to prompt. A wrong-permissions .pgpass is silently ignored.
  • -c won't mix SQL and a backslash command — one -c is either SQL or one meta-command. Use repeated -c, a heredoc, or -f.
  • A newer meta-command errors (invalid command \…) — your client is too old. Check psql --version and references/version-features.md. E.g. pipelines/\parse/\close_prepared are pg18+, \getenv/\dconfig pg15+, \bind pg16+.
  • \restrict errors when restoring a dump — the dump was made by a newer pg_dump; restore with a psql at least as new (the 2025-08 security backport, see version-features.md).
  • Script keeps going after an error — set ON_ERROR_STOP=1 (default is to continue). Wrap with -1 for atomicity.
  • Output is misaligned/garbled in a pipe — the pager or alignment is interfering; use -qAt or --csv, and -X to ignore a personal ~/.psqlrc.
  • \d shows less/more than expected — server-version dependent; some columns only appear when the server is new enough, regardless of client version.

References

For exhaustive detail, see the bundled reference files:

  • references/meta-commands.md — every backslash command, grouped: the \d inspection family, query execution (\g/\gexec/\gset/\watch/\crosstabview), formatting (\pset/\x), variables, conditionals, \copy, connection & system commands, with inline (pgNN+) tags.
  • references/connection.md — conninfo strings & URIs, all PG* environment variables, ~/.pgpass, connection service files, SSL/multi-host, \c, and precedence rules.
  • references/scripting.md — non-interactive/agent patterns, ON_ERROR_STOP/exit codes, transactions (-1/AUTOCOMMIT/ON_ERROR_ROLLBACK), the special control variables, interpolation, FETCH_COUNT streaming, .psqlrc, and psql environment vars.
  • references/pipeline.md — the extended-protocol & pipeline meta-commands (\bind, \parse, \bind_named, \close_prepared, \startpipeline/…), with the pg16/pg18 version story.
  • references/version-features.md — feature → minimum-version map with postgresql.org sources (what's bedrock vs. added in pg14–pg19, plus the \restrict backport).

Resources

  • Help: psql --help, \? (meta-commands), \? variables, \h (SQL syntax)
  • psql reference: https://www.postgresql.org/docs/current/app-psql.html
  • libpq connection strings: https://www.postgresql.org/docs/current/libpq-connect.html
  • Release notes (per-version feature history): https://www.postgresql.org/docs/release/