postgresql-cli – skill Viết lách & Nội dung cho agent AI

psql — PostgreSQL Interactive Terminal

psql is PostgreSQL's feature-rich interactive terminal. It lets you write and execute queries, inspect database objects, import/export data, script batch operations, and customize output formatting — all from the command line.

Execution boundary

Confirm the authorized database, role and operation scope before writes, imports, grants or shell commands. Prefer a least-privileged account, -X -v ON_ERROR_STOP=1 for reviewed scripts and verified TLS (sslmode=verify-full with trusted CA) for remote connections. ECHO is not a dry-run and rollback cannot undo every side effect. This reference includes psql 18 features; check client version separately from server version.

Prerequisites

Before using psql, verify it is installed and available:

# Check if psql is installed
psql --version
# If not found, install PostgreSQL client tools:
# macOS (Homebrew)
brew install libpq
# Add the installed libpq bin directory to PATH; avoid force-linking over other PostgreSQL tools.
# Ubuntu / Debian
sudo apt install postgresql-client
# CentOS / RHEL
sudo yum install postgresql
# Alpine
apk add postgresql-client

# Windows — install PostgreSQL via the official installer or use WSL

psql ships as part of the postgresql-client package. The server (postgresql) is not required — you only need the client to connect to a remote PostgreSQL instance.

Quick Reference

Connecting

# 1. CLI flags
psql -h host -p port -U user -d dbname

# 2. Connection URI
# WARNING: Password in URI is visible in shell history and process listings.
#          Prefer ~/.pgpass for production use (see method 4 below).
psql "postgresql://user:YOUR_PASSWORD@host:port/dbname"

# 3. Environment variables (no flags needed)
export PGHOST=localhost
export PGPORT=5432
export PGDATABASE=mydb
export PGUSER=postgres
# WARNING: PGPASSWORD is visible in process listings (e.g. `ps aux`).
#          Use ~/.pgpass in production instead.
export PGPASSWORD=YOUR_PASSWORD
psql                       # picks up all params from env

# 4. ~/.pgpass file (RECOMMENDED for passwords)
#    Format: hostname:port:database:username:password
touch ~/.pgpass && chmod 600 ~/.pgpass
# Then manually edit ~/.pgpass and add entries (avoids password in shell history):
# hostname:port:database:username:password
# Example: localhost:5432:mydb:postgres:YOUR_PASSWORD
psql -h localhost -U postgres -d mydb   # no password prompt

# 5. Execute and exit
psql -f script.sql dbname                        # execute file then exit
psql -c "SELECT 1" dbname                        # run single command then exit
psql -X -v ON_ERROR_STOP=1 -1 -f migration.sql dbname                  # run in single transaction

# 6. Service connection (reads from pg_service.conf)
psql service=mydb_prod

# 7. Reconnect within a session
\c dbname                                       # reconnect to different db
\c -reuse-previous=on sslmode=require           # change only sslmode
\c "host=newhost port=5432 dbname=mydb"         # conninfo string

On connection failure: interactive mode keeps the previous connection; script mode closes it and all subsequent database commands fail until the next successful \c.

Key flags: -h host, -p port, -U user, -d database, -w no password prompt, -W force password prompt, -1 single transaction, -f execute file, -c execute command, -t tuples only, -x expanded, -A unaligned, -E echo hidden queries (\d internals), -L log file, -X skip ~/.psqlrc.

Connection precedence: CLI flags > environment variables > pg_service.conf > defaults. Password precedence: connection string/password flag > PGPASSWORD env > ~/.pgpass. Use ~/.pgpass instead of PGPASSWORD in production — PGPASSWORD is visible in process listings (ps aux).

Object Inspection (\d family)

| Command | Shows |

| ----------------- | ----------------------------------------------------------------------------------------------------- |

| \d | All tables, views, materialized views, sequences, foreign tables (equiv.\dtvmsE) |

| \dP | Partitioned tables |

| \dt | Tables only |

| \dv | Views only |

| \di | Indexes only |

| \ds | Sequences only |

| \dm | Materialized views only |

| \det | Foreign tables (mnemonic: "external tables") |

| \dT | Data types |

| \df | Functions (use modifiers:a=aggregate, n=normal, p=procedure, t=trigger, w=window) |

| \da | Aggregate functions |

| \dn | Schemas |

| \du / \dg | Roles |

| \db | Tablespaces |

| \dc | Conversions |

| \dD | Domains |

| \dl | Large objects (alias for \lo_list) |

| \dF | Text search configurations |

| \dFd | Text search dictionaries |

| \dFp | Text search parsers |

| \dFt | Text search templates |

| \des | Foreign servers |

| \deu | User mappings |

| \dew | Foreign-data wrappers |

| \dp | Privileges (GRANT/REVOKE) |

| \drds | Per-role and per-database configuration settings |

| \l | List databases (accepts pattern:\l test*) |

| \dA | Access methods |

| \dAc / \dAf / \dAo / \dAp | Operator classes, families, operators, support functions |

| \dC | Type casts |

| \dconfig | Server configuration parameters (\dconfig * for all, PostgreSQL 16+) |

| \dd | Object descriptions (comments) |

| \ddp | Default privileges |

| \dL | Procedural languages |

| \do | Operators (accepts arg type patterns) |

| \dO | Collations |

| \dP[itn] | Partitioned tables (t=tables, i=indexes, n=nested) |

| \drg | Granted role memberships |

| \dRp / \dRs | Replication publications / subscriptions |

| \dX | Extended statistics |

| \dx | Installed extensions |

| \dy | Event triggers |

| \sf[+] | Show function definition |

| \sv[+] | Show view definition |

| \z | Privileges (alias for \dp) |

Modifiers (append to most \d commands):

• + — extra info (size, description): \dt+,

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