Backup All PostgreSQL Databases with pg_dumpall

#!/usr/bin/env bash
#
# pg_backup.sh - Full cluster backup of all PostgreSQL databases and globals.
#
# pg_dumpall captures every database plus cluster-wide objects (roles,
# tablespaces). Output is compressed and timestamped.
#
# Usage: ./pg_backup.sh <output_dir> [pg_user]
#
# Authentication: relies on ~/.pgpass or peer auth. Never hard-code passwords.
#
set -euo pipefail

# --- Argument handling --------------------------------------------------------
if [[ $# -lt 1 || $# -gt 2 ]]; then
    echo "Usage: $0 <output_dir> [pg_user]" >&2
    exit 1
fi

OUT_DIR="$1"
PG_USER="${2:-postgres}"

command -v pg_dumpall >/dev/null 2>&1 || { echo "Error: pg_dumpall not found." >&2; exit 1; }
mkdir -p "$OUT_DIR"

TIMESTAMP="$(date +%Y%m%d-%H%M%S)"
OUTFILE="${OUT_DIR%/}/pg_cluster-${TIMESTAMP}.sql.gz"

# --- Dump the whole cluster ---------------------------------------------------
# -U sets the role; pg_dumpall includes roles and tablespaces by default.
echo "Backing up PostgreSQL cluster as user '$PG_USER' -> $OUTFILE"
pg_dumpall -U "$PG_USER" | gzip -c > "$OUTFILE"

echo "Done. Size: $(du -h "$OUTFILE" | cut -f1)"