[#65] status command

Implements the `status` command using `pg_ctl` as a way to check if the in-use instance is running or not.

Work implemented by @briansalehi revised by @theory and @fluca1978 .

Close #65

README.md

@@ -27,6 +27,9 @@ Synopsis
     # Start current version
     pgenv start
 
+    # Show server status
+    pgenv status
+
     # Restart current version
     pgenv restart
 
@@ -516,6 +519,32 @@ It is possible to specify flags to pass to `pg_ctl(1)` when performing the
 `restart` action, setting the `PGENV_RESTART_OPTIONS` array in the
 [configuration](#pgenv-config).
 
+### pgenv status
+
+Indicates whether an instance is already *running* or is *stopped*. In case an
+instance is not currently in use, the script complains and exits immediately.
+Furthermore, you can use `pgenv current` to see which version is in use.
+
+```sh
+$ pgenv status
+```
+
+The above command results in an output like the following:
+
+```
+server is running (PID: 81803)
+/opt/pgsql-16.0/bin/postgres "-D" "/opt/pgsql/data"
+```
+
+Same result can be achieved by running `pg_ctl` as follows:
+
+```sh
+$ $PG_ROOT/bin/pg_ctl status -D $PG_DATA
+```
+
+Where `PG_ROOT` is the path to your PostgreSQL installation directory, and
+`PG_DATA` is the path to your database directory.
+
 ### pgenv available
 
 Shows all the versions of PostgreSQL available to download and build. Handy to
@@ -601,6 +630,7 @@ The pgenv commands are:
     start      Start the current PostgreSQL server
     stop       Stop the current PostgreSQL server
     restart    Restart the current PostgreSQL server
+    status     Show the current PostgreSQL server status
     switch     Set the current PostgreSQL version
     clear      Stop and unset the current PostgreSQL version
     build      Build a specific version of PostgreSQL

bin/pgenv

@@ -146,6 +146,7 @@ The pgenv commands are:
     start      Start the current PostgreSQL server
     stop       Stop the current PostgreSQL server
     restart    Restart the current PostgreSQL server
+    status     Show the current PostgreSQL server status
     switch     Set the current PostgreSQL version
     clear      Stop and unset the current PostgreSQL version
     build      Build a specific version of PostgreSQL
@@ -915,7 +916,7 @@ pgenv_start_instance(){
     trap 'exit' ERR
 }
 
-# Initializes and instance if no data directory is found.
+# Initializes an instance if no data directory is found.
 # Requires PG_DATA to be set.
 # It is safe to call multiple times.
 pgenv_initdb(){
@@ -1168,6 +1169,15 @@ case $1 in
         exit
         ;;
 
+    status)
+        # only proceed when an instance is loaded
+        pgenv_exit_if_no_postgresql_in_use
+        # print standard postgres status
+        $PG_CTL status -s -D "$PG_DATA" | sed -E 's/^pg_ctl:\s+//'
+        # instance is either running or stopped at this point
+        exit $?
+        ;;
+
     build|rebuild)
         # load executables
         pgenv_check_dependencies