How do I specify which version of a program to run?

Question

Here's my situation: I have two versions of postgres installed, and with the two versions, come two different psql interactive terminals.

One is located at /usr/bin/psql, and starts when I run # psql -U username

Another newer one is located at /usr/pgsql-9.1/bin/psql

I want the newer one to start by default when I run psql from the command line. How can this be done? Thanks!

Edit: I am using centos

Answer 1

Edit your PATH so that /usr/pgsql-9.1/bin/ (the newer one) comes before /usr/bin/.

A less package-manager-safe safe alternative is to move/remove/rename the psql in /usr/bin/ and create a symlink in /usr/bin/ to the new one (not tested):

> cd /usr/bin
# move the old one however you like
> ln -s /usr/pgsql-9.1/bin/psql .

Answer 2

Alternatively, to avoid symlinks, and to avoid changing your $PATH, you could add your command to the hash table:

hash -p /usr/pgsql-9.1/bin/psql psql

This will put your command into the command hash table and it will be executed before any other command (in fact, no path search will be performed).

If you used a command called psql before, then it already sits in the hash table and it will be the first hit when searching for commands. In that case, remove the old entry first by typing

hash -d psql

and then issue the command above. You can source it in your .bashrc should you want to.