Return to readline version 6.x in Homebrew to fix Postgresql?

Question

I'm no Homebrew expert but I think it has "upgraded" me from readline version 6.x to 7.0 sometime after 9/15/16:

eat@eric-macbook:Homebrew$ brew info readline readline: stable 7.0 (bottled) [keg-only] Library for command-line editing https://tiswww.case.edu/php/chet/readline/rltop.html /usr/local/Cellar/readline/7.0 (45 files, 2M) 

This has caused headaches for my 9.4.5 Homebrew version of Postgresql (I need the older 9.4 for comparability reasons):

eat@eric-macbook:~$ psql --version dyld: Library not loaded: /usr/local/opt/readline/lib/libreadline.6.dylib   Referenced from: /usr/local/Cellar/postgresql/9.4.5/bin/psql   Reason: image not found Trace/BPT trap: 5 

Unfortunately I can't find a 6.x version of readline on Homebrew to revert to - only 7.0 seems to be available(?).

My question is twofold:

• Is the the readline version mismatch the cause of my postgres/psql problem?
• If so, how do I return to 6.x with Homebrew to correct the problem?

Thank you in advance!

Answer 1

To answer the specific question.

You can switch between version of installed brew packages which are still around locally as explained in this question: Homebrew install specific version of formula?

To downgrade to readline 6.x the following command worked for me:

brew switch readline 6.3.8