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Fixing a Slow Bash Prompt

Posted on Mon 01 February 2021 in Posts

I recently got a new machine for my new job, and so I'm going through all the "new machine setup" gotchas. Since getting it, I've been finding the shell/terminal has felt really sluggish. Like I’d hit enter in a terminal and it’d be 1-2 seconds before the prompt came back allowing me to type anything again, which makes someone who likes to type a lot of commands in quick succession get angry. 😠

After a bunch of troubleshooting & reverse engineering I found it came down to the __git_ps1 function that displays your current branch in your bash prompt. How slow was it? Really slow:

 λ time __git_ps1
 (mainline)
real    0m1.746s
user    0m0.044s
sys 0m0.079s

That’s 1.7 seconds every time I hit enter in a terminal because it gets evaluated as part of producing my bash prompt.

I thought this was weird, so I did a git --version and noticed that I was running git version 2.24.3 (Apple Git-128). That is the special “Apple has built this version for you and installed as part of Xcode command-line tools” version.

So, I installed git from Homebrew (brew install git), which gave be the same normal version that anyone on any platform would get (just compiled for OSX), and also gave me a much newer version (2.30.0). Much faster. How much faster? Check it out:

 λ time __git_ps1
 (mainline)
real    0m0.060s
user    0m0.016s
sys 0m0.026s

From 1.7 seconds to 0.06 seconds. Crazy. Now my command prompt is nice and snappy.