Speeding up zsh

Something that had been irking me for a while was how long Zsh took to load.

“How long” was subjective until I finally decided to profile it.

time zsh -i -c exit

It took nearly 30 seconds to start Zsh — yikes.

What made it even stranger was that I wasn’t using Oh My Zsh with dozens of plugins loaded.

So I set out to fix it.

The first step was figuring out what was slowing startup down. Zsh has a built-in profiler called zprof, which made this surprisingly easy.

# Add to beggining of zshrc
zmodload zsh/zprof
...
# add to the end of zshrc
zprof

It took nearly 30 seconds to start Zsh — yikes.

What made it even stranger was that I wasn’t using Oh My Zsh with dozens of plugins loaded.

So I set out to fix it.

The first step was figuring out what was slowing startup down. Zsh has a built-in profiler called zprof, which made this surprisingly easy.

#before
[ -s "/opt/homebrew/opt/nvm/nvm.sh" ] && \. "/opt/homebrew/opt/nvm/nvm.sh"  # This loads nvm
[ -s "/opt/homebrew/opt/nvm/etc/bash_completion.d/nvm" ] && \. "/opt/homebrew/opt/nvm/etc/bash_completion.d/nvm"  # This loads nvm bash_completion

eval "$(pyenv init -)"

conda init --all
#after
nvm() {
  unset -f nvm node npm npx
  source "$NVM_DIR/nvm.sh"
  nvm "$@"
}

node() { nvm; node "$@"; }
npm()  { nvm; npm "$@"; }
npx()  { nvm; npx "$@"; }

pyenv() {
  unset -f pyenv
  export PYENV_ROOT="$HOME/.pyenv"
  export PATH="$PYENV_ROOT/bin:$PATH"
  eval "$(command pyenv init -)"
  pyenv "$@"
}

conda() {
  unset -f conda
  source /opt/miniconda3/etc/profile.d/conda.sh
  conda "$@"
}

This alone significantly reduced startup time.

I was also able to shave off a couple more seconds by optimizing Zsh completions.

# Before 
compinit

#After
compinit -C -u #which skips building the .zcompdump

# Instead use cache 
mkdir -p ~/.zsh/cache 
zstyle ':completion:*' use-cache true 
zstyle ':completion:*' cache-path ~/.zsh/cache

A shell that previously took ~30 seconds to start now feels nearly instant.