Add brew shellenv - see #4780

[jamescostian]

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---

Adds brew shellenv based on conversation in #4780

[MikeMcQuaid]

Looks good to me, thanks @jamescostian and sorry for all the back and forth! Is this sufficient for your use-case @sjackman? If so, mind ✅

[MikeMcQuaid]

Could you assert_match on e.g. the HOMEBREW_PREFIX/bin being present?

[sjackman]

Looks good to me. Thanks, James! The one minor test change suggested by make would be good, to check that stdout contains #{HOMEBREW_PREFIX}/bin.

[sjackman]

After this is merge into Homebrew/brew and Linuxbrew/brew, we can update the installation instructions.

[jamescostian]

Just added that to the test 👍

[sjackman]

Merged. Thanks for your contribution to Homebrew, James! 🏆

[sjackman]

There's two ways that brew shellenv could be added to ~/.profile.

~/.linuxbrew/bin/brew shellenv >>~/.profile

or

echo 'eval $(~/.linuxbrew/bin/brew shellenv)' >>~/.profile

I have a slight preference for the latter using eval. Your opinion?

[jamescostian]

Running time bin/brew shellenv on my laptop (processor is i7-4870HQ, running at 2.8GHz, mostly idling) reports a real time of 0.40s, which IMO makes it way too slow for me to be willing to eval it more than once

[sjackman]

Agreed. It's 0.9s in my Docker instance. ⏱

[sjackman]

So the installation instructions should be…

eval $(~/.linuxbrew/bin/brew shellenv)
brew shellenv >>~/.profile

[MikeMcQuaid]

@sjackman My recommendation would be to advise people put eval in their profile and those who care about the overhead can hardcode it if necessary.

Another possible extension for this script would be exporting e.g. HOMEBREW_PREFIX and HOMEBREW_CELLAR so scripts (or the profile itself) can avoid calling brew --prefix to further improve performance.

Nice work @jamescostian!

[sjackman]

My recommendation would be to advise people put eval in their profile and those who care about the overhead can hardcode it if necessary.

Is that so that we can change the output of brew shellenv, and have all users up-to-date without needing to modify their shell configuration?

I suspect that implementing this script in shell rather than Ruby would execute quite a bit faster. If it's going in ~/.profile maybe it's not such a big deal, since it'd only be executed when opening a new terminal (or ssh session). I'd be more concerned if it's going in ~/.bashrc where it'd be executed for every subshell.

[MikeMcQuaid]

Is that so that we can change the output of brew shellenv, and have all users up-to-date without needing to modify their shell configuration?

Yep 👍

I suspect that implementing this script in shell rather than Ruby would execute quite a bit faster

It would indeed. Given it only relies on HOMEBREW_PREFIX being defined and even any extensions I see would only need things already defined in the Bash layer it should be possible to rewrite it in Bash, name it cmd/shellenv.sh and it'll avoid needing to ever execute the Ruby layer.

[sjackman]

@jamescostian Would you be interested in submitting a PR to rewrite shellenv in shell so that it takes less time to execute?

[jamescostian]

Sure, the bash rewrite is pretty simple:

echo "export PATH=\"$HOMEBREW_PREFIX/bin:$HOMEBREW_PREFIX/sbin:\$PATH\""
echo "export MANPATH=\"$HOMEBREW_PREFIX/share/man:\$MANPATH\""
echo "export INFOPATH=\"$HOMEBREW_PREFIX/share/info:\$INFOPATH\""
echo "export HOMEBREW_PREFIX=\"$HOMEBREW_PREFIX\""

But there are two issues:

1. I'm getting an error at the end of the output: "Library/Homebrew/brew.sh: line 405: homebrew-shellenv: command not found" - any tips for that?
2. Even if I comment out the line that makes that error, the execution time is .10s

That execution time seems to be impacted most from this line and this line. They both talk to git and they both look important enough to keep.

One way to decrease the execution time to .01s would be to treat shellenv completely differently: see the next comment for a better way

--- a/bin/brew
+++ b/bin/brew
@@ -65,7 +65,7 @@ do
 done

 # test-bot does environment filtering itself
-if [[ -z "$HOMEBREW_NO_ENV_FILTERING" && "$1" != "test-bot" ]]
+if [[ -z "$HOMEBREW_NO_ENV_FILTERING" && "$1" != "test-bot" && "$1" != "shellenv" ]]
 then
   PATH="/usr/bin:/bin:/usr/sbin:/sbin"

@@ -82,6 +82,11 @@ then
   done

   exec /usr/bin/env -i "${FILTERED_ENV[@]}" /bin/bash "$HOMEBREW_LIBRARY/Homebrew/brew.sh" "$@"
+elif [[ "$1" == "shellenv" ]]
+then
+  echo "export PATH=\"$HOMEBREW_PREFIX/bin:$HOMEBREW_PREFIX/sbin:\$PATH\""
+  echo "export MANPATH=\"$HOMEBREW_PREFIX/share/man:\$MANPATH\""
+  echo "export INFOPATH=\"$HOMEBREW_PREFIX/share/info:\$INFOPATH\""
+  echo "export HOMEBREW_PREFIX=\"$HOMEBREW_PREFIX\""
 else
   source "$HOMEBREW_LIBRARY/Homebrew/brew.sh"
 fi

[jamescostian]

Update: here's a much less ugly approach (or at least, it's already been used elsewhere in the code):

--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -17,6 +17,10 @@ case "$*" in
   --prefix)            echo "$HOMEBREW_PREFIX"; exit 0 ;;
   --cellar)            echo "$HOMEBREW_CELLAR"; exit 0 ;;
   --repository|--repo) echo "$HOMEBREW_REPOSITORY"; exit 0 ;;
+  shellenv)            echo "export PATH=\"$HOMEBREW_PREFIX/bin:$HOMEBREW_PREFIX/sbin:\$PATH\"";
+                       echo "export MANPATH=\"$HOMEBREW_PREFIX/share/man:\$MANPATH\"";
+                       echo "export INFOPATH=\"$HOMEBREW_PREFIX/share/info:\$INFOPATH\"";
+                       echo "export HOMEBREW_PREFIX=\"$HOMEBREW_PREFIX\"";
+                       exit 0 ;;
 esac

 # A depth of 1 means this command was directly invoked by a user.

This approach also brings the time down to .01s

[sjackman]

I have a mild preference for the following style over using backslashes to escape.

echo "export PATH='$HOMEBREW_PREFIX/bin:$HOMEBREW_PREFIX/sbin'":'"$PATH"'

I'll defer to Mike on your question regarding speed.

[MikeMcQuaid]

I'm getting an error at the end of the output: "Library/Homebrew/brew.sh: line 405: homebrew-shellenv: command not found" - any tips for that?

You need to put your code inside a function homebrew-shellenv() { .. }.

On my machine there's still a 3.5x speedup by moving this from Ruby to shell (0.72s to 0.21s). I'm not convinced it's worth making the brew.sh code less maintainable to put this directly in brew.sh (imagine if we want to extend brew shellenv in future or even just keep having the --help work).