git/list[1] front-page[2] threads[3] people[4] search[5] about
 

Re: [PATCH 19/19] bash prompt: alternative git prompt without command substitution

From
ASAndrew Sayers <andrew-git@pileofstuff.org>
Date
May 9, 2012, 19:38 UTC
Message-ID
<4FAAC7AE.3020002@pileofstuff.org>
In-Reply-To
<1336524290-30023-20-git-send-email-szeder@ira.uka.de>
On 09/05/12 01:44, SZEDER Gábor wrote:
Show 22 quoted lines
> __git_ps1() prints the branch name, status indicators, etc. to stdout,
> therefore it has to be included in $PS1 through a command substitution
> to display that information in the prompt.  The configuration is
> straightforward, but it imposes the overhead of fork()ing a subshell
> for the command substitution.
> 
> However, bash has the $PROMPT_COMMAND shell variable, which "if set,
> the value is executed as a command prior to issuing each primary
> prompt" (quoted from bash man page).  Its value isn't executed in a
> subshell but in the context of the "main" shell, hence (non-local)
> variables set in invoked shell functions are available when expanding
> $PS1.  We can use this facility to avoid that command substitution for
> __git_ps1().
> 
> So split out the meat of __git_ps1() into the new
> __git_prompt_command() function, which stores the branch name & co.
> in the $__git_ps1_string variable.  This function, as its name
> suggests, should be included in $PROMPT_COMMAND, and $__git_ps1_string
> should in turn be included in $PS1 with a bit of a twist to put the
> parentheses around it:
> 
>    PROMPT_COMMAND=__git_prompt_command

Rather than overwrite any existing PROMPT_COMMAND, it would be better to do something like:

PROMPT_COMMAND="__git_prompt_command; $PROMPT_COMMAND"
Show 117 quoted lines
>    PS1='[\u@\h \W${__git_ps1_string:+ ($__git_ps1_string)}]\$ '
> 
> Turn __git_ps1() into a wrapper around __git_prompt_command() such
> that it's functionality remains unaltered, so already configured
> prompts won't break.
> 
> The whole series speeds up the bash prompt on Windows/MinGW
> immensely, in many cases brings it down to around 10ms on my
> machine while in powersave mode.  Here are some timing results in
> three common scenarios (repeated 10 times, because the after cases
> were too fast to measure a single execution accurately with 'time'):
> 
> In my home directory, i.e. not in a git repository, before:
> 
>     /c/Users/szeder
>     $ time for i in {0..9} ; do prompt=$(__git_ps1) ; done
> 
>     real    0m0.952s
>     user    0m0.214s
>     sys     0m0.444s
> 
>   After:
> 
>     /c/Users/szeder
>     $ time for i in {0..9} ; do __git_prompt_command ;
>            prompt=${__git_ps1_string:+ ($__git_ps1_string)} ; done
> 
>     real    0m0.718s
>     user    0m0.136s
>     sys     0m0.354s
> 
>   After, with discovery across filesystems enabled:
> 
>     /c/Users/szeder
>     $ time for i in {0..9} ; do __git_prompt_command ;
>            prompt=${__git_ps1_string:+ ($__git_ps1_string)} ; done
> 
>     real    0m0.078s
>     user    0m0.016s
>     sys     0m0.062s
> 
> At the top of a work tree, before:
> 
>     /c/Users/szeder/repo (master)
>     $ time for i in {0..9} ; do prompt=$(__git_ps1) ; done
> 
>     real    0m2.901s
>     user    0m0.391s
>     sys     0m1.468s
> 
>   After:
> 
>     /c/Users/szeder/repo (master)
>     $ time for i in {0..9} ; do __git_prompt_command ;
>            prompt=${__git_ps1_string:+ ($__git_ps1_string)} ; done
> 
>     real    0m0.094s
>     user    0m0.047s
>     sys     0m0.047s
> 
> In a subdirectory, stash indicator enabled, before:
> 
>     /c/Users/szeder/repo/subdir (master $)
>     $ time for i in {0..9} ; do prompt=$(__git_ps1) ; done
> 
>     real    0m4.118s
>     user    0m0.468s
>     sys     0m2.056s
> 
>   After:
> 
>     /c/Users/szeder/repo/subdir (master $)
>     $ time for i in {0..9} ; do __git_prompt_command ;
>            prompt=${__git_ps1_string:+ ($__git_ps1_string)} ; done
> 
>     real    0m0.858s
>     user    0m0.152s
>     sys     0m0.322s
> 
>   After, discovery across filesystems enabled:
> 
>     /c/Users/szeder/repo/subdir (master $)
>     $ time for i in {0..9} ; do __git_prompt_command ;
>            prompt=${__git_ps1_string:+ ($__git_ps1_string)} ; done
> 
>     real    0m0.109s
>     user    0m0.047s
>     sys     0m0.063s
> 
> Well, that's about 97% improvement.
> 
> The performance gain on Linux is smaller, the latter case goes down
> from 0.264s to 0.047, but since it was fast enough to begin with I
> won't lengthen this commit message with further timing results on
> Linux.
> 
> Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
> ---
> 
> We had some discussions recently about putting user-facing functions into
> a separate "namespace".  This patch doesn't take that into account, but
> once a consensus is reached __git_prompt_command() should be put in that
> namespace.
> 
>  contrib/completion/git-completion.bash | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
> index 5ea19018..1c29f3d0 100755
> --- a/contrib/completion/git-completion.bash
> +++ b/contrib/completion/git-completion.bash
> @@ -29,6 +29,11 @@
>  #       are currently in a git repository.  The %s token will be
>  #       the name of the current branch.
>  #
> +#       Alternatively, to make the above Bash prompt a bit faster:
> +#               PROMPT_COMMAND=__git_prompt_command

As above, I'd recommend a simple documentation change: PROMPT_COMMAND="__git_prompt_command; $PROMPT_COMMAND" (to show people how to chain any other prompt commands they have)

Show 39 quoted lines
> +#               PS1='[\u@\h \W${__git_ps1_string:+ ($__git_ps1_string)}]\$ '
> +#               GIT_DISCOVERY_ACROSS_FILESYSTEM=true
> +#
>  #       In addition, if you set GIT_PS1_SHOWDIRTYSTATE to a nonempty
>  #       value, unstaged (*) and staged (+) changes will be shown next
>  #       to the branch name.  You can configure this per-repository
> @@ -258,11 +263,12 @@ __git_ps1_show_upstream ()
>  }
>  
>  
> -# __git_ps1 accepts 0 or 1 arguments (i.e., format string)
> -# returns text to add to bash PS1 prompt (includes branch name)
> -__git_ps1 ()
> +# Stores the text to be added to the bash prompt (branch name, status
> +# indicators, etc.) in the $__git_ps1_string variable.
> +__git_prompt_command ()
>  {
>  	local __git_dir=""
> +	__git_ps1_string=""
>  	__gitdir >/dev/null
>  	if [ -z "$__git_dir" ]; then
>  		return
> @@ -365,7 +371,18 @@ __git_ps1 ()
>  	fi
>  
>  	local f="$w$i$s$u"
> -	printf -- "${1:- (%s)}" "$c${b##refs/heads/}${f:+ $f}$r$p"
> +	__git_ps1_string="$c${b##refs/heads/}${f:+ $f}$r$p"
> +}
> +
> +# __git_ps1 accepts 0 or 1 arguments (i.e., format string)
> +# returns text to add to bash PS1 prompt (includes branch name)
> +__git_ps1 ()
> +{
> +	local __git_ps1_string
> +	__git_prompt_command
> +	if [ -n "$__git_ps1_string" ]; then
> +		printf -- "${1:- (%s)}" "$__git_ps1_string"
> +	fi

How hard/appropriate would it be to export individual parts of the prompt here? Something like:

__git_ps1_string_dirtystate="$i" __git_ps1_string_untrackedfiles="$u"

There have been requests in the past to let people individually colourise different bits of the prompt, which this would make practical.

>  }
>  
>  __gitcomp_1 ()
Previous: SZEDER GáborNext: SZEDER Gábor
Message 49 of 50 in “Bash prompt speedup”
  1. 00/19 Bash prompt speedupSZEDER Gábor, May 9, 2012
  2. 01/19 tests: move code to run tests under bash into a helper librarySZEDER Gábor, May 9, 2012
  3. 02/19 tests: add tests for the bash prompt functions in the completion scriptSZEDER Gábor, May 9, 2012
  4. Johannes SixtMay 9, 2012
  5. Junio C HamanoMay 9, 2012
  6. Johannes SixtMay 10, 2012
  7. Junio C HamanoMay 9, 2012
  8. SZEDER GáborMay 9, 2012
  9. 03/19 completion: use __gitdir() in _git_log()SZEDER Gábor, May 9, 2012
  10. Junio C HamanoMay 9, 2012
  11. SZEDER GáborMay 9, 2012
  12. 04/19 completion: respect $GIT_DIRSZEDER Gábor, May 9, 2012
  13. Johannes SixtMay 9, 2012
  14. Junio C HamanoMay 9, 2012
  15. 05/19 bash prompt: don't show the prompt when .git/HEAD is unreadableSZEDER Gábor, May 9, 2012
  16. Junio C HamanoMay 9, 2012
  17. SZEDER GáborMay 9, 2012
  18. 06/19 bash prompt: return early from __git_ps1() when not in a git repositorySZEDER Gábor, May 9, 2012
  19. 07/19 completion: make __gitdir() store repository path in $__git_dirSZEDER Gábor, May 9, 2012
  20. Junio C HamanoMay 9, 2012
  21. 08/19 completion: use $__git_dir instead of $(__gitdir)SZEDER Gábor, May 9, 2012
  22. Junio C HamanoMay 9, 2012
  23. SZEDER GáborMay 9, 2012
  24. Junio C HamanoMay 9, 2012
  25. SZEDER GáborMay 9, 2012
  26. 09/19 completion: platform-specific helper function to get physical pathSZEDER Gábor, May 9, 2012
  27. Johannes SixtMay 9, 2012
  28. 10/19 completion: use bash builtins to search for repositorySZEDER Gábor, May 9, 2012
  29. Junio C HamanoMay 9, 2012
  30. SZEDER GáborMay 9, 2012
  31. Junio C HamanoMay 9, 2012
  32. 11/19 bash prompt: use bash builtins to find out current branchSZEDER Gábor, May 9, 2012
  33. Junio C HamanoMay 9, 2012
  34. SZEDER GáborMay 9, 2012
  35. Junio C HamanoMay 9, 2012
  36. SZEDER GáborMay 9, 2012
  37. Junio C HamanoMay 9, 2012
  38. 12/19 bash prompt: use bash builtins to check whether inside git dirSZEDER Gábor, May 9, 2012
  39. Johannes SixtMay 9, 2012
  40. Junio C HamanoMay 9, 2012
  41. 13/19 bash prompt: check whether inside the worktree only when necessarySZEDER Gábor, May 9, 2012
  42. 14/19 bash prompt: use bash builtins to find out current branch during rebaseSZEDER Gábor, May 9, 2012
  43. 15/19 bash prompt: use bash builtins to get detached HEAD abbrev. object nameSZEDER Gábor, May 9, 2012
  44. 16/19 bash prompt: display stash and upstream state even inside the repositorySZEDER Gábor, May 9, 2012
  45. 17/19 bash prompt: use bash builtins to check stash stateSZEDER Gábor, May 9, 2012
  46. 18/19 bash prompt: avoid command substitution when checking for untracked filesSZEDER Gábor, May 9, 2012
  47. Junio C HamanoMay 9, 2012
  48. 19/19 bash prompt: alternative git prompt without command substitutionSZEDER Gábor, May 9, 2012
  49. Andrew SayersMay 9, 2012
  50. SZEDER GáborMay 9, 2012

Read the whole thread, see it on lore, or plain text.

$ cat FOOTERMessages come from the public archive at lore.kernel.org/git, fetched every hour. The front page is chosen and written each morning by an AI editor and can be wrong; the threads themselves are the record. About and API. For agents: an MCP server at https://gitlist.dev/mcp, and any thread, story or person page as Markdown by adding .md to its URL (or sending Accept: text/markdown). Details in /llms.txt.