[PATCH v2 09/13] bash prompt: use bash builtins to get detached HEAD abbrev. object name

From: SZEDER Gábor <szeder@ira.uka.de>

When describing a detached HEAD according to the $GIT_PS1_DESCRIBE environment variable fails, __git_ps1() runs the '$(cut -c1-7 .git/HEAD)' command substitution to put the 7 hexdigits abbreviated commit object name in the prompt. This imposes the overhead of fork()ing a subshell and fork()+exec()ing 'cut'.

Thanks to the previous patch at this point the contents of HEAD has already been read into a variable, so we can get the 7 hexdigits using only parameter expansions, sparing the fork()+exec() overhead.

Since zsh doesn't implement substring expansion we can't just use ${head:0:7}, hence the "remove everything except the first 7 chars" parameter expansion combination.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
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 contrib/completion/git-prompt.sh | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)