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Storing build time in git notes with zsh

Playing around with git notes, having seen them on the github blog. I needed to update to git 1.7.2 (homebrew has it). The following shell command stores the run time of your specs inside a note on the latest commit:

{time rake spec} 2> >(tail -n 1 | cut -f 10 -d ' ' - |  git notes --ref=buildtime add -F - -f )

Breaking down the tricky bits:

{time rake spec} Honestly, I cargo culted the curly braces, and can’t find a good description of exactly what they do in this instance. It’s some sort of grouping thing: I found without them time didn’t apply properly.

2> time prints its output to STDERR, 2> redirects STDERR to the next argument. It is kind of like |, but for STDERR rather than STDOUT.

{time sleep 0.1} 2> /tmp/time.log

>( ... ) Rather than redirecting STDERR to a file, this allows us to pipe it in to more commands.

tail -n 1 rake spec also prints to STDERR, so pipe through tail to grab only the last line (which will be from time)

cut -f 10 -d ' ' - Split the line on a space character, choose the tenth column of the output from time, which is the total time taken. The trailing - says “read from STDIN”.

git notes --ref=buildtime add -F - -f Add a note to the latest commit (HEAD is default) in the buildtime namespace. -F - reads the note content from STDIN, which by now is only the final time taken for the spec run, and -f forces an update of the note if it already exists.

  • Posted on September 06, 2010
  • Tagged code, git, zsh
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