Generic scripts for linting and testing

[pboothe]

Test hooks for json, yml, travis.yml, python, go

The yml and json are both raw hooks, but the others are even fleshed out

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This change is 

[stephen-soltesz]

It looks like there is a similar pattern in the two files:

• check for file type, take type-specific action.

pre-commit may fail, pre-commit-msg just outputs txt.

To prevent duplication or divergence between the files, I'm imagining a common file that manages each type-specific action called in a separate script (e.g. .git/hooks/cmd-lint-travis). The difference at call time would be "capture exit code" (for pre-commit) or "capture output" (for pre-commit-msg).

-- since having this now is better and we can work towards a solution with more share logic.

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Reviewed 2 of 4 files at r1.
Review status: 2 of 4 files reviewed at latest revision, 4 unresolved discussions.

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prepare-commit-msg, line 51 at r1 (raw file):

  if git ls-files | grep -q '\.py$'; then
    if [[ -x ./python-prepare-commit-msg ]]; then
      ./python-prepare-commit-msg

What is the PWD at this point? Above the PWD appears to be implicitly the root of the current repo. Here it looks like the .git/hooks/ dir? Or, it's a special case to handle running from the git-hooks repo itself? Please add a comment to clarify.

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prepare-commit-msg, line 56 at r1 (raw file):

    else
      echo "No python-prepare-commit-msg found, but one should exist." 1>&2
      false

What does false do in this context?

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prepare-commit-msg, line 64 at r1 (raw file):

  if git ls-files | grep -q '\.go$'; then
    if [[ -x ./go-prepare-commit-msg ]]; then
      ./go-prepare-commit-msg

Yeah, I'm still confused about PWD here.

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README.md, line 8 at r1 (raw file):

to test.  The following commands will get that done:
```bash
  ln -s ../../git-hooks/pre-commit .git/hooks/pre-commit

Can I run these commands multiple times safely? Will it replace existing hooks?

Please prefer long form option names when available, i.e. --symbolic --force

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