Commit a file if it changed#

This recipe runs a Python script to update a README, then commits it back to the parent repo but only if it has changed:

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on:
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  push:
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    branches:
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    - master
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# ...
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    - name: Update README
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      run: python update_readme.py --rewrite
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    - name: Commit README back to the repo
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      run: |-
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        git config --global user.email "readme-bot@example.com"
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        git config --global user.name "README-bot"
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        git diff --quiet || (git add README.md && git commit -m "Updated README")
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        git push

My first attempt threw an error if I tried o run git commit -m ... and the README had not changed.

It turns out git diff --quiet exits with a 1 exit code if anything has changed, so this recipe adds the file and commits it only if something differs:

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git diff --quiet || (git add README.md && git commit -m "Updated README")

Mikeal Rogers has a publish-to-github-action which uses a slightly different pattern:

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# publish any new files
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git checkout master
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git add -A
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timestamp=$(date -u)
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git commit -m "Automated publish: ${timestamp} ${GITHUB_SHA}" || exit 0
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git pull --rebase publisher master
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git push publisher master

Cleanest example yet: https://github.com/simonw/coronavirus-data-gov-archive/blob/master/.github/workflows/scheduled.yml

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name: Fetch latest data
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on:
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  push:
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  repository_dispatch:
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  schedule:
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    - cron:  '25 * * * *'
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jobs:
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  scheduled:
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    runs-on: ubuntu-latest
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    steps:
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    - name: Check out this repo
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      uses: actions/checkout@v2
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    - name: Fetch latest data
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      run: |-
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        curl https://c19downloads.azureedge.net/downloads/data/data_latest.json | jq . > data_latest.json
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        curl https://c19pub.azureedge.net/utlas.geojson | gunzip | jq . > utlas.geojson
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        curl https://c19pub.azureedge.net/countries.geojson | gunzip | jq . > countries.geojson
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        curl https://c19pub.azureedge.net/regions.geojson | gunzip | jq . > regions.geojson
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    - name: Commit and push if it changed
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      run: |-
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        git config user.name "Automated"
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        git config user.email "actions@users.noreply.github.com"
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        git add -A
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        timestamp=$(date -u)
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        git commit -m "Latest data: ${timestamp}" || exit 0
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        git push