GitHub Actions shell: bash vs the default: -e and pipefail

On Linux and macOS runners a run: step without shell: is executed as bash -e {0}: the step stops at the first failing command, but not when the failure is inside a pipeline whose last command succeeds. Writing shell: bash changes the command to bash --noprofile --norc -eo pipefail {0}, so a failure anywhere in a pipeline fails the step.

The difference, reproduced

The same step script under both invocations ({0} is the script file the runner writes):

cat > step.sh <<'EOF'
grep error missing.log | sort
echo "still running after the failed grep"
EOF
echo "--- default:      bash -e {0}"
bash -e step.sh; echo "step exit status: $?"
echo "--- shell: bash:  bash --noprofile --norc -eo pipefail {0}"
bash --noprofile --norc -eo pipefail step.sh; echo "step exit status: $?"

--- default:      bash -e {0}
grep: missing.log: No such file or directory
still running after the failed grep
step exit status: 0
--- shell: bash:  bash --noprofile --norc -eo pipefail {0}
grep: missing.log: No such file or directory
step exit status: 2

With the default, grep fails but sort succeeds, the pipeline counts as successful, and the step goes on and passes. With shell: bash, the step fails right there.

Set it once for the whole workflow

defaults:
  run:
    shell: bash

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - run: curl -fsSL https://example.com/data.json | jq '.items | length'

Shells and their commands