run commands in default shell permalink

Runs the context value cmd in the default shell. On a sensible O/S, this is /bin/sh, or more recently zsh.

Do all the things you can’t do with cmd. cmd runs a program or executable, shell invokes the actual system shell. This means all your shell expressions are available, such as your favorite bashisms.

If you are just looking to run a command with arguments, you do not need to use shell, you can use cmd instead, which will incur less processing overhead.

set shell commands permalink

Input context can take one of two forms:

- name:
  description: passing cmd as a string doesn't save the output to context.
               prints stdout in real-time.
    cmd: 'echo ${PWD}'
- name:
  description: passing cmd as a dict allows you to specify if you want to
               save the output to context.
               prints command output only AFTER it has finished running.
      run: 'echo ${PWD}'
      save: True
      cwd: './set/current/working/dir/here'

All inputs support substitutions.

changing working directory permalink

If you specify cwd, it will change the current working directory to cwd to execute this command. The directory change is only for the duration of this step, not any subsequent steps.

When you do set cwd, the executable or program specified in run is relative to the cwd. cwd itself is relative to the over-all pypyr working directory.

If you do not specify cwd, it defaults to the current working directory, which is from wherever you are running pypyr.

capture shell output permalink

Be aware that if save is True, all of the command output ends up in memory. Don’t specify it unless your pipeline actually uses the stdout/stderr response in subsequent steps.

Keep in mind that if the invoked command has a non-zero return code pypyr will automatically raise a CalledProcessError and stop the pipeline - in other words, you do not have to set save to True to handle the output in case of error, the pipeline will stop and report the error automatically. If this is not the behavior you want, you can suppress errors with the swallow decorator and use the runErrors list on subsequent steps. Only use save: True when you actually need the stdout or stderr output.

If save is True, pypyr will save the output to context as follows:

    returncode: 0
    stdout: 'stdout str here. None if empty.'
    stderr: 'stderr str here. None if empty.'

cmdOut.returncode is the exit status of the called process. Typically 0 means OK. A negative value -N indicates that the child was terminated by signal N (POSIX only).

You can use cmdOut in subsequent steps like this:

- name: pypyr.steps.echo
  run: !py "cmdOut['returncode'] == 0"
    echoMe: "you'll only see me if cmd ran successfully with return code 0.
            the command output was: {cmdOut[stdout]}"

examples permalink

Example pipeline yaml using a pipe:

  - name:
    comment: if you have something pipey in working dir it should show up
      cmd: ls | grep pipe
  - name:
    comment: if you want to pass curlies to the shell, use sic strings
      cmd: !sic echo ${PWD};

See a worked example for shell pipeline power.

multiple inline shell statements permalink

Friendly reminder of the difference between separating your shell statements with ; or &&:

  • ; will continue to the next statement even if the previous command errored. It won’t exit with an error code if it wasn’t the last statement.
  • && stops and exits reporting error on first error.

You can change directory multiple times during this shell step using cd, but dir changes are only in scope for subsequent commands in this step, not for subsequent steps. Instead prefer using the cwd input as described above for an easy life, which sets the working directory for the entire step without you having to code it in with chained shell commands.

- name:
  comment: hop one up from current working dir.
           sic means won't attempt to 
           substitute {PWD} from context, so
           shell will interpret it as the $ENV.
    cmd: !sic echo ${PWD}; cd ../; echo ${PWD}
- name:
  comment: back to your current working dir
    cmd: !sic echo ${PWD}

see also

last updated on .