# 2.5.13.49. SetPropertyFromCommand

class buildbot.steps.shell.SetPropertyFromCommand

This buildstep is similar to `ShellCommand`, except that it captures the output of the command into a property. It is usually used like this:

    from buildbot.plugins import steps

    f.addStep(steps.SetPropertyFromCommand(command="uname -a", property="uname"))

This runs `uname -a` and captures its stdout, stripped of leading and trailing whitespace, in the property `uname`. To avoid stripping, add `strip=False`.

The `property` argument can be specified as an Interpolate object, allowing the property name to be built from other property values.

Passing `includeStdout=False` (defaults to `True`) stops capture from stdout.

Passing `includeStderr=True` (defaults to `False`) allows capture from stderr.

The more advanced usage allows you to specify a function to extract properties from the command output. Here you can use regular expressions, string interpolation, or whatever you would like. In this form, `extract_fn` should be passed, and not `Property`. The `extract_fn` function is called with three arguments: the exit status of the command, its standard output as a string, and its standard error as a string. It should return a dictionary containing all new properties.

Note that passing in `extract_fn` will set `includeStderr` to `True`.

    def glob2list(rc, stdout, stderr):
        jpgs = [l.strip() for l in stdout.split('\n')]
        return {'jpgs': jpgs}

    f.addStep(SetPropertyFromCommand(command="ls -1 *.jpg", extract_fn=glob2list))

Note that any ordering relationship of the contents of stdout and stderr is lost. For example, given:

    f.addStep(SetPropertyFromCommand(
        command="echo output1; echo error >&2; echo output2",
        extract_fn=my_extract))

Then `my_extract` will see `stdout="output1\noutput2\n"` and `stderr="error\n"`.

Avoid using the `extract_fn` form of this step with commands that produce a great deal of output, as the output is buffered in memory until complete.