spur 0.3.7

Run commands and manipulate files locally or over SSH using the same interface

To run echo locally:

import spur

shell = spur.LocalShell()
result = shell.run(["echo", "-n", "hello"])
print result.output # prints hello

Executing the same command over SSH uses the same interface – the only difference is how the shell is created:

import spur

shell = spur.SshShell(hostname="localhost", username="bob", password="password1")
with shell:
    result = shell.run(["echo", "-n", "hello"])
print result.output # prints hello

Installation

$ pip install spur

Shell constructors

LocalShell

Takes no arguments:

spur.LocalShell()

SshShell

Requires a hostname. Also requires some combination of a username, password and private key, as necessary to authenticate:

# Use a password
spur.SshShell(
    hostname="localhost",
    username="bob",
    password="password1"
)
# Use a private key
spur.SshShell(
    hostname="localhost",
    username="bob",
    private_key_file="path/to/private.key"
)
# Use a port other than 22
spur.SshShell(
    hostname="localhost",
    port=50022,
    username="bob",
    password="password1"
)

Optional arguments:

• connect_timeout – a timeout in seconds for establishing an SSH connection. Defaults to 60 (one minute).

• missing_host_key – by default, an error is raised when a host key is missing. One of the following values can be used to change the behaviour when a host key is missing:

• spur.ssh.MissingHostKey.raise_error – raise an error

• spur.ssh.MissingHostKey.warn – accept the host key and log a warning

• spur.ssh.MissingHostKey.accept – accept the host key

Shell interface

run(command, cwd, update_env, store_pid, allow_error, stdout, stderr)

Run a command and wait for it to complete. The command is expected to be a list of strings. Returns an instance of ExecutionResult.

result = shell.run(["echo", "-n", "hello"])
print result.output # prints hello

Note that arguments are passed without any shell expansion. For instance, shell.run(["echo", "$PATH"]) will print the literal string $PATH rather than the value of the environment variable $PATH.

Raises spur.NoSuchCommandError if trying to execute a non-existent command.

Optional arguments:

• cwd – change the current directory to this value before executing the command.

• update_env – a dict containing environment variables to be set before running the command. If there’s an existing environment variable with the same name, it will be overwritten. Otherwise, it is unchanged.

• store_pid – if set to True when calling spawn, store the process id of the spawned process as the attribute pid on the returned process object. Has no effect when calling run.

• allow_error – False by default. If False, an exception is raised if the return code of the command is anything but 0. If True, a result is returned irrespective of return code.

• stdout – if not None, anything the command prints to standard output during its execution will also be written to stdout using stdout.write.

• stderr – if not None, anything the command prints to standard error during its execution will also be written to stderr using stderr.write.

shell.run(*args, **kwargs) should behave similarly to shell.spawn(*args, **kwargs).wait_for_result()

spawn(command, cwd, update_env, store_pid, allow_error, stdout, stderr)

Behaves the same as run except that spawn immediately returns an object representing the running process.

Raises spur.NoSuchCommandError if trying to execute a non-existent command.

open(path, mode=”r”)

Open the file at path. Returns a file-like object.

Process interface

Returned by calls to shell.spawn. Has the following attributes:

• pid – the process ID of the process. Only available if store_pid was set to True when calling spawn.

Has the following methods:

• is_running() – return True if the process is still running, False otherwise.

• stdin_write(value) – write value to the standard input of the process.

• wait_for_result() – wait for the process to exit, and then return an instance of ExecutionResult. Will raise RunProcessError if the return code is not zero and shell.spawn was not called with allow_error=True.

• send_signal(signal) – sends the process the signal signal. Only available if store_pid was set to True when calling spawn.

Classes

ExecutionResult

ExecutionResult has the following properties:

• return_code – the return code of the command

• output – a string containing the result of capturing stdout

• stderr_output – a string containing the result of capturing stdout

It also has the following methods:

• to_error() – return the corresponding RunProcessError. This is useful if you want to conditionally raise RunProcessError, for instance:

result = shell.run(["some-command"], allow_error=True)
if result.return_code > 4:
    raise result.to_error()

RunProcessError

A subclass of RuntimeError with the same properties as ExecutionResult:

• return_code – the return code of the command

• output – a string containing the result of capturing stdout

• stderr_output – a string containing the result of capturing stdout

NoSuchCommandError

NoSuchCommandError has the following properties:

• command – the command that could not be found

API stability

Using the the terminology from Semantic Versioning, if the version of spur is X.Y.Z, then X is the major version, Y is the minor version, and Z is the patch version.

While the major version is 0, incrementing the patch version indicates a backwards compatible change. For instance, if you’re using 0.3.1, then it should be safe to upgrade to 0.3.2.

Incrementing the minor version indicates a change in the API. This means that any code using previous minor versions of spur may need updating before it can use the current minor version.

Undocumented features

Some features are undocumented, and should be considered experimental. Use them at your own risk. They may not behave correctly, and their behaviour and interface may change at any time.

Troubleshooting

I get the error “Connection refused” when trying to connect to a virtual machine using a forwarded port on localhost

Try using "127.0.0.1" instead of "localhost" as the hostname.

I get the error “Connection refused” when trying to execute commands over SSH

Try connecting to the machine using SSH on the command line with the same settings. For instance, if you’re using the code:

shell = spur.SshShell(
        hostname="remote",
        port=2222,
        username="bob",
        private_key_file="/home/bob/.ssh/id_rsa"
    )
with shell:
    result = shell.run(["echo", "hello"])

Try running:

ssh bob@remote -p 2222 -i /home/bob/.ssh/id_rsa

If the ssh command succeeds, make sure that the arguments to ssh.SshShell and the ssh command are the same. If any of the arguments to ssh.SshShell are dynamically generated, try hard-coding them to make sure they’re set to the values you expect.