Special Kwargs

These arguments alter a command’s behavior. They are not passed to the program. You can use them on any command that you run, but some may not be used together. sh will tell you if there are conflicts.

To set default special keyword arguments on every command run, you may use Default Arguments.

Controlling Output

_out

Default value: None

What to redirect STDOUT to. If this is a string, it will be treated as a file name. You may also pass a file object (or file-like object), an int (representing a file descriptor, like the result of os.pipe()), a io.StringIO object, or a callable.

import sh
sh.ls(_out="/tmp/output")

See also

Redirection

_err

Default value: None

What to redirect STDERR to. See _out.

_err_to_out

Default value: False

If True, duplicate the file descriptor bound to the process’s STDOUT also to STDERR, effectively causing STDERR and STDOUT to go to the same place.

_encoding

Default value: sh.DEFAULT_ENCODING

The character encoding of the process’s STDOUT. By default, this is the locale’s default encoding.

_decode_errors

New in version 1.07.0.

Default value: "strict"

This is how Python should handle decoding errors of the process’s output. By default, this is "strict", but you can use any value that’s valid to bytes.decode(), such as "ignore".

_tee

New in version 1.07.0.

Default value: None

As of 1.07.0, any time redirection is used, either for STDOUT or STDERR, the respective internal buffers are not filled. For example, if you’re downloading a file and using a callback on STDOUT, the internal STDOUT buffer, nor the pipe buffer be filled with data from STDOUT. This option forces one of stderr (_tee='err') or stdout (_tee='out' or _tee=True) to be filled anyways, in effect “tee-ing” the output into two places (the callback/redirect handler, and the internal buffers).

_truncate_exc

New in version 1.12.0.

Default value: True

Whether or not exception ouput should be truncated.

Execution

_fg

New in version 1.12.0.

Default value: False

Runs a command in the foreground, meaning it is spawned using os.spawnle(). The current process’s STDIN/OUT/ERR is os.dup2()’d to the new process and so the new process becomes the foreground of the shell executing the script. This is only really useful when you want to launch a lean, interactive process that sh is having trouble running, for example, ssh.

Warning

_fg=True side-steps a lot of sh’s functionality. You will not be returned a process object and most (likely all) other special kwargs will not work.

If you are looking for similar functionality, but still retaining sh’s features, use the following:

import sh
import sys
sh.your_command(_in=sys.stdin, _out=sys.stdout, _err=sys.stderr)

_bg

Default value: False

Runs a command in the background. The command will return immediately, and you will have to run RunningCommand.wait() on it to ensure it terminates.

See also

Background Processes.

_bg_exc

New in version 1.12.9.

Default value: True

Automatically report exceptions for the background command. If you set this to False you should make sure to call RunningCommand.wait() or you may swallow exceptions that happen in the background command.

_async

New in version 2.0.0.

Default value: False

Allows your command to become awaitable. Use in combination with _iter and async for to incrementally await output as it is produced.

_env

Default value: None

A dictionary defining the only environment variables that will be made accessible to the process. If not specified, the calling process’s environment variables are used.

Note

This dictionary is the authoritative environment for the process. If you wish to change a single variable in your current environement, you must pass a copy of your current environment with the overriden variable to sh.

See also

Environments

_timeout

Default value: None

How much time, in seconds, we should give the process to complete. If the process does not finish within the timeout, it will be sent the signal defined by _timeout_signal.

_timeout_signal

Default value: signal.SIGKILL

The signal to be sent to the process if _timeout is not None.

_cwd

Default value: None

A string that sets the current working directory of the process.

_ok_code

Default value: 0

Either an integer, a list, or a tuple containing the exit code(s) that are considered “ok”, or in other words: do not raise an exception. Some misbehaved programs use exit codes other than 0 to indicate success.

import sh
sh.weird_program(_ok_code=[0,3,5])

See also

Exit Codes & Exceptions

_new_session

Default value: False

Determines if our forked process will be executed in its own session via os.setsid().

Changed in version 2.0.0: The default value of _new_session was changed from True to False because it makes more sense for a launched process to default to being in the process group of python script, so that it receives SIGINTs correctly.

Note

If _new_session is False, the forked process will be put into its own group via os.setpgrp(). This way, the forked process, and all of it’s children, are always alone in their own group that may be signalled directly, regardless of the value of _new_session.

See also

Architecture Overview

_uid

New in version 1.12.0.

Default value: None

The user id to assume before the child process calls os.execv().

_preexec_fn

New in version 1.12.0.

Default value: None

A function to be run directly before the child process calls os.execv(). Typically not used by normal users.

_pass_fds

New in version 1.13.0.

Default value: {} (empty set)

A whitelist iterable of integer file descriptors to be inherited by the child. Passing anything in this argument causes _close_fds to be True.

_close_fds

New in version 1.13.0.

Default value: True

Causes all inherited file descriptors besides stdin, stdout, and stderr to be automatically closed. This option is automatically enabled when _pass_fds is given a value.

Communication

_in

Default value: None

Specifies an argument for the process to use as its standard input. This may be a string, a queue.Queue, a file-like object, or any iterable.

See also

Input via STDIN

_piped

Default value: None

May be True, "out", or "err". Signals a command that it is being used as the input to another command, so it should return its output incrementally as it receives it, instead of aggregating it all at once.

See also

Advanced Piping

_iter

Default value: None

May be True, "out", or "err". Puts a command in iterable mode. In this mode, you can use a for or while loop to iterate over a command’s output in real-time.

import sh
for line in sh.cat("/tmp/file", _iter=True):
    print(line)

See also

Incremental Iteration.

_iter_noblock

Default value: None

Same as _iter, except the loop will not block if there is no output to iterate over. Instead, the output from the command will be errno.EWOULDBLOCK.

import sh
import errno
import time

for line in sh.tail("-f", "stuff.log", _iter_noblock=True):
    if line == errno.EWOULDBLOCK:
        print("doing something else...")
        time.sleep(0.5)
    else:
        print("processing line!")

See also

Incremental Iteration.

_with

Default value: False

Explicitly tells us that we’re running a command in a with context. This is only necessary if you’re using a command in a with context and passing parameters to it.

import sh
with sh.contrib.sudo(password="abc123", _with=True):
    print(sh.ls("/root"))

See also

‘With’ Contexts

_done

New in version 1.11.0.

Default value: None

A callback that is always called when the command completes, even if it completes with an exit code that would raise an exception. After the callback is run, any exception that would be raised is raised.

The callback is passed the RunningCommand instance, a boolean indicating success, and the exit code.

Here’s an example of using _done to create a multiprocess pool, where sh.your_parallel_command is executed concurrently at no more than 10 at a time:

import sh
from threading import Semaphore

pool = Semaphore(10)

def done(cmd, success, exit_code):
    pool.release()

def do_thing(arg):
    pool.acquire()
    return sh.your_parallel_command(arg, _bg=True, _done=done)

procs = []
for arg in range(100):
    procs.append(do_thing(arg))

# essentially a join
[p.wait() for p in procs]

TTYs

_tty_in

Default value: False, meaning a os.pipe() will be used.

If True, sh creates a TTY for STDIN, essentially emulating a terminal, as if your command was entered from the commandline. This is necessary for commands that require STDIN to be a TTY.

_tty_out

Default value: True

If True, sh creates a TTY for STDOUT, otherwise use a os.pipe(). This is necessary for commands that require STDOUT to be a TTY.

See also

Why is _tty_out=True the default?

_unify_ttys

New in version 1.13.0.

Default value: False

If True, sh will combine the STDOUT and STDIN TTY into a single pseudo-terminal. This is sometimes required by picky programs which expect to be dealing with a single pseudo-terminal, like SSH.

See also

Entering an SSH password

_tty_size

Default value: (20, 80)

The (rows, columns) of stdout’s TTY. Changing this may affect how much your program prints per line, for example.

Performance & Optimization

_in_bufsize

Default value: 0

The STDIN buffer size. 0 for unbuffered, 1 for line buffered, anything else for a buffer of that amount.

_out_bufsize

Default value: 1

The STDOUT buffer size. 0 for unbuffered, 1 for line buffered, anything else for a buffer of that amount.

_err_bufsize

Default value: 1

Same as _out_bufsize, but with STDERR.

_internal_bufsize

Default value: 3 * 1024**2 chunks

How much of STDOUT/ERR your command will store internally. This value represents the number of bufsize chunks not the total number of bytes. For example, if this value is 100, and STDOUT is line buffered, you will be able to retrieve 100 lines from STDOUT. If STDOUT is unbuffered, you will be able to retrieve only 100 characters.

_no_out

New in version 1.07.0.

Default value: False

Disables STDOUT being internally stored. This is useful for commands that produce huge amounts of output that you don’t need, that would otherwise be hogging memory if stored internally by sh.

_no_err

New in version 1.07.0.

Default value: False

Disables STDERR being internally stored. This is useful for commands that produce huge amounts of output that you don’t need, that would otherwise be hogging memory if stored internally by sh.

_no_pipe

New in version 1.07.0.

Default value: False

Similar to _no_out, this explicitly tells the sh command that it will never be used for piping its output into another command, so it should not fill its internal pipe buffer with the process’s output. This is also useful for conserving memory.

Program Arguments

These are options that affect how command options are fed into the program.

_long_sep

New in version 1.12.0.

Default value: "="

This is the character(s) that separate a program’s long argument’s key from the value, when using kwargs to specify your program’s long arguments. For example, if your program expects a long argument in the form --name value, the way to achieve this would be to set _long_sep=" ".

import sh
sh.your_program(key=value, _long_sep=" ")

Would send the following list of arguments to your program:

["--key value"]

If your program expects the long argument name to be separate from its value, pass None into _long_sep instead:

import sh
sh.your_program(key=value, _long_sep=None)

Would send the following list of arguments to your program:

["--key", "value"]

_long_prefix

New in version 1.12.0.

Default value: "--"

This is the character(s) that prefix a long argument for the program being run. Some programs use single dashes, for example, and do not understand double dashes.

_arg_preprocess

New in version 1.12.0.

Default value: None

This is an advanced option that allows you to rewrite a command’s arguments on the fly, based on other command arguments, or some other variable. It is really only useful in conjunction with baking, and only currently used when constructing contrib wrappers.

Example:

import sh

def processor(args, kwargs):
    return args, kwargs

my_ls = sh.bake.ls(_arg_preprocess=processor)

Warning

The interface to the _arg_preprocess function may change without warning. It is generally only for internal sh use, so don’t use it unless you absolutely have to.

Misc

_log_msg

Default value: None

New in version 1.12.0.

This allows for a custom logging header for Command Class instances. For example, the default logging looks like this:

import logging
import sh

logging.basicConfig(level=logging.INFO)

sh.ls("-l")

INFO:sh.command:<Command '/bin/ls -l'>: starting process
INFO:sh.command:<Command '/bin/ls -l', pid 28952>: process started
INFO:sh.command:<Command '/bin/ls -l', pid 28952>: process completed

People can find this <Command .. section long and not relevant. _log_msg allows you to customize this:

import logging
import sh

logging.basicConfig(level=logging.INFO)

def custom_log(ran, call_args, pid=None):
    return ran

sh.ls("-l", _log_msg=custom_log)

INFO:sh.command:/bin/ls -l: starting process
INFO:sh.command:/bin/ls -l: process started
INFO:sh.command:/bin/ls -l: process completed

The first argument, ran, is the program’s execution string and arguments, as close as we can get it to be how you’d type in the shell. call_args is a dictionary of all of the special kwargs that were passed to the command. And pid is the process id of the forked process. It defaults to None because the _log_msg callback is actually called twice: first to construct the logger for the RunningCommand Class instance, before the process itself is spawned, then a second time after the process is spawned via OProc Class, when we have a pid.