Tutorial

xonsh is a shell language and command prompt. Unlike other shells, xonsh is based on Python, with additional syntax added that makes calling subprocess commands, manipulating the environment, and dealing with the file system easy. The xonsh command prompt gives users interactive access to the xonsh language.

While all Python code is also xonsh, not all POSIX shell code can be used in xonsh. That would defeat the purpose, and Python is better anyway! Still, xonsh is compatible with shell commands in the ways that matter, such as for running commands, reading the environment, and utilizing tab completion.

The purpose of this tutorial is to teach you xonsh. There are many excellent guides out there for learning Python, and this will not join their ranks. Similarly, you’d probably get the most out of this tutorial if you have already used a command prompt or interactive interpreter.

Let’s dive in!

Starting xonsh

Assuming you have successfully installed xonsh, you can start up the xonsh interpreter via the xonsh command. Suppose you are in a lesser terminal:

$ xonsh
snail@home ~ @ █

Now we are in a xonsh shell. Our username happens to be snail, our hostname happens to be home, and we are in our home directory (~). Alternatively, you can setup your terminal emulator (xterm, gnome-terminal, etc) to run xonsh automatically when it starts up. This is recommended.

Basics

The xonsh language is based on Python, and the xonsh shell uses Python to interpret any input it receives. This makes simple things simple and we are able to install and import modules, operate with values and objects, and use other built-in Python functionality:

@ 1 + 1

@ xpip install requests
@ import requests
@ requests.get("https://xon.sh").status_code

@ print(1 if True else 2)

@ for i, x in enumerate('xonsh'):
      # For easier indentation, Shift+Tab will enter 4 spaces.
      print(i, x)

@ def f():
      return "xonsh"
  f()

On the other hand, you can execute commands:

@ echo hello
@ cd $HOME
@ id $(whoami) > ~/id.txt
@ cat /etc/passwd | grep root

Finally, you can use everything together:

@ name = 'snail'
  echo @(name) > /tmp/@(name)

@ $PATH.append('/tmp')

@ @.imp.json.loads($(echo '{"a":1}'))

But let’s go through everything step by step.

Xonsh Session Interface

Each session has a special global object @ that provides instant functionality. It gives you access to different parts of the current session. For example, you can use @.env to change environment variables, or @.imp to import libraries. You will learn more about this in the following sections.

@ help(@)
Help on XonshSessionInterface in module xonsh.built_ins object: ...
@ @.imp.json.loads('{"conch":"snail"}')
{"conch":"snail"}
@ @.env.get('HOME')
'/home/snail'

Environment Variables

Environment variables are written as $ followed by a name. For example, $HOME, $PWD, and $PATH.

@ $HOME
'/home/snail'

You can set (and export) environment variables like you would set any other variable in Python. The same is true for deleting them too.

@ $GOAL = 'Master the shell'
@ print($GOAL)
Master the shell
@ del $GOAL

@ $NUM = "123"
@ $EXT = $NUM + "456"
@ $EXT
'123456'
@ $FNUM = f"{$NUM}456" # Not working with Python 3.12+ (https://github.com/xonsh/xonsh/issues/5166).
@ $FNUM = "{FILLME}456".format(FILLME=$NUM)
@ $FNUM
'123456'
@ "%s456" % $NUM
'123456'

Very nice.

Note

To update os.environ when the xonsh environment changes set $UPDATE_OS_ENVIRON to True.

The Environment Itself @.env

All environment variables live in the built-in @.env mapping. You can access this mapping directly, but in most situations, you shouldn’t need to.

If you want for example to check if an environment variable is present in your current session (say, in your awesome new xonsh script) you can use the membership operator:

@ 'HOME' in @.env
# True

To get information about a specific environment variable you can use the help() method.

@ @.env.help('XONSH_DEBUG')

One helpful method is swap(). It can be used to temporarily set an environment variable:

@ with @.env.swap(SOMEVAR='foo'):
      echo $SOMEVAR

foo
@ echo $SOMEVAR
$SOMEVAR
@

You can also change the value using preset on the command line:

@ $HELLO='snail' xonsh -c 'echo Hello $HELLO'
Hello snail

Environment Lookup with ${<expr>}

The $NAME is great as long as you know the name of the environment variable you want to look up. But what if you want to construct the name programmatically, or read it from another variable? Enter the ${} operator.

We can place any valid Python expression inside of the curly braces in ${<expr>}. This result of this expression will then be used to look up a value in the environment. Here are a couple of examples in action:

@ x = 'USER'
@ ${x}
'snail'
@ ${'HO' + 'ME'}
'/home/snail'

Not bad, xonsh, not bad.

Environment Types

Environment variables in xonsh are not limited to strings – they can hold any Python type: strings, numbers, lists, and arbitrary objects. When a variable is used as a subprocess argument, xonsh converts it to a string automatically:

@ $MY_STR = 'hello'
@ $MY_NUM = 42
@ $MY_LIST = [1, 2, 3]
@ showcmd echo $MY_STR $MY_NUM $MY_LIST
['echo', 'hello', '42', '[1, 2, 3]']

$PATH is an EnvPath object – a special list that makes it easy to add and remove directories:

@ $PATH
['/usr/local/bin', '/usr/bin', '/bin']
@ $PATH.append('/opt/mytools/bin')
@ $PATH.insert(0, '$HOME/.local/bin')
@ $PATH
['/home/snail/.local/bin', '/usr/local/bin', '/usr/bin', '/bin',
'/opt/mytools/bin']

Any variable whose name ends in PATH or DIRS is automatically treated as an EnvPath.

Note

In subprocess mode, referencing an undefined environment variable will produce an empty string. In Python mode, however, a KeyError will be raised if the variable does not exist in the environment.

You can also register custom variables with types and documentation, create callable variables with dynamic values, and more – see Environment for the full details.

Python-mode vs Subprocess-mode

It is sometimes helpful to make the distinction between lines that operate in pure Python mode and lines that use shell-specific syntax, edit the execution environment, and run commands. Unfortunately, it is not always clear from the syntax alone what mode is desired. This ambiguity stems from most command line utilities looking a lot like Python operators.

Take the case of ls -l. This is valid Python code, though it could have also been written as ls - l or ls-l. So how does xonsh know that ls -l is meant to be run in subprocess-mode?

For any given line that only contains an expression statement (expr-stmt, see the Python AST docs for more information), if all the names cannot be found as current variables xonsh will try to parse the line as a subprocess command instead. In the above, if ls and l are not variables, then subprocess mode will be attempted. If parsing in subprocess mode fails, then the line is left in Python-mode.

In the following example, we will list the contents of the directory with ls -l. Then we’ll make new variable names ls and l and then subtract them. Finally, we will delete ls and l and be able to list the directories again.

@ # this will be in subproc-mode, because ls doesn't exist
@ ls -l
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh
@ # set ls and l variables to force python-mode
@ ls = 44
@ l = 2
@ ls -l
42
@ # deleting ls will return us to subproc-mode
@ del ls
@ ls -l
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh

The determination between Python- and subprocess-modes is always done in the safest possible way. If anything goes wrong, it will favor Python-mode. The determination between the two modes is done well ahead of any execution. You do not need to worry about partially executed commands - that is impossible.

Note

If you would like to explicitly run a subprocess command, you can always use the formal xonsh subprocess syntax that we will see in the following sections. For example: ![ls -l].

Subprocess

Running Commands

As a shell, xonsh is meant to make running commands easy and fun. Running subprocess commands should work like in any other shell.

@ echo "Yoo hoo"
Yoo hoo
@ cd xonsh
@ ls
build  docs     README.rst  setup.py  xonsh           __pycache__
dist   LICENSE  scripts     tests     xonsh.egg-info
@ dir scripts
xonsh  xonsh.bat
@ git status
On branch main
@ exit

This should feel very natural.

Note

Access the last run subprocess command using @.lastcmd; e.g. to get the return code, run @.lastcmd.rtn.

Strings and Quoting in Subprocess Mode

Single or double quotes can be used to remove the special meaning of certain characters or words to xonsh. If a subprocess command contains characters that collide with xonsh syntax then quotes must be used to force xonsh to not interpret them.

@ echo ${
SyntaxError
@ echo '${'
${

The contents of the string are passed directly to the subprocess command as a single argument. So whenever you are in doubt, or if there is a xonsh syntax error because of a filename, just wrap the offending portion in a string.

A common use case for this is files with spaces in their names:

@ touch "sp ace"
@ ls -l
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 17:50 sp ace
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh

By default, the name of an environment variable inside a string will be replaced by the contents of that variable (in subprocess mode only). For example:

@ print("my home is $HOME")
my home is $HOME
@ echo "my home is $HOME"
my home is /home/snail

You can avoid this expansion within a particular command by forcing the strings to be evaluated in Python mode using the @() syntax:

@ echo "my home is $HOME"
my home is /home/snail
@ echo @("my home is $HOME")
my home is $HOME

Note

You can also disable environment variable expansion completely by setting $EXPAND_ENV_VARS to False.

Xonsh supports Python string prefixes in subprocess arguments:

  • r"" — raw, no escapes (r'\n' stays as \n)

  • f"" — formatted, with {expr} substitution

  • p"" — path, returns pathlib.Path with $ENV expansion

These can be combined (fr"", pf"", pr""). For example:

@ echo r'no\escape'
no\escape
@ echo f"{'hello':>10}"
     hello
@ p"/tmp" / "file.txt"
PosixPath('/tmp/file.txt')
@ name = "docs"
@ pf"$HOME/{name}"
PosixPath('/Users/snail/docs')

See Subprocess Strings for the full reference table of how each prefix affects environment variable substitution, brace formatting, and escapes.

Captured Subprocess with $() and !()

The $(<expr>) operator in xonsh executes a subprocess command and captures some information about that command.

The $() syntax captures and returns the standard output stream of the command as a Python string. For example,

@ $(ls -l)
'total 0\n-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh\n'

Note

By default the output is represented as one single block of output with new line characters. You can set $XONSH_SUBPROC_OUTPUT_FORMAT to list_lines to have a list of distinct lines in the commands like du -h $(ls).

The !() syntax captured more information about the command, as an instance of a class called CommandPipeline. This object contains more information about the result of the given command, including the return code, the process id, the standard output and standard error streams, and information about how input and output were redirected. For example:

@ !(ls nonexistent_directory)
CommandPipeline(
   pid=26968,
   returncode=2,
   args=['ls', 'nonexistent_directory'],
   alias=['ls', '--color=auto', '-v'],
   timestamps=[1485235484.5016758, None],
   executed_cmd=['ls', '--color=auto', '-v', 'nonexistent_directory'],
   input=None,
   output=,
   errors=None
)

The captured object !() operator allows for non-blocking execution. You can call a long-running command, intersperse other commands and read the captured output later:

@ p = !(echo snail)
@ p.output
''
@ p.end()
@ p.output
'snail'

You can force xonsh to block and wait for the command to complete by asking for the return code, printing the object or reading the out attribute:

@ p = !(echo snail)
@ p.out
'snail'
@ p = !(echo party)
@ p.rtn
0
@ p.output
'party'

This object will be “truthy” if its return code was 0, and it is equal (via ==) to its return code. It also hashes to its return code. Converting the object to the string will return the output. This allows for some interesting new kinds of interactions with subprocess commands, for example:

def check_file(file):
    if !(test -e @(file)):
        if !(test -f @(file)) or !(test -d @(file)):
            print("File is a regular file or directory")
        else:
            print("File is not a regular file or directory")
    else:
        print("File does not exist")

def wait_until_google_responds():
    while not !(ping -c 1 google.com):
        sleep 1

If you iterate over the CommandPipeline object, it will yield lines of its output. Using this, you can quickly and cleanly process output from commands. Additionally, these objects expose a method itercheck, which behaves the same as the built-in iterator but raises XonshCalledProcessError if the process had a nonzero return code.

def get_wireless_interface():
    """Returns devicename of first connected wifi, None otherwise"""
    for line in !(nmcli device):
        dev, typ, state, conn_name = line.split(None, 3)
        if typ == 'wifi' and state == 'connected':
            return dev

def grep_path(path, regexp):
    """Recursively greps `path` for perl `regexp`

    Returns a dict of 'matches' and 'failures'.
    Matches are files that contain the given regexp.
    Failures are files that couldn't be scanned.
    """
    matches = []
    failures = []

    try:
        for match in !(grep -RPl @(regexp) @(str(path))).itercheck():
            matches.append(match)
    except XonshCalledProcessError as error:
        for line in error.stderr.split('\n'):
            if not line.strip():
                continue
            filename = line.split('grep: ', 1)[1].rsplit(':', 1)[0]
            failures.append(filename)
    return {'matches': matches, 'failures': failures}

The $() and !() operators are expressions themselves. This means that we can assign the results to a variable or perform any other manipulations we want.

@ x = $(ls -l)
@ print(x.upper())
TOTAL 0
-RW-RW-R-- 1 SNAIL SNAIL 0 MAR  8 15:46 XONSH
@ y = !(ls -l)
@ print(y.returncode)
0
@ print(y.rtn)  # alias to returncode
0

Warning

Job control is not implemented for captured subprocesses.

While in subprocess-mode or inside of a captured subprocess, we can always still query the environment with $NAME variables or the ${} syntax, or inject Python values with the @() operator:

@ $(echo $HOME)
'/home/snail'

Threading

If you want to work more closely with captured commands, you need to know about threading. Xonsh has a threading prediction mechanism that allows it to understand which commands can capture everything. For example, the echo command has no interaction with the user and is capturable. However, some tools have mixed behavior and can be run for either interactive or non-interactive tasks. The best example of this is ssh, which allows for remote terminal sessions and executing commands.

To handle different types of tasks, xonsh has the @thread and @unthread built-in decorator aliases. If you need to capture the output from an interactive tool that has a capturable mode use @thread to run:

@ !(@thread ssh host -T 'echo remote')
CommandPipeline(output="remote")

Uncaptured Subprocess with $[] and ![]

Uncaptured subprocesses are denoted with the $[] and ![] operators. They are the same as $() captured subprocesses in almost every way. The only difference is that the subprocess’s stdout passes directly through xonsh and to the screen. The return value of $[] is always None.

In the following, we can see that the results of $[] are automatically printed, and that the return value is not a string.

@ x = $[ls -l]
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh
@ x is None
True

The ![] operator is similar to the !() in that it returns an object containing information about the result of executing the given command. However, its standard output and standard error streams are directed to the terminal, and the resulting object is not displayed. For example

@ x = ![ls -l] and ![echo "hi"]
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh
hi

Python Evaluation with @()

The @(<expr>) operator form works in subprocess mode, and will evaluate arbitrary Python code. The result is appended to the subprocess command list. If the result is a string or bytes, it is appended to the argument list. If the result is a list or other non-string sequence, the contents are converted to strings and appended to the argument list in order. If the result in the first position is a function, it is treated as an alias (see the section on Aliases below), even if it was not explicitly added to the aliases mapping. Otherwise, the result is automatically converted to a string. For example,

@ x = 'xonsh'
@ y = 'party'
@ echo @(x + ' ' + y)
xonsh party
@ echo @(2+2)
4
@ echo @([42, 'yo'])
42 yo
echo "hello" | @(lambda args, stdin=None: stdin.read().strip() + " world\n")
hello world
@ @(['echo', 'hello', 'world'])
hello world
@ @('echo hello world')  # note that strings are not split automatically
xonsh: subprocess mode: command not found: echo hello world

This syntax can be used inside of a captured or uncaptured subprocess, and can be used to generate any of the tokens in the subprocess command list.

@ out = $(echo @(x + ' ' + y))
@ out
'xonsh party'
@ @("ech" + "o") "hey"
hey

Thus, @() allows us to create complex commands in Python-mode and then feed them to a subprocess as needed. For example:

for i in range(20):
    $[touch @('file%02d' % i)]

The @() syntax may also be used inside of subprocess arguments, not just as a stand-alone argument. For example:

@ x = 'hello'
@ echo /path/to/@(x)
/path/to/hello

When used inside of a subprocess argument and <expr> evaluates to a non-string iterable, @() will expand to the outer product of all given values:

@ echo /path/to/@(['hello', 'world'])
/path/to/hello /path/to/world

@ echo @(['a', 'b']):@('x', 'y')
a:x a:y b:x b:y

Command Substitution with @$()

A common use of the @() and $() operators is allowing the output of a command to replace the command itself (command substitution): @([i.strip() for i in $(cmd).split()]). Xonsh offers a short-hand syntax for this operation: @$(cmd).

Consider the following example:

@ # this returns a string representing stdout
@ $(which ls)
'ls --color=auto'

@ # this attempts to run the command, but as one argument
@ # (looks for 'ls --color=auto' with spaces)
@ @($(which ls))
xonsh: subprocess mode: command not found: ls --color=auto

@ # this actually executes the intended command
@ @([i.strip() for i in $(which ls).split()])
some_file  some_other_file

@ # this does the same thing, but is much more concise
@ @$(which ls)
some_file  some_other_file

Nesting Subprocesses

Though I am begging you not to abuse this, it is possible to nest the subprocess operators that we have seen so far ($(), $[], ${}, @(), @$()). An instance of ls -l that is on the wrong side of the border of the absurd is shown below:

@ $[@$(which @($(echo ls).strip())) @('-' + $(printf 'l'))]
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh

With great power, and so forth…

Note

Nesting these subprocess operators inside of $() and/or $[] works because the contents of those operators are executed in subprocess mode. Since @() and ${} run their contents in Python mode, it is not possible to nest other subprocess operators inside of them.

To understand how xonsh executes the subprocess commands try to set $XONSH_SUBPROC_TRACE to True:

@ $XONSH_SUBPROC_TRACE = True
@ $[@$(which @($(echo ls).strip())) @('-' + $(printf 'l'))]
TRACE SUBPROC: (['echo', 'ls'],)
TRACE SUBPROC: (['which', 'ls'],)
TRACE SUBPROC: (['printf', 'l'],)
TRACE SUBPROC: (['ls', '--color=auto', '-v', '-l'],)
total 0
-rw-rw-r-- 1 snail snail 0 Mar  8 15:46 xonsh

Pipes

In subprocess-mode, xonsh allows you to use the | character to pipe together commands as you would in other shells.

@ env | uniq | sort | grep PATH
DATAPATH=/usr/share/MCNPX/v260/Data/
DEFAULTS_PATH=/usr/share/gconf/awesome-gnome.default.path
LD_LIBRARY_PATH=/home/snail/.local/lib:
MANDATORY_PATH=/usr/share/gconf/awesome-gnome.mandatory.path
PATH=/home/snail/.local/bin:/home/snail/sandbox/bin:/usr/local/bin
XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0
XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0

This is only available in subprocess-mode because | is otherwise a Python operator. If you are unsure of what pipes are, there are many great references out there. You should be able to find information on StackOverflow or Google.

Logical Subprocess And/Or

Subprocess-mode also allows you to use the and operator to chain together subprocess commands. The truth value of a command is evaluated as whether its return code is zero (i.e. proc.returncode == 0). Like in Python, if the command evaluates to False, subsequent commands will not be executed. For example, suppose we want to lists files that may or may not exist:

@ touch exists
@ ls exists and ls doesnt
exists
/bin/ls: cannot access doesnt: No such file or directory

However, if you list the file that doesn’t exist first, you would have only seen the error:

@ ls doesnt and ls exists
/bin/ls: cannot access doesnt: No such file or directory

Also, don’t worry. Xonsh directly translates the && operator into and for you. It is less Pythonic, of course, but it is your shell!

Much like with and, you can use the or operator to chain together subprocess commands. The difference, to be certain, is that subsequent commands will be executed only if the if the return code is non-zero (i.e. a failure). Using the file example from above:

@ ls exists or ls doesnt
exists

This doesn’t even try to list a non-existent file! However, if you list the file that doesn’t exist first, you will see the error and then the file that does exist:

@ ls doesnt or ls exists
#/bin/ls: cannot access doesnt: No such file or directory
exists

Xonsh also directly translates the || operator into or, too.

Input/Output Redirection

xonsh also allows you to redirect stdin, stdout, and/or stderr. This allows you to control where the output of a command is sent, and where it receives its input from. xonsh has its own syntax for these operations, but, for compatibility purposes, xonsh also support POSIX-like syntax.

The basic operations are “write to” (>), “append to” (>>), and “read from” (<). The details of these are perhaps best explained through examples.

Note

The target of the redirection should be separated by a space, otherwise xonsh will raise a SyntaxError.

Redirecting stdout. The operators >, out>, o>, and 1> (POSIX) all execute cmd and write its regular output (stdout) to a file, creating it if it does not exist:

@ cmd > output.txt

These can be made to append to output.txt instead of overwriting its contents by replacing > with >> (note that >> will still create the file if it does not exist).

Redirecting stderr. The operators err>, e>, and 2> (POSIX) all execute cmd and write its error output (stderr) to a file, creating it if it does not exist:

@ cmd err> errors.txt

As above, replacing > with >> will cause the error output to be appended to errors.txt, rather than replacing its contents.

Combining streams. The operators all>, a>, and &> (POSIX) all send both regular output and error output to the same location:

@ cmd all> combined.txt

Merging stderr into stdout. The operators err>out, err>o, e>out, e>o, and 2>&1 (POSIX) all explicitly merge stderr into stdout so that error messages are reported to the same location as regular output:

@ cmd err>out
@ cmd err>out | cmd2

Merging stdout into stderr. Similarly, the operators out>err, out>e, o>err, o>e, and 1>&2 (POSIX) all send stdout to stderr:

@ cmd out>err

Routing streams into a pipe. The operators a>p (all>p) and e>p (err>p) add stderr to the following | pipe. The pipe still carries stdout as usual, unless an explicit o> file diverts stdout elsewhere — which makes e>p useful for the pattern of sending stdout to a file while stderr flows into the pipe. These operators require a following pipe.

@ cmd a>p | cmd2                     # stdout + stderr into the pipe
@ cmd e>p | grep warning             # same — pipe carries both streams
@ cmd o> out.txt e>p | grep warning  # stdout to file, stderr into the pipe

Redirecting stdin is also possible to have a command read its input from a file, rather than from stdin. The following examples demonstrate two ways to accomplish this:

@ cmd < input.txt
@ < input.txt cmd

Combining I/O redirects is also possible. Below is one example of a complicated redirect.

@ cmd1 e>o < input.txt | cmd2 > output.txt e>> errors.txt

This line will run cmd1 with the contents of input.txt fed in on stdin, and will pipe all output (stdout and stderr) to cmd2; the regular output of this command will be redirected to output.txt, and the error output will be appended to errors.txt.

Job Control

You can get a listing of all currently running jobs with the jobs command.

Each job has a unique identifier (starting with 1 and counting upward). By default, the fg and bg commands operate on the job that was started most recently. You can bring older jobs to the foreground or background by specifying the appropriate ID; for example, fg 1 brings the job with ID 1 to the foreground. Additionally, specify “+” for the most recent job and “-” for the second most recent job.

Background Jobs

Typically, when you start a program running in xonsh, xonsh itself will pause and wait for that program to terminate. Sometimes, though, you may want to continue giving commands to xonsh while that program is running. In subprocess mode, you can start a process “in the background” (i.e., in a way that allows continued use of the shell) by adding an ampersand (&) to the end of your command. Background jobs are very useful when running programs with graphical user interfaces.

The following shows an example with emacs.

@ emacs &
@

Note that the prompt is returned to you after emacs is started.

Normally background commands end upon the shell closing. To allow a background command to continue running after the shell has exited, use the disown command which accepts either no arguments (to disown the most recent job) or an arbitrary number of job identifiers.

Foreground Jobs

If you start a program in the foreground (with no ampersand), you can suspend that program’s execution and return to the xonsh prompt by pressing Control-Z. This will give control of the terminal back to xonsh, and will keep the program paused in the background.

Note

Suspending processes via Control-Z is not yet supported when running on Windows.

To unpause the program and bring it back to the foreground, you can use the fg command. To unpause the program have it continue in the background (giving you continued access to the xonsh prompt), you can use the bg command.

Filename Globbing

Normal Globbing

Filename globbing with the * character is also allowed in subprocess-mode. This simply uses Python’s glob module under-the-covers. See there for more details. As an example, start with a lovely bunch of xonshs:

@ touch xonsh conch konk quanxh
@ ls
conch  konk  quanxh  xonsh
@ ls *h
conch  quanxh  xonsh
@ ls *o*
conch  konk  xonsh

In subprocess mode, normal globbing happens without any special syntax. However, there is backtick syntax that is available inside Python mode as well as subprocess mode. This can be done using g``:

@ touch a aa aaa aba abba aab aabb abcba
@ ls a*b*
aab  aabb  aba  abba  abcba
@ ls g`a*b*`
aab  aabb  aba  abba  abcba
@ print(g`a*b*`)
['aab', 'aabb', 'abba', 'abcba', 'aba']
@ len(g`a*b*`)
5

Regular Expression Globbing

If you have ever felt that normal globbing could use some more octane, then regex globbing is the tool for you! Any string that uses backticks (`) instead of quotes (', ") is interpreted as a regular expression to match filenames against. Like with regular globbing, a list of successful matches is returned. In Python-mode, this is just a list of strings. In subprocess-mode, each filename becomes its own argument to the subprocess command.

Let’s see a demonstration with some simple filenames:

@ touch a aa aaa aba abba aab aabb abcba
@ ls `a(a+|b+)a`
aaa  aba  abba
@ print(`a(a+|b+)a`)
['aaa', 'aba', 'abba']
@ len(`a(a+|b+)a`)
3

This same kind of search is performed if the backticks are prefaced with r. So the following expressions are equivalent: `test` and r`test`.

Other than the regex matching, this functions in the same way as normal globbing. For more information, please see the documentation for the re module in the Python standard library.

Formatted Glob Literals

Using the f modifier with either regex or normal globbing makes the glob pattern behave like a formatted string literal. This can be used to substitute variables and other expressions into the glob pattern:

@ touch a aa aaa aba abba aab aabb abcba
@ mypattern = 'ab'
@ print(f`{mypattern[0]}+`)
['a', 'aa', 'aaa']
@ print(gf`{mypattern}*`)
['aba', 'abba', 'abcba']

Match Globbing

The m modifier enables match globbing — a regex glob that returns capture groups instead of full paths. This is useful for extracting parts of matched paths directly:

@ for parent, name in m`tests/(.*)/(test_.*\.py)`:
      print(parent, name)
completers test_python.py
completers test_path_completers.py
procs test_specs.py
procs test_pipes.py

With a single capture group, a flat list of strings is returned:

@ m`xonsh/(.*\.py)`.sorted().files()
['__init__.py', '__main__.py', 'aliases.py']

See Globbing for the full m glob reference and XonshList methods.

Custom Path Searches

In addition, if normal globbing and regular expression globbing are not enough, xonsh allows you to specify your own search functions.

A search function is defined as a function of a single argument (a string) that returns a list of possible matches to that string. Search functions can then be used with backticks with the following syntax: @<name>`test`

The following example shows the form of these functions:

@ def foo(s):
      return [i for i in os.listdir('.') if i.startswith(s)]
@ @foo`aa`
['aa', 'aaa', 'aab', 'aabb']

Path Output

Using the p modifier with either regex or glob backticks changes the return type from a list of strings to a list of pathlib.Path objects:

@ p`.*`
[Path('foo'), Path('bar')]
@ [x for x in pg`**` if x.is_symlink()]
[Path('a_link')]

Path Literals

Path objects can be instantiated directly using p-string syntax. Path objects can be converted back to plain strings with str(), and this conversion is handled implicitly in subprocess mode.

@ mypath = p'/foo/bar'
@ mypath
Path('/foo/bar')
@ mypath.stem
'bar'
@ echo @(mypath)
/foo/bar
@ pwd
/home/snail

@ with p'/tmp'.cd():
      pwd
/tmp

@ with p'/tmp/newdir'.mkdir(mode=0o777, parents=True, exist_ok=True).cd():
      pwd
/tmp/newdir

@ p'/tmp/new.txt'.touch().chmod(0o700).write_text('hello')

Path object allows do some tricks with paths. Globbing certain path, checking and getting info:

@ mypath = p'/etc'
@ sorted(mypath.glob('**/*xonshrc*'))
[Path('/etc/xonsh/xonshrc'), Path('/etc/xonsh/rc.d/xonshrc.xsh')]
@ [mypath.exists(), mypath.is_dir(), mypath.is_file(), mypath.parent, mypath.owner()]
[True, True, False, Path('/'), 'root']

Aliases

Another important xonsh built-in is the aliases mapping. This is like a dictionary that affects how subprocess commands are run. If you are familiar with the POSIX shells alias built-in, this is similar. Alias command matching only occurs for the first element of a subprocess command.

Register an Alias

The keys of aliases are strings that act as commands in subprocess-mode. The values are:

  • A list of strings where the first element is the command and the remaining elements are its arguments.

  • A simple string that is automatically converted into a list using xonsh’s Lexer.split() method.

  • A string representing a xonsh command that will be converted into an ExecAlias (details next).

  • A callable that will be used as a callable alias (details next).

@ aliases['ls']
['ls', '--color=auto', '-v']

@ aliases['e'] = 'echo echo'
@ aliases['ll'] = ['ls', '-la']

@ aliases |= {
    'g':   'git status -sb',
    'gp':  ['git', 'pull'],
    'gco': 'git checkout',
  }

If you were to run gco feature-fabulous with the above aliases in effect, the command would reduce to ['git', 'checkout', 'feature-fabulous'] before being executed.

Removing an alias is as easy as deleting the key from the alias dictionary:

@ del aliases['banana']

Alias to Modify Command

The best way to modify command on the fly is to use alias that returns modified command. One of the most interesting application is expanding an alias:

@ @aliases.register
  @aliases.return_command
  def _xsudo(args):
      """Sudo with expanding aliases."""
      return ['sudo', '--', *aliases.eval_alias(args)]

@ aliases['install'] = "apt install cowsay"
@ xsudo install
Password:
Install cowsay

Or implement logic to run the right command:

@ @aliases.register
  @aliases.return_command
  def _vi(args):
      """Universal vi editor."""
      if $(which vim 2>/dev/null):
          return ['vim'] + args
      else:
          return ['vi'] + args

@ vi file

See Return Command Aliases for the full reference.

Callable Aliases

Basic Callable Alias

A callable alias is a function (or callable object) with a specific signature that can be used as a subprocess, either directly or when registered as an alias.

Using directly with Python evaluation via @():

@ def mybox():
     print('apple')
     echo 'banana'

@ @(mybox) | grep ba
banana

Register callable as an alias:

@ @aliases.register('mybox')
  def _mybox():
     print('apple')
     echo 'banana'

@ mybox | grep ba
banana

@ aliases['hello'] = lambda: print(f'Hello world')
  hello
Hello world

ExecAlias

If the string is representing a block of xonsh code, the alias will be registered as an ExecAlias, which is a callable alias under the hood. This block of code will then be executed whenever the alias is run. The arguments are available in the list $args or by the index in $arg<n> environment variables.

@ aliases |= {
    'answer': 'echo @(21+21)',
    'piu':    'pip install -U @($args)',
    'cdls':   'cd $arg0 && ls',
  }

You need to add @($args) manually if you need arguments in ExecAlias:

@ aliases |= {
    'noargs': 'echo @("all args will be ignored")',
    'args':  'echo @("the arguments are:") @($args)',
  }
@ noargs 1 2 3
all args will be ignored
@ args 1 2 3
the arguments are: 1 2 3

These three definitions are equal:

@ @aliases.register
  def _answer():
      echo @(21+21)

@ aliases['answer'] = lambda: $[echo @(21+21)]

@ aliases['answer'] = 'echo @(21+21)'

Anonymous Aliases

As mentioned above, it is also possible to treat functions outside this mapping as aliases, by wrapping them in @(). For example:

@ @(_banana)
'My spoon is tooo big!'
@ echo "hello" | @(lambda args, stdin=None: stdin.read().strip() + ' ' + args[0] + '\n') world
hello world

Unthreadable Aliases

Usually, callable alias commands will be run in a separate thread so that they may be run in the background. However, some aliases may need to be executed on the thread that they were called from. This is mostly useful for interactive tools (vim, less, htop), debuggers and profilers. To make an alias run in the foreground, use the @aliases.unthreadable decorator:

@aliases.register
@aliases.unthreadable
def _mycmd(args, stdin=None):
    return 'In your face!'

Uncapturable Aliases

Also, callable aliases by default will be executed such that their output is captured (like most commands in xonsh that don’t enter alternate mode). However, some aliases may want to run alternate-mode commands themselves. Thus the callable alias can’t be captured without dire consequences (tm). To prevent this, you can declare a callable alias uncapturable. This is mostly useful for aliases that then open up text editors, pagers, or the like. To make an alias uncapturable, use the @aliases.uncapturable decorator. This is probably best used in conjunction with @aliases.unthreadable. For example:

@aliases.register
@aliases.uncapturable
@aliases.unthreadable
def _binvi(args, stdin=None):
    vi -b @(args)  # Edit binary files

Note that @() is required to pass the python list args to a subprocess command.

Click Integration

If the click package is installed, you can register a click command as a xonsh alias with @aliases.register_click_command. The aliases.click attribute exposes the click module itself, so @aliases.click.option(...) works without a separate import click. Both are loaded lazily on first access.

@ @aliases.register_click_command
  @aliases.click.option('--name', help='The person to greet.')
  @aliases.click.option('--count', default=1, help='Number of greetings.')
  def _hello(ctx, count, name):
      """Greets NAME for a total of COUNT times."""
      for i in range(count):
          print(name, file=ctx.stdout)

@ hello --count 3 --name World
World
World
World

The call forms mirror @aliases.register — bare, (), or with an explicit name. Inside the click callback, ctx is a click.Context subclass carrying the usual xonsh alias parameters as attributes (ctx.alias_args, ctx.stdin, ctx.stdout, ctx.env, and so on). See Callable Aliases for the full reference.

Command Decorators (Decorator Aliases)

In xonsh you can decorate the command to transform output into desired object:

@ $(@lines ls /)
['/bin', '/etc', '/home']

@ showcmd echo prefix$(@lines ls /)
['echo', 'prefix/bin', 'prefix/etc', 'prefix/home']

@ $(@paths ls /)
[Path('/bin'), Path('/etc'), Path('/home')]

@ $(@path pwd)
Path('/home/snail')

@ $(@json curl -s https://api.github.com/repos/xonsh/xonsh)['default_branch']
main

@ $(@jsonl echo '{"a":1}\n{"b":2}')
[{'a': 1}, {'b': 2}]

@ $(@yaml echo 'a: 1')
{'a': 1}

See the full list of command decorators in Aliases article or build the new one.

Using DecoratorAlias and SpecAttrDecoratorAlias and callable output_format you can convert subprocess command output into Python object with your own logic:

from xonsh.procs.specs import SpecAttrDecoratorAlias

aliases['@and'] = SpecAttrDecoratorAlias(
                    {"output_format": lambda lines: ' and '.join([l.strip() for l in lines])},
                    "Join lines with 'and'.")

Now you can run:

@ $(@and ls /)
'/bin and /etc and /home'

Aliasing is a powerful way that xonsh allows you to seamlessly interact to with Python and subprocess. See Callable Aliases for the full callable aliases reference including stream capturing, env overlay, and return values.

Warning

If FOREIGN_ALIASES_OVERRIDE environment variable is False (the default), then foreign shell aliases that try to override xonsh aliases will be ignored. The setting of this environment variable must happen outside if xonsh, i.e. in the process that starts xonsh.

Prompt

Up, Down, Tab Completion

The up and down keys search history matching from the start of the line.

Tab completion is present as well. By default, in Python-mode you are able to complete based on the variable names in the current builtins, globals, and locals, as well as xonsh languages keywords & operator, files & directories, and environment variable names. In subprocess-mode, you additionally complete on the names of executable files on your $PATH, alias keys, and various additional completers.

xonsh also provides a means of modifying the behavior of the tab completer. More detail is available on the Tab Completion page.

Customizing the Prompt

Customizing the prompt by modifying $PROMPT, $RIGHT_PROMPT or $BOTTOM_TOOLBAR is probably the most common reason for altering an environment variable.

Note

Note that the $PROMPT variable will never be inherited from a parent process (regardless of whether that parent is a foreign shell or an instance of xonsh).

The $PROMPT variable can be a string, or it can be a function (of no arguments) that returns a string. The result can contain keyword arguments, which will be replaced automatically:

@ $PROMPT = '{user}@{hostname}:{cwd} @ '
snail@home:~ @ # it works!
@ $PROMPT = lambda: '{user}@{hostname}:{cwd} @> '
snail@home:~ @> # so does that!

See Customizing the Prompt in the Prompt Toolkit page for the full list of available prompt variables, custom PROMPT_FIELDS, conditional formatting, and virtual environment settings.

Colors

Xonsh supports colored output in prompts and print functions. Use color keywords like {GREEN} or {BOLD_BLUE} and {RESET} to clear:

@ print_color('{RED}Error:{RESET} something went wrong')
@ printx('Success!', 'BOLD_GREEN')

Colors work in prompts too:

@ $PROMPT = '{CYAN}{cwd}{RESET} @ '

See Prompt for the full list of color names, hex colors, and modifiers (bold, italic, underline, etc.).

Executing Commands and Scripts

When started with the -c flag and a command, xonsh will execute that command and exit, instead of entering the command loop.

Note

When executing commands this way your xonsh RC files are not applied.

@ xonsh -c "echo @(7+3)"
10

Longer scripts can be run either by specifying a filename containing the script, or by feeding them to xonsh via stdin. For example, consider the following script, stored in test.xsh:

#!/usr/bin/env xonsh

ls

print('removing files')
rm `file\d+.txt`

ls

print('adding files')
# This is a comment
for i, x in enumerate("xonsh"):
    echo @(x) > @("file{0}.txt".format(i))

print($(ls).replace('\n', ' '))

This script could be run by piping its contents to xonsh:

@ cat test.xsh | xonsh
file0.txt  file1.txt  file2.txt  file3.txt  file4.txt  test_script.sh
removing files
test_script.sh
adding files
file0.txt file1.txt file2.txt file3.txt file4.txt test_script.sh

or by invoking xonsh with its filename as an argument:

@ xonsh test.xsh
file0.txt  file1.txt  file2.txt  file3.txt  file4.txt  test_script.sh
removing files
test_script.sh
adding files
file0.txt file1.txt file2.txt file3.txt file4.txt test_script.sh

xonsh scripts can also accept command line arguments and parameters. These arguments are made available to the script in two different ways:

  1. In either mode, as individual variables $ARG<n> (e.g., $ARG1)

  2. In Python mode only, as a list $ARGS

For example, consider a slight variation of the example script from above that operates on a given argument, rather than on the string 'xonsh' (notice how $ARGS and $ARG1 are used):

#!/usr/bin/env xonsh

print($ARGS)

ls

print('removing files')
rm `file\d+.txt`

ls

print('adding files')
This is a comment
for i, x in enumerate($ARG1):
    echo @(x) > @("file{0}.txt".format(i))

print($(ls).replace('\n', ' '))
print()

@ xonsh test2.xsh snails
['test_script.sh', 'snails']
file0.txt  file1.txt  file2.txt  file3.txt  file4.txt  file5.txt  test_script.sh
removing files
test_script.sh
adding files
file0.txt file1.txt file2.txt file3.txt file4.txt file5.txt test_script.sh

@ echo @(' '.join($(cat @('file%d.txt' % i)).strip() for i in range(6)))
s n a i l s

Furthermore, you can also toggle the ability to print source code lines with the trace on and trace off commands. This is roughly equivalent to Python’s python -m trace.

Error Handling

Xonsh treats shell commands as first-class code. When a command fails, you usually want your script to stop instead of silently marching past the failure — the way a Python exception would — but you also want the flexibility of &&/|| short-circuit logic that the shell is built around.

By default, execution stops as soon as a command chain ends in a failing command. A chain is any group of commands whose result is determined together — a pipe, a logical &&/|| expression, or a bare single command. It is the final result of the chain that decides whether execution continues; individual commands that are explicitly rescued by || are not fatal.

A couple of examples:

@ echo hi | grep x                  # pipe chain — grep didn't match → raise
@ ls nofile && echo never           # && chain — ls failed → raise, echo skipped
@ ls nofile || echo rescued         # || chain — rescued by echo, no raise
rescued
@ (echo 1 && ls /etc) || echo fb    # nested — inner chain succeeded, no raise

The only subprocess form that does not stop execution on failure is the full-capture operator !(...): it returns a CommandPipeline object and leaves error handling entirely up to you. This is the idiomatic way to inspect a command’s result without triggering an exception:

@ if !(ls nofile):
      print("found")
  else:
      print("absent")

See Subprocess Error Handling for the full rules, including @error_raise/@error_ignore decorators, the environment variables that tune this behavior, and how the interactive prompt displays (or hides) the resulting exception.

Importing Xonsh (*.xsh)

You can import xonsh source files with the *.xsh file extension using the normal Python syntax:

from mine import *

Compile, Evaluate, & Execute

Xonsh provides built-in hooks to compile, evaluate, and execute strings of xonsh code. To prevent this functionality from having serious name collisions with the Python built-in compile(), eval(), and exec() functions, the xonsh equivalents all append an ‘x’. So for xonsh code you want to use the compilex(), evalx(), and execx() functions. If you don’t know what these do, you probably don’t need them.

Help & Superhelp with ? & ??

Xonsh allows you to inspect objects with question marks. A single question mark (?) is used to display the normal level of help. Double question marks (??) are used to display a higher level of help, called superhelp. Superhelp usually includes source code if the object was written in pure Python.

@ int?
Convert a number or string to an integer, or return 0 if no arguments
are given.  If x is a number, return x.__int__().  For floating point
numbers, this truncates towards zero.

@ @.imp.json.loads??
def loads(s, *, cls=None, object_hook=None, parse_float=None,
   parse_int=None, parse_constant=None, object_pairs_hook=None, **kw):

@ @.imp.json?.loads?
<json help>
<json.loads help>

It works for subprocess commands as well. Behavior depends on whether the name is a binary on $PATH or an alias:

For a binary, ? prints just the resolved path; ?? additionally runs man:

@ whoami?
Resolved whoami: '/usr/bin/whoami'

@ whoami??
Resolved whoami: '/usr/bin/whoami'
Running man whoami
WHOAMI(1)                   General Commands Manual                  WHOAMI(1)
…

When the name does not resolve to any binary, ?? no longer falls through to man — the failed resolution is printed on its own line:

@ nosuch?
Resolved nosuch: None

For an alias, ? gives a short summary and ?? adds the docstring, threadable/capturable flags (when set), the source file location and — the new bit — the function source code for callable aliases, fetched via inspect.getsource:

@ ls?
Alias: ['ls', '-G']

@ xonfig?
Alias: <xonsh.xonfig.XonfigAlias>
Descr: Manage xonsh configuration.

Define a callable alias and ask for the super-help form:

@ # ~/.xonshrc
  @aliases.register
  def _greet(args):
      """Print a friendly greeting."""
      print("hello,", *args)

@ greet?
Alias: FuncAlias({'name': 'greet', 'func': '_greet', 'return_what': 'result'})
Descr: Print a friendly greeting.

@ greet??
Alias: FuncAlias({'name': 'greet', 'func': '_greet', 'return_what': 'result'})
Descr: Print a friendly greeting.
Source: /home/snail/.xonshrc:1
Code:
@aliases.register
def _greet(args):
    """Print a friendly greeting."""
    print("hello,", *args)

List-style aliases expand recursively through other aliases, and you can see where the leading token resolves on disk:

@ aliases['lst']  = ['ls', '-la']
@ aliases['lst2'] = ['lst', '/tmp']
@ lst2??
Alias: ['lst', '/tmp']
Expanded: ['ls', '-G', '-la', '/tmp']
Resolved ls: '/opt/homebrew/.../ls'

For callable aliases defined interactively in the REPL, inspect has no source file to read from (co_filename is <stdin>), so Code: is replaced with a <source unavailable> placeholder while Source: still shows where the function was declared.

That’s All, Folks

To leave xonsh, hit Ctrl-D, type EOF, type quit, or type exit. On Windows, you can also type Ctrl-Z.

@ exit

To exit from the xonsh script just call the exit(code) function.

Now it is your turn.

See also