diff --git a/rbinstall/errors.py b/rbinstall/errors.py
new file mode 100644
index 0000000000000000000000000000000000000000..5cff053af13788885db4ccf32ebf6eb838720a36
--- /dev/null
+++ b/rbinstall/errors.py
@@ -0,0 +1,60 @@
+"""Errors for the installation process.
+
+Version Added:
+    1.0
+"""
+
+# NOTE: This file must be syntactically compatible with Python 3.7+.
+from __future__ import annotations
+
+from typing import List
+
+
+class InstallerError(Exception):
+    """A common error for the installation process.
+
+    Version Added:
+        1.0
+    """
+
+
+class RunCommandError(InstallerError):
+    """An error with running a command.
+
+    Version Added:
+        1.0
+    """
+
+    ######################
+    # Instance variables #
+    ######################
+
+    #: The full command line that was executed.
+    command: List[str]
+
+    #: The exit code of the process.
+    exit_code: int
+
+    def __init__(
+        self,
+        *,
+        command: List[str],
+        exit_code: int,
+    ) -> None:
+        """Initialize the error.
+
+        Args:
+            command (list of str):
+                The full command line that was executed.
+
+            exit_code (int):
+                The exit code of the process.
+        """
+        self.command = command
+        self.exit_code = exit_code
+
+        command_str = ' '.join(command)
+
+        super().__init__(
+            f'Error executing `{command_str}`: exit code {exit_code}'
+        )
diff --git a/rbinstall/process.py b/rbinstall/process.py
new file mode 100644
index 0000000000000000000000000000000000000000..b769d0dc8a48a5992abb3b2ab4cd11fde5740416
--- /dev/null
+++ b/rbinstall/process.py
@@ -0,0 +1,189 @@
+"""Utilities for working with processes and output.
+
+Version Added:
+    1.0
+"""
+
+# NOTE: This file must be syntactically compatible with Python 3.7+.
+from __future__ import annotations
+
+import os
+import subprocess
+import shlex
+import sys
+from typing import List, NoReturn, Optional, Sequence
+
+from typing_extensions import NotRequired, TypedDict
+
+from rbinstall.errors import RunCommandError
+
+
+DEBUG = (os.environ.get('RBINSTALL_DEBUG') == '1')
+
+
+class RunKwargs(TypedDict):
+    """Keyword arguments supported by the :py:func:`run` method.
+
+    See :py:func:`run` for documentation on these arguments.
+
+    Version Added:
+        1.0
+    """
+
+    capture_command: NotRequired[Optional[List[List[str]]]]
+    displayed_command: NotRequired[Optional[List[str]]]
+    dry_run: NotRequired[bool]
+    raw: NotRequired[bool]
+
+
+def die(
+    msg: str,
+) -> NoReturn:
+    """Print an error and exit.
+
+    Version Added:
+        1.0
+
+    Args:
+        msg (str):
+            The message to display.
+    """
+    sys.stderr.write(f'{msg}\n')
+    sys.exit(1)
+
+
+def debug(
+    msg: str,
+    *,
+    show_prefix: bool = True,
+) -> None:
+    """Output debug information.
+
+    This will only be shown if the :envvar:`RBINSTALL_DEBUG` environment
+    variable is set to ``1``.
+
+    Version Added:
+        1.0
+
+    Args:
+        msg (str, optional):
+            The message to display.
+    """
+    if DEBUG:
+        if show_prefix:
+            print(f'[DEBUG] {msg}')
+        else:
+            print(msg)
+
+
+def run(
+    command: List[str],
+    *,
+    capture_command: Optional[List[List[str]]] = None,
+    displayed_command: Optional[List[str]] = None,
+    dry_run: bool = False,
+    raw: bool = False,
+) -> None:
+    """Run an external command.
+
+    Output will be streamed.
+
+    Version Added:
+        1.0
+
+    Args:
+        command (list of str):
+            The full command line to run.
+
+        capture_command (list of list of str, optional):
+            If provided as a list, the command to run will be stored in the
+            list.
+
+        displayed_command (list of str, optional):
+            An optional command to show for display purposes, instead of the
+            actual command.
+
+        dry_run (bool, optional):
+            Whether to perform a dry-run of the command.
+
+            If ``True``, the command won't be executed.
+
+        raw (bool, optional):
+            Whether to execute with raw output to the terminal.
+
+    Raises:
+        rbinstall.errors.RunCommandError:
+            There was an error running the command.
+    """
+    if not displayed_command:
+        displayed_command = command
+
+    if capture_command is None:
+        debug('  $ %s' % join_cmdline(displayed_command),
+              show_prefix=False)
+    else:
+        capture_command.append(displayed_command)
+
+    if not dry_run:
+        if raw:
+            try:
+                subprocess.run(command, check=True)
+            except subprocess.CalledProcessError as e:
+                raise RunCommandError(command=command,
+                                      exit_code=e.returncode)
+        else:
+            with subprocess.Popen(command,
+                                  stdout=subprocess.PIPE,
+                                  stderr=subprocess.STDOUT) as p:
+                assert p.stdout is not None
+
+                stdout = sys.stdout
+                stdout_buffer = stdout.buffer
+
+                while p.poll() is None:
+                    stdout_buffer.write(p.stdout.read1())
+                    stdout.flush()
+
+                # Write anything remaining in the buffer.
+                stdout_buffer.write(p.stdout.read())
+                stdout.flush()
+
+                exit_code = p.poll()
+
+                debug(f'exit code = {exit_code}')
+
+                if exit_code != 0:
+                    assert exit_code is not None
+                    raise RunCommandError(command=command,
+                                          exit_code=exit_code)
+
+
+def join_cmdline(
+    cmdline: Sequence[str],
+) -> str:
+    """Return a string representation of a command line, joined from parts.
+
+    This is similar to :py:meth:`shlex.join`, but avoids quoting characters
+    such as ``|`` that might need to be represented as-is in command line
+    output.
+
+    Version Added:
+        1.0
+
+    Args:
+        cmdline (list of str):
+            The command line to join.
+
+    Returns:
+        str:
+        The resulting command line string.
+    """
+    parts: List[str] = []
+
+    for part in cmdline:
+        if part != '|':
+            part = shlex.quote(part)
+
+        parts.append(part)
+
+    return ' '.join(parts)