sys

The sys library provides access to system-specific parameters and functions: platform identification, command-line arguments, stdin, and interpreter exit: similar to Python’s sys module.

Available Functions

Constants

Functions

exit(code=0)

Raise a SystemExit exception to exit the interpreter. Unlike most exceptions, SystemExit cannot be caught by try/except blocks: it bypasses all except clauses and propagates to the caller (CLI, REPL, etc.). finally blocks still execute before it propagates. To handle errors gracefully instead of exiting, use raise() with a message.

Parameters:

• code (int/str, optional): Exit status. Default: 0. An integer produces the message "SystemExit: <code>"; a string is used as the message directly (and implies exit code 1).

Returns: None: does not return; propagates a SystemExit exception to the caller.

import sys

# Exit successfully (raises SystemExit: 0)
sys.exit()

# Exit with error code (raises SystemExit: 1)
sys.exit(1)

# Exit with a custom message
sys.exit("Fatal error occurred")

# except does NOT catch sys.exit(), but finally still runs:
try:
    sys.exit(42)
except Exception as e:
    print("This will never print - except is bypassed!")
finally:
    print("This WILL print - finally executes")

input(prompt=None)

Read a line from stdin, stripping the trailing newline. Only available when the environment is configured with a stdin reader (piped input via the CLI, or an io.Reader passed to RegisterSysLibrary in Go). The optional prompt argument is accepted but not printed: there is no interactive terminal in remote/server environments.

Parameters:

• prompt (str, optional): Ignored placeholder for Python compatibility. Default: None.

Returns: str: the line read from stdin, without its trailing newline. Returns "" at EOF.

line = input()
print("You typed:", line)

stdin

A file-like object connected to standard input. Only available when stdin is configured: either when running via the CLI with piped input, or when an input reader is supplied during registration of the sys library via the Go API.

sys.stdin is also iterable: each iteration yields one line including its trailing newline.

import sys

# Read all at once
data = sys.stdin.read()

# Read line by line
line = sys.stdin.readline()

# Iterate over lines
for line in sys.stdin:
    print("Got:", line.rstrip())

platform

A string identifying the operating system platform.

import sys
print(sys.platform)  # "darwin", "linux", or "win32"

version

A string containing the version of the Scriptling interpreter.

import sys
print(sys.version)  # "Scriptling 1.0"

maxsize

The maximum value of a signed integer (int64).

import sys
print(sys.maxsize)  # 9223372036854775807

path_sep

The path separator used by the operating system.

import sys
print(sys.path_sep)  # "/" on Unix, "\" on Windows

argv

A list of command-line arguments passed to the script.

import sys

if len(sys.argv) < 2:
    print("Usage: script.py <input_file>")
    sys.exit(1)

input_file = sys.argv[1]
print(f"Processing {input_file}")

In server modes (--server, --json-rpc, --mcp-tools, --package), sys.argv is available in every evaluator — the setup script, MCP tool handlers, HTTP route handlers, and JSON-RPC method handlers. Positional arguments after -- on the CLI are included, so app bundles can accept their own flags:

# --bundles is not a scriptling flag; it passes through to sys.argv
scriptling --package ./myapp -- --bundles /data

# Inside a tool or handler — each call resolves sys.argv fresh
import sys
bundles = "/data"
for i in range(len(sys.argv) - 1):
    if sys.argv[i] == "--bundles":
        bundles = sys.argv[i + 1]

Security Considerations

This is an extended library, requiring registration in Go, see Library Registration.

sys exposes whatever argv and stdin the embedder passes to RegisterSysLibrary(p, argv, stdin): if those contain secrets, a script can read them. Never register this library (or pass sensitive argv/env) for untrusted code. See the Security Guide.

Python Compatibility

This library implements a subset of Python’s sys module:

See Also

• subprocess: Spawn external commands
• os: Environment variables and filesystem access