linecat.py

#!/usr/bin/env python3
import os
import sys
import textwrap


# https://github.com/coreutils/coreutils/commit/fcfba90d0d27a1bacf2020bac4dbec74ed181028
IO_BUFSIZE = 256 * 1024


def print_usage(argv0: str = "./linecat.py") -> None:
    print(
        textwrap.dedent(
            f"""\
        usage: {argv0} [FILE]...

        Write each line of FILE(s) or standard input shorter than PIPE_BUF to standard
        output, with a separate write per line. (This allows multiple linecat's to write
        to a single pipe simultaneously without interleaving within lines.) If a line is
        more than PIPE_BUF (usually 4096) bytes long, it is skipped and sent to stderr.\
            """
        )
    )


def main() -> None:
    try:
        argv0, *args = sys.argv
    except ValueError:
        print_usage()
        sys.exit(1)

    for i, arg in enumerate(args):
        if arg == "--":
            del args[i]
            break
        elif arg in ("-h", "--help"):
            print_usage(argv0)
            sys.exit(0)

    try:
        stdout_pipe_buf = os.fpathconf(sys.stdout.fileno(), "PC_PIPE_BUF")
    except (AttributeError, OSError, ValueError):
        stdout_pipe_buf = 512  # POSIX guaranteed minimum value

    stderr_isatty = sys.stderr.isatty()

    for path in args or ("-",):
        try:
            with sys.stdin.buffer if path == "-" else open(path, "rb", IO_BUFSIZE) as f:
                for line in f:
                    if len(line) > stdout_pipe_buf:
                        if stderr_isatty:
                            sys.stderr.buffer.raw.write(b"line too long: " + line)
                        else:
                            sys.stderr.buffer.raw.write(line)
                    else:
                        sys.stdout.buffer.raw.write(line)
        except FileNotFoundError:
            print(f"{argv0}: {path}: No such file or directory", file=sys.stderr)
            sys.exit(1)
        except OSError as e:
            print(f"{argv0}: {path}: {e.strerror}", file=sys.stderr)
            sys.exit(1)


if __name__ == "__main__":
    main()

License: CC0-1.0