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#!/usr/bin/env python3
import os
import re
import argparse
import sys
IFS = (" ", "\t", "\n")
class EOFException(Exception):
pass
class Argument():
def __init__(self, value: str, allow_expansion=True):
pass
def expand():
pass
class Pipeline():
def __init__(self, instructions: list=[]):
self.instructions = instructions
def execute(self):
for instruction in self.instructions:
instruction.execute()
class Instruction():
def __init__(self, tokens: list=[], stdout=None, stderr=None):
self.prog = tokens[0]
self.args = tokens[1:]
self.stdout = stdout
self.stderr = stderr
def execute(self):
cpid = os.fork()
if cpid == 0:
if self.stdout is not None:
fd = os.open(self.stdout, os.O_WRONLY)
os.dup2(sys.stdout.fileno(), fd)
if self.stderr is not None:
fd = os.open(self.stderr, os.O_WRONLY)
os.dup2(sys.stderr.fileno(), fd)
os.execvp(self.prog, [self.prog] + self.args)
else:
_, status = os.waitpid(cpid, 0)
return status
class AndInstruction(Instruction):
def __init__(self, instruction1: Instruction, instruction2: Instruction):
self.instruction1 = instruction1
self.instruction2 = instruction2
def execute(self):
status = self.instruction1.execute()
if os.WIFEXITED(status) and os.WEXITSTATUS(status) == 0:
return self.instruction2.execute()
class OrInstruction(Instruction):
def __init__(self, instruction1: Instruction, instruction2: Instruction):
self.instruction1 = instruction1
self.instruction2 = instruction2
def execute(self):
status = self.instruction1.execute()
if not os.WIFEXITED(status) or not os.WEXITSTATUS(status) == 0:
return self.instruction2.execute()
class PipelineParser():
def read_escaped(self, string_iterator):
return next(string_iterator)
def read_literal(self, string_iterator):
literal = ""
while True:
c = next(string_iterator)
if c != "'":
literal += c
else:
return literal
def read_quoted(self, string_iterator):
# TODO handle substitutions
quoted = ""
while True:
c = next(string_iterator)
if c == "\\":
quoted += self.read_escaped(string_iterator)
elif c != '"':
quoted += c
else:
return quoted
def get_next_token(self, string_iterator):
token = None
while True:
try:
c = next(string_iterator)
except StopIteration:
break
# Skip leading whitespaces
if token is None and c in IFS:
continue
elif token is None:
token = ""
if c == "'":
token += self.read_literal(string_iterator)
elif c == "\\":
token += self.read_escaped(string_iterator)
elif c == "\"":
token += self.read_quoted(string_iterator)
elif c in IFS:
return token
else:
token += c
return token
def tokenize(self, string_iterator):
while True:
token = self.get_next_token(string_iterator)
if token is None:
break
yield token
def parse(self, line):
tokens = list(self.tokenize(iter(line)))
return Pipeline([Instruction(tokens)])
def read_next_pipeline(fh):
# TODO Support multiple pipelines per line
# TODO Support instructions spawning multiple lines
parser = PipelineParser()
while True:
line = fh.readline()
if line == "":
raise EOFException()
line = line.strip()
# We ignore empty lines and lines which start with #
if not line.startswith("#") and not line == "":
break
return parser.parse(line)
def main(arguments):
for script in arguments["<script>"]:
with open(script, mode="r", encoding="utf-8") as fh:
while True:
try:
pipeline = read_next_pipeline(fh)
pipeline.execute()
except EOFException:
break
if __name__ == "__main__":
parser = argparse.ArgumentParser(description="Command interpreter written in Python.")
parser.add_argument("<script>", action="store", nargs="+", help="Script to run")
args = parser.parse_args()
main(vars(args))
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