1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
#!/usr/bin/env python3
import os
import re
import argparse
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=[]):
self.prog = tokens[0]
self.args = tokens[1:]
def execute(self):
cpid = os.fork()
if cpid == 0:
os.execvp(self.prog, [self.prog] + self.args)
else:
os.waitpid(cpid, 0)
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))
|
