301 lines
8.0 KiB
Nim
301 lines
8.0 KiB
Nim
# fsh - Forka shell
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# 2021 - Seculum Forka
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# This program is licensed under the agpl v3.0 only license
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# imports
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import streams
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import osproc
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import strtabs
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import os
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import strutils
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# globals
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var shellVariables = newStringTable(modeCaseSensitive)
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# Environment variables get defined in a separate var
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var envVariables = newStringTable(modeCaseSensitive)
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# populate the table
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for k, v in envPairs():
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envVariables[k]=v
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# list of builtin commands
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let builtins: array[4, string] = [
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"set",
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"setenv",
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"echo",
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"exit",
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]
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# Exception types
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type
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ShellError= object of CatchableError
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line: int
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col: int
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whileExec: string
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ShellVariableError=object of ShellError
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variable: string
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ShellCommandError = object of ShellError
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command: string
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# forward declarations
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proc eval(cmd: string): string
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proc substitute(strm: Stream, delim = ";\p"): string
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# skipSpaces reads the stream until a non-space character is found
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proc skipSpaces(strm: Stream): int =
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while not strm.atEnd():
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if strm.peekChar() == ' ':
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discard strm.readChar()
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result.inc
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else: break
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# readLiterals parses the string passed in as a literal, preserving all braces except the first and last ones
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proc readLiteral(strm: Stream): string =
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var numbraces=1
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while not strm.atEnd() and numbraces > 0:
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let c = strm.readChar()
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case c:
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of '{':
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numbraces.inc
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of '}':
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numbraces = numbraces - 1
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of '\\':
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if strm.peekChar notin {'{', '}'}: result.add(strm.readChar)
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result.add(strm.readChar)
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else:
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result.add(c)
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# a forward declaration. Fuck this shit
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proc readSubstitution(strm: Stream): string
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# readInterpelation reads the interpelation in between [ and ]
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proc readInterpelation(strm: Stream): string =
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while not strm.atEnd():
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let c = strm.readChar()
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case c:
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of '{':
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result.add('{')
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result.add(strm.readLiteral)
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result.add('}')
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of '[':
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result.add('[')
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result.add(strm.readInterpelation)
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result.add(']')
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of '"':
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result.add("\"")
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result.add(strm.readSubstitution)
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result.add("\"")
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of '\\':
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result.add("\\")
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result.add(strm.readChar())
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of ']':
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break
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else: result.add(c)
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# readSubstitution reads a substitutionbetween "quotes"
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proc readSubstitution(strm: Stream): string =
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while not strm.atEnd():
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let c = strm.readChar()
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case c:
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of '{':
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result.add('{')
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result.add(strm.readLiteral)
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result.add('}')
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of '[':
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result.add('[')
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result.add(strm.readInterpelation)
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result.add(']')
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of '"':
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break
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of '\\':
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result.add("\\")
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result.add(strm.readChar())
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else: result.add(c)
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# readCommand reads a command from stream
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proc readCommand(strm: Stream): string =
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while not strm.atEnd():
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let c = strm.readChar()
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case c:
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of '{':
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result.add('{')
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result.add(strm.readLiteral)
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result.add('}')
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of '[':
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result.add('[')
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result.add(strm.readInterpelation)
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result.add(']')
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of '"':
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result.add("\"")
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result.add(strm.readSubstitution)
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result.add("\"")
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of '\\':
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result.add("\\")
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result.add(strm.readChar())
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of '\n', '\r', ';':
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break
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else: result.add(c)
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# readVariable reads a variable
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proc readVariable(strm: Stream): string =
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let c = strm.readChar()
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case c:
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of '{':
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result = strm.readLiteral()
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of '[':
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result.add(strm.readInterpelation)
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of '"':
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result.add(strm.readSubstitution())
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of ']', '}':
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stderr.write("Unexpected " & c & ".\n")
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else:
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result.add(c)
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while not strm.atEnd():
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let d = strm.readChar()
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case d:
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of 'a'..'z', 'A'..'Z', '0'..'9', '_', ':': result.add(d)
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else: break
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# evalVariable finds a value of a variable
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proc evalVariable(vari: string): string =
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if shellVariables.hasKey(vari):
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result=shellVariables[vari]
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elif envVariables.hasKey(vari):
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result = envVariables[vari]
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else:
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var e = newException(ShellVariableError, "No such variable: " & vari)
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e.variable = vari
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raise e
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# substitute does a substitution on the stream passed in
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proc substitute(strm: Stream, delim=";\p"): string =
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while not strm.atEnd():
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let c = strm.readChar()
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if c in delim: break
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case c:
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of '{':
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result.add(strm.readLiteral)
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of '}':
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stderr.write("Extra closing brace")
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of '[':
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result.add(strm.readInterpelation.eval)
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of ']':
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stderr.write("Extra closing bracket")
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of '\\':
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result.add(strm.readChar())
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of '$': result.add(strm.readVariable.evalVariable)
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of ';', '\n', '\r': break
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else:
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result.add(c)
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# parseCommand parses the string given into a list representing a command
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proc parseCommand(cmd: string): seq[string] =
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var newitem = ""
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let strm = newStringStream(cmd)
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while true:
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if strm.atEnd():
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result.add(newitem)
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break
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let c = strm.readChar()
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case c:
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of '{':
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newitem.add(strm.readLiteral)
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of '[':
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newitem.add(strm.readInterpelation.eval)
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of '"':
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newitem.add(strm.readSubstitution.newStringStream.substitute)
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of '$': result.add(strm.readVariable.evalVariable)
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of ' ':
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if (result == @[]) and (newitem == ""): continue
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result.add(newitem)
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newitem = ""
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discard strm.skipSpaces()
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of ';', '\n', '\r':
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result.add(newitem)
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break
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else: newitem.add(c)
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# runBuiltin runs a shell builtin
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proc runBuiltin(builtin: string, args: openArray[string]): string =
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case builtin:
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of "set":
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if args.len < 2:
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var e = newException(ShellCommandError, "Set: not enough arguments provided")
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e.command="set"
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raise e
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shellVariables[args[0]] = args[1..^1].join(" ")
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return ""
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of "setenv":
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if args.len < 2:
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raise newException(Exception, "setenv: Not enough arguments provided")
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try:
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envVariables[args[0]] = args[1..^1].join(":")
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putEnv(args[0], args[1..^1].join(":"))
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except OSError as e:
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raise newException(Exception, "setenv: " & e.msg)
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return ""
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of "echo":
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if args[0] == "-n":
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return args[1..^1].join(" ")
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return args.join(" ") & "\p"
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of "exit":
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if args.len == 0:
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quit(0)
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elif args.len == 1:
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try:
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quit(args[0].parseInt)
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except ValueError:
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quit(0)
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else:
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try:
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let exitcode=args[0].parseInt
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if exitcode > 0:
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stderr.write(args[1..^1].join(" "), "\p")
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else:
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stdout.write(args[1..^1].join(" "), "\p")
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quit(exitcode)
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except ValueError:
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stdout.write(args.join(" "), "\p")
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quit(0)
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else:
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raise newException(Exception, "Fsh: No such builtin implemented")
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# executes executes the command. For now it involves catting the command and printing it
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proc execute(cmd: string): int =
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let strm=cmd.newStringStream
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while not strm.atEnd:
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let parsed = strm.readCommand.parseCommand
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if parsed == @[]:
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continue
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let progname = parsed[0]
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let args = parsed[1..parsed.high]
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if progname in builtins:
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stdout.write(runBuiltin(progname, args))
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result = 0
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continue
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let ps = startProcess(progname, args=args, options={poUsePath, poParentStreams})
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result = ps.waitForExit
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ps.close
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strm.close
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# eval evaluates the given string
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proc eval(cmd: string): string =
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let strm=cmd.newStringStream
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while not strm.atEnd():
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let parsed = strm.readCommand.parseCommand
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if parsed == @[]:
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continue
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let progname=parsed[0]
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let args = parsed[1..parsed.high]
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if progname in builtins:
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result = runBuiltin(progname, args)
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continue
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let ps = startProcess(progname, args=args, options={poUsePath})
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result=ps.outputStream.readAll
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ps.close
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strm.close
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when isMainModule:
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let stdinstrm = stdin.newFileStream
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while not stdinstrm.atEnd():
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stdinstrm.readCommand.execute.echo
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