When I am writing my own interpreter... Post: 302141149

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Top Forums Programming When I am writing my own interpreter... Post 302141149 by Legend986 on Thursday 18th of October 2007 12:26:22 AM

10-18-2007

Registered User

Yeah sure... I might seem a little ambitious and I'm sure it'll take some time to build all that but I'll show it to you once I'm done with it... So do you have any suggestions to give me as far as my last post is concerned? I've just pasted the relevant matter here:

And while implementing pipes, when I issue a command such as "ls | grep .c" in my interpreter, after parsing it, what should I be doing? I read about file descriptors and am assuming the following has to be done:

1. Parse the command line
2. argv[0] contains ls, so fork a process and execute it but redirect the output to a file (I don't know how this can be done internally in the C Code. I know I need to use the execv command to execute but how will I redirect?)
3. In the next parse, I scan the "|" character and so I know that the user wants to pipe the output and at this stage I would fork another process with the argv[2] string i.e. "grep .c" (but this will be stored in argv[2] and argv[3]. How will I know that the second one has command line arguments too and how should I handle them?) and then direct the output of this to the stdout.

Legend986

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LEARN ABOUT FREEBSD

atf-sh

ATF-SH(1)						    BSD General Commands Manual 						 ATF-SH(1)

NAME

     atf-sh [-s shell] -- interpreter for shell-based test programs

SYNOPSIS

     atf-sh script

DESCRIPTION

     atf-sh is an interpreter that runs the test program given in script after loading the atf-sh(3) library.

     atf-sh is not a real interpreter though: it is just a wrapper around the system-wide shell defined by ATF_SHELL.  atf-sh executes the inter-
     preter, loads the atf-sh(3) library and then runs the script.  You must consider atf-sh to be a POSIX shell by default and thus should not
     use any non-standard extensions.

     The following options are available:

     -s shell	  Specifies the shell to use instead of the value provided by ATF_SHELL.

ENVIRONMENT

     ATF_LIBEXECDIR    Overrides the builtin directory where atf-sh is located.  Should not be overridden other than for testing purposes.
     ATF_PKGDATADIR    Overrides the builtin directory where libatf-sh.subr is located.  Should not be overridden other than for testing purposes.
     ATF_SHELL	       Path to the system shell to be used in the generated scripts.  Scripts must not rely on this variable being set to select a
		       specific interpreter.

EXAMPLES

     Scripts using atf-sh(3) should start with:

	   #! /usr/bin/env atf-sh

     Alternatively, if you want to explicitly choose a shell interpreter, you cannot rely on env(1) to find atf-sh.  Instead, you have to hardcode
     the path to atf-sh in the script and then use the -s option afterwards as a single parameter:

	   #! /path/to/bin/atf-sh -s/bin/bash

ENVIRONMENT

     ATF_SHELL	  Path to the system shell to be used in the generated scripts.

SEE ALSO

     atf-sh(3)

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