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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tcl_getopenfile

Tcl_GetOpenFile(3)					      Tcl Library Procedures						Tcl_GetOpenFile(3)

__________________________________________________________________________________________________________________________________________________

NAME

       Tcl_GetOpenFile - Return a FILE* for a channel registered in the given interpreter (Unix only)

SYNOPSIS

       #include <tcl.h>

       int
       Tcl_GetOpenFile(interp, chanID, write, checkUsage, filePtr)

ARGUMENTS

       Tcl_Interp *interp (in)		   Tcl interpreter from which file handle is to be obtained.

       const char *chanID (in)		   String identifying channel, such as stdin or file4.

       int write (in)			   Non-zero means the file will be used for writing, zero means it will be used for reading.

       int checkUsage (in)		   If  non-zero,  then	an  error will be generated if the file was not opened for the access indicated by
					   write.

       ClientData *filePtr (out)	   Points to word in which to store pointer to FILE structure for the file given by chanID.
_________________________________________________________________

DESCRIPTION

       Tcl_GetOpenFile takes as argument a file identifier of the form returned by the open command and returns at *filePtr a pointer to the  FILE
       structure for the file.	The write argument indicates whether the FILE pointer will be used for reading or writing.  In some cases, such as
       a channel that connects to a pipeline of subprocesses, different FILE pointers will be returned for reading and	writing.   Tcl_GetOpenFile
       normally  returns TCL_OK.  If an error occurs in Tcl_GetOpenFile (e.g. chanID did not make any sense or checkUsage was set and the file was
       not opened for the access specified by write) then TCL_ERROR is returned and the interpreter's result will contain an  error  message.	In
       the current implementation checkUsage is ignored and consistency checks are always performed.

       Note that this interface is only supported on the Unix platform.

KEYWORDS

       channel, file handle, permissions, pipeline, read, write

Tcl									8.0							Tcl_GetOpenFile(3)