Question

With the following Grammar, I get a syntax error with this sort of input:

ls /home > foo #Runs and works okay, but raises error token
ls /home /foo /bar /etc #works okay

I think it may have something to do with how lookahead works, but this is my first grammar and I am a bit confused about why it doesn’t work this way: external_cmd GT WORD is a redirect, redirect is a command, command is a commands, so input commands NEWLINE should work.

Top Rules of the Grammar:

input:
    error NEWLINE {
        printf("Error Triggered\n");
        yyclearin;
        yyerrok; 
        prompt(); 
    } |
    input NEWLINE {
        prompt();
    } | 
    input commands NEWLINE {
        prompt (); 
    } | 
    /* empty */
    ;   

commands: 
    command |   
    command SEMI | 
    command SEMI commands
    ;   

command:
    builtin_cmd |
    redirect |
    external_cmd { 
        execute_command($1, 0, NULL);
    }
    ;

redirect:
    external_cmd GT WORD  {
        printf("Redirecting stdout of %s to %s\n", $1->cmd, $3);
        //printf("DEBUG: GT\n");
        execute_command($1, STDOUT_FILENO, $3);
    }
    external_cmd LT WORD {
        printf("Redirecting stin of %s to %s\n", $1->cmd, $3);
        //printf("DEBUG: GT\n");
        execute_command($1, STDIN_FILENO, $3);
    }
    ;

The debug / verbose input of when the error token is raised:

Next token is token WORD ()
Shifting token WORD ()
Entering state 6
Reading a token: Next token is token WORD ()
Shifting token WORD ()
Entering state 24
Reading a token: Next token is token GT ()
Reducing stack by rule 22 (line 115):
   $1 = token WORD ()
-> $$ = nterm arg_list ()
Stack now 0 2 6
Entering state 26
Reducing stack by rule 19 (line 91):
   $1 = token WORD ()
   $2 = nterm arg_list ()
-> $$ = nterm external_cmd ()
Stack now 0 2
Entering state 16
Next token is token GT ()
Shifting token GT ()
Entering state 29
Reading a token: Next token is token WORD ()
Shifting token WORD ()
Entering state 33
Reducing stack by rule 11 (line 68):
Redirecting stdout of ls to foo
DEBUG: redirect mode is 1
DEBUG: Command to run is ls
DEBUG: Adding Argument /home
admin  kbrandt  tempuser
-> $$ = nterm @1 ()
Stack now 0 2 16 29 33
Entering state 34
Reading a token: Next token is token NEWLINE ()
syntax error
Error: popping nterm @1 ()
Stack now 0 2 16 29 33
Error: popping token WORD ()
Stack now 0 2 16 29
Error: popping token GT ()
Stack now 0 2 16
Error: popping nterm external_cmd ()
Stack now 0 2
Error: popping nterm input ()
Stack now 0
Shifting token error ()
Entering state 1
Next token is token NEWLINE ()
Shifting token NEWLINE ()
Entering state 3
Reducing stack by rule 1 (line 38):
   $1 = token error ()
   $2 = token NEWLINE ()
Error Triggered
-> $$ = nterm input ()
Stack now 0
Entering state 2

Update:
external_cmd is:

external_cmd:
    WORD arg_list {
        $$ = malloc( sizeof(struct ext_cmd) );
        if ( $$ == NULL)
            printf("Memory Allocation Error\n");
        $$->cmd = $1;
        $$->args_pp = $2;
    } |
    WORD    {
        $$ = malloc( sizeof(struct ext_cmd) );
        if ( $$ == NULL)
            printf("Memory Allocation Error\n");
        $$->cmd = $<string>1;
        $$->args_pp = NULL;
    }

Answer 1

Found it, in my redirect rule there is a missing pipe, so instead of two components, there is one with a mid-rule action, which is not what I want.