我的shell中的联接运算符“;”无法正常工作

Question

I've written a simple shell in C, and I'm trying to get the ";" operator working properly, which would be the user typing command1 ; command2 into the command line and the shell executes the first command, followed by the second command. However, it seems that, for whatever reason, it is only executing the second command. Anyone have an idea why?

Here is that particular section of my code:

char* next = strchr(cmd, ';');

while (next != NULL) {
    /* 'next' points to ';' */
    *next = '\0';
    input = run(cmd, input, first, 0);

    cmd = next + 1;
    next = strchr(cmd, ';');
    first = 0;
}

Answer 1

Here strchr() function return the value of character pointer after the semi-colon for me.

If the input is

ls ; ps

strchr() returns

; ps

as a result.

Use strtok() instead of strchr() , which is used to split the string as use required.

Something like following :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void) 
{
    char *str = malloc(20);
    char *tok = NULL;


    strcpy(str, "command1;command2");
    tok = strtok(str, ";");
    while (tok) 
    {
        printf("Token: %s\n", tok);
        tok = strtok(NULL, ";");
    }

    free(str);

    return 0;
}

See here

Answer 2

your code is working for me. Just have added the condition to handle the corner case. please check the code in below.

char* next = strchr(cmd, ';');
while (next != NULL) {
    /* 'next' points to ';' */
    *next = '\0';
    input = run(cmd, input, first, 0);
    printf ("%s\n",cmd );

    cmd = next + 1;
    next = strchr(cmd, ';');

    if (NULL ==next ){
     input = run(cmd, input, first, 0);
      printf ("%s\n",cmd );
    }
    first = 0;
}