爲什麼擴展grep不起作用？

Question

當我嘗試像這樣擴展grep時，它不起作用。

const char *grep[] = { "grep", "-E", "'JOBS|COMPIZ'" };

如果我這樣做，只是沒有單引號然後它一個字符串。爲什麼？爲什麼我不能像上面那樣構建擴展grep的參數？以下只有一個字符串正在工作。

const char *grep[] = { "grep", "-E", "JOBS" };

我的程序應該做printenv | sort | grep <parameter-list> | less，如果沒有參數主要然後程序應該做的printenv | sort | less。我已經實現了後者的功能，現在我需要實現參數列表的grep，但我似乎無法在C代碼中進行擴展grep。

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

struct command 
{ 
    const char **argv; 
}; 

int 
spawn_proc (int in, int out, struct command *cmd) 
{ 
    pid_t pid; 

    if ((pid = fork()) == 0) 
    { 
     if (in != 0) 
     { 
      dup2 (in, 0); 
      close (in); 
     } 

     if (out != 1) 
     { 
      dup2 (out, 1); 
      close (out); 
     } 

     return execvp (cmd->argv [0], (char * const *)cmd->argv); 
    } 

    return pid; 
} 

int 
fork_pipes (int n, struct command *cmd) 
{ 
    int i; 
    pid_t pid; 
    int in, fd [2]; 

    /* The first process should get its input from the original file descriptor 0. */ 
    in = 0; 

    /* Note the loop bound, we spawn here all, but the last stage of the pipeline. */ 
    for (i = 0; i < n - 1; ++i) 
    { 
     pipe (fd); 

     /* f [1] is the write end of the pipe, we carry `in` from the prev iteration. */ 
     spawn_proc (in, fd [1], cmd + i); 

     /* No need for the write and of the pipe, the child will write here. */ 
     close (fd [1]); 

     /* Keep the read end of the pipe, the next child will read from there. */ 
     in = fd [0]; 
    } 

    /* Last stage of the pipeline - set stdin be the read end of the previous pipe 
     and output to the original file descriptor 1. */ 
    if (in != 0) 
     dup2 (in, 0); 

    /* Execute the last stage with the current process. */ 
    return execvp (cmd [i].argv [0], (char * const *)cmd [i].argv); 
} 

int 
main (int argc, char ** argv) 
{ 
    printf("in main..."); 
    int i; 

    if (argc == 1) { 
     const char *printenv[] = { "printenv", 0}; 
     const char *sort[] = { "sort", 0 }; 
     const char *less[] = { "less", 0 }; 

     struct command cmd [] = { {printenv}, {sort}, {less} }; 
     return fork_pipes (3, cmd); 
    } 
    if (argc > 1) { 
    /*char *tmp = argv[1]; 
    sprintf(tmp, "%s%s", "'", tmp);*/ 
     for(i=1; i<argc-1; i++) 
     { 
      /* tmp = "%s%s%s", tmp, "\\|", argv[i]; 
      printf("tmp:%s", tmp); 
     sprintf(tmp, "%s%s%s", tmp, "|", argv[i]); 
     sprintf(tmp, "%s%s", tmp, "'");*/ 
     } 

     const char *printenv[] = { "printenv", 0}; 
     const char *grep[] = { "grep", "-E", "JOB" }; 
     const char *sort[] = { "sort", 0 }; 
     const char *less[] = { "less", 0 }; 

     struct command cmd [] = { {printenv}, {grep}, {sort}, {less} }; 
     return fork_pipes (4, cmd); 
    } 




} 

Answer 1

不要在參數中使用單引號。只有在命令行中才需要它們來防止shell解釋垂直條。