我有一个解析给定命令并将所有参数/程序分配给结构体的程序。在执行命令的主程序中，如果给出">"，我尝试将管道命令的输出重定向到文件。例如，我的程序将成功执行以下命令：
cat filea | grep pattern
但我也希望能够执行该命令
cat filea | grep pattern > outfile
作为一个附注，了解cmdscan.c的确切机制并不是非常重要，因为它被作为一种辅助程序提供，以帮助解析命令字符串并填充结构值，这使得在主程序hsh.c中检查情况更容易。此外，argv1和argv2是管道的左侧和右侧，因此只有当存在管道时argv2才会被填充。如果有任何形式的重定向，则文件名将存储在infile/outfile中，具体取决于重定向的方向。
这是我的主程序hsh.c，用于执行命令：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/fcntl.h>
#include <string.h>
#define BUFSIZE 500
struct cmd
{
int redirect_in; /* Any stdin redirection? */
int redirect_out; /* Any stdout redirection? */
int redirect_append; /* Append stdout redirection? */
int background; /* Put process in background? */
int piping; /* Pipe prog1 into prog2? */
char *infile; /* Name of stdin redirect file */
char *outfile; /* Name of stdout redirect file */
char *argv1[10]; /* First program to execute */
char *argv2[10]; /* Second program in pipe */
};
int cmdscan(char *cmdbuf, struct cmd *com);
int main() {
char buf[BUFSIZE];
struct cmd command;
pid_t pid;
int status;
int fd[2];
pipe(fd);
int fdout;
while((fgets(buf,BUFSIZE,stdin) != NULL)) {
if(cmdscan(buf,&command)==-1) {
printf("illegal format\n");
continue;
}
if((pid=fork()) <0)
perror("fork error\n");
if(strcmp(command.argv1[0],"exit") == 0) {
return 0;
}
else if (pid == 0) {
//if the command has piping
if(command.piping){
if((pid = fork()) <0)
perror("fork error");
//fork again so we can do more commands after this one
else if(pid == 0) {
if((pid = fork()) < 0)
perror("fork error");
else if (pid == 0){
//fdout = open(command.outfile, O_CREAT | O_WRONLY);
//dup2(fdout, STDOUT_FILENO);
dup2(fd[1], STDOUT_FILENO);
close(fd[1]);
execvp(*command.argv1,command.argv1);
} else {
dup2(fd[0],STDIN_FILENO);
close(fd[0]);
execvp(*command.argv2,command.argv2);
}
}
//execute normal command
}else {
//if normal command has redirection
if(command.redirect_out){
fdout = open(command.outfile, O_CREAT | O_WRONLY);
dup2(fdout,STDOUT_FILENO);
close(fd[0]);
execvp(*command.argv1,command.argv1);
}
else{
execvp(*command.argv1,command.argv1);
}
}
//..
exit(0);
} else {
if(wait(&status)!=pid)
perror("wait error");
}
}
return 0;
}
这是解析命令行的程序cmdscan.c。
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
struct cmd
{
int redirect_in; /* Any stdin redirection? */
int redirect_out; /* Any stdout redirection? */
int redirect_append; /* Append stdout redirection? */
int background; /* Put process in background? */
int piping; /* Pipe prog1 into prog2? */
char *infile; /* Name of stdin redirect file */
char *outfile; /* Name of stdout redirect file */
char *argv1[10]; /* First program to execute */
char *argv2[10]; /* Second program in pipe */
};
#define TRUE 1
#define FALSE 0
int
cmdscan(char *cmdbuf, struct cmd *com)
{
char *token;
char *curcmd; /* pointer to current command string */
char swtch[256]; /* buffer to hold copy of switch */
char *separators = " \t\n";
int i;
com->redirect_in = FALSE;
com->redirect_out = FALSE;
com->redirect_append = FALSE;
com->background = FALSE;
com->piping = FALSE;
if ( (com->argv1[0] = strtok(cmdbuf,separators) ) == NULL)
return(-1);
i = 1;
while( (com->argv1[i++] = (token = strtok(NULL,separators))) != NULL && strcmp(token,">") &&
strcmp(token,"<") && strcmp(token,">>") && strcmp(token,"&") && strcmp(token,"|") );
com->argv1[i-1] = NULL;
if ( token != NULL && strcmp(token,"|") == 0 )
{
com->piping = TRUE;
i = 0;
while( (com->argv2[i++] = (token = strtok(NULL,separators))) != NULL && strcmp(token,">") &&
strcmp(token,"<") && strcmp(token,">>") && strcmp(token,"&") && strcmp(token,"|") );
com->argv2[i-1] = NULL;
if ( com->argv2[0] == NULL )
return(-1);
}
while ( token != NULL ){
if ( !strcmp(token,">") || !strcmp(token,">>") )
{
if ( com->redirect_out )
return(-1);
com->redirect_out = TRUE;
if ( !strcmp(token,">>") )
com->redirect_append = TRUE;
if ( (com->outfile = strtok(NULL,separators)) == NULL )
return(-1);
}
else if ( !strcmp(token,"<") )
{
if ( com->redirect_in )
return(-1);
com->redirect_in = TRUE;
if ( (com->infile = strtok(NULL,separators)) == NULL )
return(-1);
}
else if ( !strcmp(token,"|") )
{
if ( com->piping )
return(-1);
}
else if ( !strcmp(token,"&") )
{
if ( com->background )
return(-1);
com->background = TRUE;
if ( (token = strtok(NULL,separators)) != NULL )
return(-1);
break;
}
else
return(-1);
token = strtok(NULL,separators);
}
return(0);
}
我尝试应用与重定向的简单命令相同的逻辑，但无法使其正常工作，并对管道感到有点困惑。
cat filea 2>&1 | grep pattern这样的命令，它在通过管道传递之前将 stderr 重定向到 stdout？ - user229044