管道有问题。我的程序是C语言中的Shell程序。我想执行例如ls | wc，但运行后得到的是：
ls：无法访问|：没有这样的文件或目录ls：无法访问wc：没有这样的文件或目录。
我做错了什么？
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#define MAX_CMD_LENGTH 100
#define MAX_NUM_PARAMS 10
int parsecmd(char* cmd, char** params) { //split cmd into array of params
int i,n=-1;
for(i=0; i<MAX_NUM_PARAMS; i++) {
params[i] = strsep(&cmd, " ");
n++;
if(params[i] == NULL) break;
}
return(n);
};
int executecmd(char** params) {
pid_t pid = fork(); //fork process
if (pid == -1) { //error
char *error = strerror(errno);
printf("error fork!!\n");
return 1;
} else if (pid == 0) { // child process
execvp(params[0], params); //exec cmd
char *error = strerror(errno);
printf("unknown command\n");
return 0;
} else { // parent process
int childstatus;
waitpid(pid, &childstatus, 0);
return 1;
}
};
int execpipe (char ** argv1, char ** argv2) {
int fds[2];
pipe(fds);
int i;
pid_t pid = fork();
for (i=0; i<2; i++) {
if (pid == -1) { //error
char *error = strerror(errno);
printf("error fork!!\n");
return 1;
} else
if (pid == 0) {
if(i ==0){
close(fds[1]);
dup2(fds[0], 0);
close(fds[0]);
execvp(argv1[0], argv1);
char *error = strerror(errno);
printf("unknown command\n");
return 0;
} else if(i == 1) {
close(fds[0]);
dup2(fds[1], 1);
close(fds[1]);
execvp(argv2[0], argv2);
char *error = strerror(errno);
printf("unknown command\n");
return 0;
}
} else { // parent process
int childstatus;
waitpid(pid, &childstatus, 0);
return 1;
}
} // end for
};
int main() {
char cmd[MAX_CMD_LENGTH+1];
char * params[MAX_NUM_PARAMS+1];
char * argv1[MAX_NUM_PARAMS+1];
char * argv2[MAX_NUM_PARAMS+1];
int k, y, x;
int f = 1;
while(1) {
printf("$"); //prompt
if(fgets(cmd, sizeof(cmd), stdin) == NULL) break; //read command, ctrl+D exit
if(cmd[strlen(cmd)-1] == '\n') { //remove newline char
cmd[strlen(cmd)-1] = '\0';
}
int j=parsecmd(cmd, params); //split cmd into array of params
if (strcmp(params[0], "exit") == 0) break; //exit
for (k=0; k <j; k++) { //elegxos gia uparksi pipes
if (strcmp(params[k], "|") == 0) {
f = 0; y = k;
printf("pipe found\n");
}
}
if (f==0) {
for (x=0; x<k; x++) {
argv1[x]=params[x];
}
int z = 0;
for (x=k+1; x< j; x++) {
argv2[z]=params[x];
z++;
}
if (execpipe(argv1, argv2) == 0) break;
} else if (f==1) {
if (executecmd(params) == 0) break;
}
} // end while
return 0;
}
答案 0 :(得分：1)
execv*过程不解释shell脚本字符串。它只是启动一个可执行文件并将一个参数数组传递给它。因此，它无法组织管道。
如果您需要执行“普通”shell命令，则可能需要使用system(char*)过程而不是execvp。
否则，如果您需要自己管道，可能需要用'|'解析字符串特殊字符并使用pipe（），fork（）和I / O重定向。像这里How to run a command using pipe?
答案 1 :(得分：1)
通过以下更正更新了您的代码。
for()调用后，删除了两次迭代的fork()循环。dup2调用父进程和子进程后，删除了管道FD的错误关闭。dup2()调用父和子的重复文件描述符，对齐需要运行的命令。基本上我需要交换execvp(argv2[0], argv2)和execvp(argv1[0], argv1)来电。break;语句，用于搜索竖线字符。更新的代码如下。
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#define MAX_CMD_LENGTH 100
#define MAX_NUM_PARAMS 10
int parsecmd(char* cmd, char** params) { //split cmd into array of params
int i,n=-1;
for(i=0; i<MAX_NUM_PARAMS; i++) {
params[i] = strsep(&cmd, " ");
n++;
if(params[i] == NULL) break;
}
return(n);
};
int executecmd(char** params) {
pid_t pid = fork(); //fork process
if (pid == -1) { //error
char *error = strerror(errno);
printf("error fork!!\n");
return 1;
} else if (pid == 0) { // child process
execvp(params[0], params); //exec cmd
char *error = strerror(errno);
printf("unknown command\n");
return 0;
} else { // parent process
int childstatus;
waitpid(pid, &childstatus, 0);
return 1;
}
};
int execpipe (char ** argv1, char ** argv2) {
int fds[2];
pipe(fds);
int i;
pid_t pid = fork();
if (pid == -1) { //error
char *error = strerror(errno);
printf("error fork!!\n");
return 1;
}
if (pid == 0) { // child process
close(fds[1]);
dup2(fds[0], 0);
//close(fds[0]);
execvp(argv2[0], argv2); // run command AFTER pipe character in userinput
char *error = strerror(errno);
printf("unknown command\n");
return 0;
} else { // parent process
close(fds[0]);
dup2(fds[1], 1);
//close(fds[1]);
execvp(argv1[0], argv1); // run command BEFORE pipe character in userinput
char *error = strerror(errno);
printf("unknown command\n");
return 0;
}
};
int main() {
char cmd[MAX_CMD_LENGTH+1];
char * params[MAX_NUM_PARAMS+1];
char * argv1[MAX_NUM_PARAMS+1] = {0};
char * argv2[MAX_NUM_PARAMS+1] = {0};
int k, y, x;
int f = 1;
while(1) {
printf("$"); //prompt
if(fgets(cmd, sizeof(cmd), stdin) == NULL) break; //read command, ctrl+D exit
if(cmd[strlen(cmd)-1] == '\n') { //remove newline char
cmd[strlen(cmd)-1] = '\0';
}
int j=parsecmd(cmd, params); //split cmd into array of params
if (strcmp(params[0], "exit") == 0) break; //exit
for (k=0; k <j; k++) { //elegxos gia uparksi pipes
if (strcmp(params[k], "|") == 0) {
f = 0; y = k;
printf("pipe found\n");
break;
}
}
if (f==0) {
for (x=0; x<k; x++) {
argv1[x]=params[x];
}
int z = 0;
for (x=k+1; x< j; x++) {
argv2[z]=params[x];
z++;
}
if (execpipe(argv1, argv2) == 0) break;
} else if (f==1) {
if (executecmd(params) == 0) break;
}
} // end while
return 0;
}
如果您只对我所做的更改感兴趣，请参阅以下代码与上述更新代码之间的区别：
--- original.c
+++ updated.c
@@ -4,6 +4,7 @@
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
+#include <sys/wait.h>
#define MAX_CMD_LENGTH 100
@@ -43,44 +44,36 @@
pipe(fds);
int i;
pid_t pid = fork();
- for (i=0; i<2; i++) {
if (pid == -1) { //error
char *error = strerror(errno);
printf("error fork!!\n");
return 1;
- } else
- if (pid == 0) {
- if(i ==0){
+ }
+ if (pid == 0) { // child process
close(fds[1]);
dup2(fds[0], 0);
- close(fds[0]);
- execvp(argv1[0], argv1);
+ //close(fds[0]);
+ execvp(argv2[0], argv2); // run command AFTER pipe character in userinput
char *error = strerror(errno);
printf("unknown command\n");
return 0;
- } else if(i == 1) {
+ } else { // parent process
close(fds[0]);
dup2(fds[1], 1);
- close(fds[1]);
- execvp(argv2[0], argv2);
+ //close(fds[1]);
+ execvp(argv1[0], argv1); // run command BEFORE pipe character in userinput
char *error = strerror(errno);
printf("unknown command\n");
return 0;
}
- } else { // parent process
- int childstatus;
- waitpid(pid, &childstatus, 0);
- return 1;
- }
- } // end for
};
int main() {
char cmd[MAX_CMD_LENGTH+1];
char * params[MAX_NUM_PARAMS+1];
- char * argv1[MAX_NUM_PARAMS+1];
- char * argv2[MAX_NUM_PARAMS+1];
+ char * argv1[MAX_NUM_PARAMS+1] = {0};
+ char * argv2[MAX_NUM_PARAMS+1] = {0};
int k, y, x;
int f = 1;
while(1) {
@@ -95,6 +88,7 @@
if (strcmp(params[k], "|") == 0) {
f = 0; y = k;
printf("pipe found\n");
+ break;
}
}
if (f==0) {