问题描述
我正在尝试在 C 中创建一个 shell。我想要做的一件事是让一个文件包含 stdout 的内容。例如，"echo "abcd" > filename" 将创建一个名为 filename 的文件，它将包含 "abcd"。我在实现 dup2 时遇到了问题，因此它打印 exec 的结果以便正确打印。我很感激专家的眼光来查看我的代码并告诉我我缺少什么。提前致谢。
/* ----------------------------------------------------------------- */
/* PROGRAM shell.c */
/* This program reads in an input line,parses the input line */
/* into tokens,and use execvp() to execute the command. */
/* ----------------------------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <stdbool.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
/* ----------------------------------------------------------------- */
/* FUNCTION parse: */
/* This function takes an input line and parse it into tokens. */
/* It first replaces all white spaces with zeros until it hits a */
/* non-white space character which indicates the beginning of an */
/* argument. It saves the address to argv[],and then skips all */
/* non-white spaces which constitute the argument. */
/* ----------------------------------------------------------------- */
void parse(char *line,char **argv)
{
while (*line != '\0') { /* if not the end of line ....... */
while (*line == ' ' || *line == '\t' || *line == '\n')
*line++ = '\0'; /* replace white spaces with 0 */
*argv++ = line; /* save the argument position */
while (*line != '\0' && *line != ' ' &&
*line != '\t' && *line != '\n')
line++; /* skip the argument until ... */
}
*argv = '\0'; /* mark the end of argument list */
}
/* ----------------------------------------------------------------- */
/* FUNCTION execute: */
/* This function receives a commend line argument list with the */
/* first one being a file name followed by its arguments. Then,*/
/* this function forks a child process to execute the command using */
/* system call execvp(). */
/* ----------------------------------------------------------------- */
void execute(char **argv)
{
pid_t pid;
int status;
if ((pid = fork()) < 0) { /* fork a child process */
printf("*** ERROR: forking child process Failed\n");
exit(1);
}
else if (pid == 0) { /* for the child process: */
if (execvp(*argv,argv) < 0) { /* execute the command */
printf("*** ERROR: exec Failed\n");
exit(1);
}
}
else { /* for the parent: */
while (wait(&status) != pid) /* wait for completion */
;
}
}
/* ----------------------------------------------------------------- */
/* The main program starts here */
/* ----------------------------------------------------------------- */
int lsh_cd(char **args)
{
if (args[1] == NULL) {
fprintf(stderr,"lsh: expected argument to \"cd\"\n");
} else {
if (chdir(args[1]) != 0) {
perror("lsh");
}
}
return 1;
}
void main(void)
{
char line[1024]; /* the input line */
char *argv[64]; /* the command line argument */
while (1) { /* repeat until done .... */
printf("Shell -> "); /* display a prompt */
gets(line); /* read in the command line */
printf("\n");
for(int i = 0; i < 64; i++)
{
argv[i] = "null";
}
parse(line,argv); /* parse the line */
if (strcmp(argv[0],"exit") == 0) {
/* is it an "exit"? */
exit(0);
}
/* makes all the values null if the arguments are null*/
for(int i = 0; i < 64; i++)
{
if(argv[i] == '\0'){
argv[i]= "null";
}
}
/* finds out the size of the arguments */
int sizeOfArgv = 0;
for(int i = 0; i < 64; i++)
{
if (strcmp(argv[i],"null") != 0) {
sizeOfArgv++;
}
}
/*finds out if the program has a > in it */
bool boolContains = false;
int x =0;
for(int j=0;j<sizeOfArgv;j++){
if(strcmp(argv[j],">") == 0){
boolContains = true;
x = j;
}
}
if (strcmp(argv[0],"cd") == 0) { /* exit if it is */
lsh_cd(argv);
}else if(boolContains){
char *argv2[x];
for(int t=0;t<x;t++){
argv2[t]=argv[t];
}
char str[80];
strcpy(str,argv[x+1]);
strcat(str,".txt");
int f = open(str,O_WRONLY | O_CREAT | O_Trunc);
dup2(f,1);
execute(argv2);
}
else{
execute(argv);
} /* otherwise,execute the command */
}
解决方法
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