run_command.c

/* Runs command while optionally redirecting stdout,
 * stderr and stdin to a file prior and not
 * making any changes to the environment.
 *
 * Author: Grok
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

void print_help(const char *progname) {
    printf("Usage: %s [options] command [args...]\n", progname);
    printf("Run a command with optional redirected output/input, preserving the environment.\n\n");
    printf("Options:\n");
    printf("  --stdout <file>  Redirect stdout to <file>\n");
    printf("  --stderr <file>  Redirect stderr to <file>\n");
    printf("  --stdin <file>   Redirect stdin from <file>\n");
    printf("  --help           Show this help message and exit\n");
    printf("\nNotes:\n");
    printf("  - Options are optional and must appear before the command or '--'.\n");
    printf("  - If an option is not specified, the corresponding stream is not redirected.\n");
    printf("  - Use '--' to separate options from arguments that look like options.\n");
    printf("Example:\n");
    printf("  %s --stdout out.txt --stderr err.txt /bin/echo hello\n", progname);
    exit(0);
}

int main(int argc, char *argv[], char *envp[]) {
    const char *stdout_file = NULL;
    const char *stderr_file = NULL;
    const char *stdin_file = NULL;
    int i;
    int cmd_start = 0;

    // Parse arguments
    for (i = 1; i < argc; i++) {
        if (strcmp(argv[i], "--help") == 0) {
            print_help(argv[0]);
        } else if (strcmp(argv[i], "--") == 0) {
            cmd_start = i + 1;
            break;
        } else if (strcmp(argv[i], "--stdout") == 0) {
            if (i + 1 >= argc) {
                fprintf(stderr, "Error: --stdout requires a file argument\n");
                return 1;
            }
            stdout_file = argv[++i];
        } else if (strcmp(argv[i], "--stderr") == 0) {
            if (i + 1 >= argc) {
                fprintf(stderr, "Error: --stderr requires a file argument\n");
                return 1;
            }
            stderr_file = argv[++i];
        } else if (strcmp(argv[i], "--stdin") == 0) {
            if (i + 1 >= argc) {
                fprintf(stderr, "Error: --stdin requires a file argument\n");
                return 1;
            }
            stdin_file = argv[++i];
        } else {
            // Non-option argument; start of command
            cmd_start = i;
            break;
        }
    }

    // Check if a command was provided
    if (cmd_start == 0 || cmd_start >= argc) {
        fprintf(stderr, "No command specified\n");
        return 1;
    }

    // Redirect stdin if specified
    if (stdin_file) {
        int stdin_fd = open(stdin_file, O_RDONLY);
        if (stdin_fd == -1) {
            perror("Failed to open stdin file");
            return 1;
        }
        if (dup2(stdin_fd, STDIN_FILENO) == -1) {
            perror("Failed to redirect stdin");
            return 1;
        }
        close(stdin_fd);
    }

    // Redirect stdout if specified
    if (stdout_file) {
        int stdout_fd = open(stdout_file, O_WRONLY | O_CREAT | O_TRUNC, 0644);
        if (stdout_fd == -1) {
            perror("Failed to open stdout file");
            return 1;
        }
        if (dup2(stdout_fd, STDOUT_FILENO) == -1) {
            perror("Failed to redirect stdout");
            return 1;
        }
        close(stdout_fd);
    }

    // Redirect stderr if specified
    if (stderr_file) {
        int stderr_fd = open(stderr_file, O_WRONLY | O_CREAT | O_TRUNC, 0644);
        if (stderr_fd == -1) {
            perror("Failed to open stderr file");
            return 1;
        }
        if (dup2(stderr_fd, STDERR_FILENO) == -1) {
            perror("Failed to redirect stderr");
            return 1;
        }
        close(stderr_fd);
    }

    // Detach from terminal
    if (setsid() == -1) {
        perror("Failed to detach from terminal");
        return 1;
    }

    // Execute the command with the inherited environment
    execvpe(argv[cmd_start], &argv[cmd_start], envp);
    perror("Failed to execute command");
    return 1;
}