POSIX_Shell/redirection.cpp at main · AyanRoy24/POSIX_Shell · GitHub

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#include "headers.h"

static string trimSpaces(const string &s)
{
    size_t a = s.find_first_not_of(" \t");
    if (a == string::npos)
        return "";
    size_t b = s.find_last_not_of(" \t");
    return s.substr(a, b - a + 1);
}

// args is the redirection-tokenized command: [ "cmd args", "<"|">"|">>", file, ... ]
void redirection(vector<string> args)
{
    int inputFd = -1;
    int outputFd = -1;
    vector<string> commandParts;

    for (size_t i = 0; i < args.size(); ++i)
    {
        const string &tok = args[i];

        if (tok == "<" || tok == ">" || tok == ">>")
        {
            if (i + 1 >= args.size())
            {
                cerr << "Syntax error: missing file name after '" << tok << "'" << endl;
                if (inputFd != -1)
                    close(inputFd);
                if (outputFd != -1)
                    close(outputFd);
                return;
            }

            string fileName = trimSpaces(args[++i]);

            if (tok == "<")
            {
                if (inputFd != -1)
                    close(inputFd);
                inputFd = open(fileName.c_str(), O_RDONLY);
                if (inputFd == -1)
                {
                    cerr << "cannot open '" << fileName << "': " << strerror(errno) << endl;
                    if (outputFd != -1)
                        close(outputFd);
                    return;
                }
            }
            else
            {
                int flags = O_WRONLY | O_CREAT | (tok == ">>" ? O_APPEND : O_TRUNC);
                if (outputFd != -1)
                    close(outputFd);
                outputFd = open(fileName.c_str(), flags, 0644);
                if (outputFd == -1)
                {
                    cerr << "cannot open '" << fileName << "': " << strerror(errno) << endl;
                    if (inputFd != -1)
                        close(inputFd);
                    return;
                }
            }
        }
        else
        {
            string part = trimSpaces(tok);
            if (!part.empty())
                commandParts.push_back(part);
        }
    }

    vector<string> cmd;
    for (const string &part : commandParts)
    {
        vector<string> t = tokenize(part);
        cmd.insert(cmd.end(), t.begin(), t.end());
    }

    if (cmd.empty())
    {
        if (inputFd != -1)
            close(inputFd);
        if (outputFd != -1)
            close(outputFd);
        cerr << "Syntax error: no command to run" << endl;
        return;
    }

    pid_t pid = fork();
    if (pid == 0)
    {
        signal(SIGINT, SIG_DFL);
        signal(SIGTSTP, SIG_DFL);

        if (inputFd != -1)
        {
            dup2(inputFd, STDIN_FILENO);
            close(inputFd);
        }
        if (outputFd != -1)
        {
            dup2(outputFd, STDOUT_FILENO);
            close(outputFd);
        }

        char **argv = new char *[cmd.size() + 1];
        for (size_t i = 0; i < cmd.size(); ++i)
        {
            argv[i] = new char[cmd[i].size() + 1];
            strcpy(argv[i], cmd[i].c_str());
        }
        argv[cmd.size()] = nullptr;

        execvp(argv[0], argv);
        cerr << cmd[0] << ": command not found" << endl;
        _exit(127);
    }
    else if (pid < 0)
    {
        perror("fork");
    }
    else
    {
        if (inputFd != -1)
            close(inputFd);
        if (outputFd != -1)
            close(outputFd);
        int status = 0;
        while (waitpid(pid, &status, 0) == -1 && errno == EINTR)
            ;
    }
}