Execvp() function in C

The execvp() function in C is a crucial system call that facilitates the replacement of the current process with a new one specified by a given command.

It streamlines the execution of external programs or commands and handles the search for executable files effortlessly.

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Distinctive Attributes:

Executes the specified command by searching for its executable file in the directories listed in the PATH environment variable.

Embraces variable arguments, conveyed as an array, enabling adaptable argument passing.

Upon successful execution, the current process is seamlessly substituted by the new one, omitting further execution of subsequent code.

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Application and Utility:

Primary usage involves executing external programs or commands within a C program, especially beneficial in shell implementations.

Offers simplicity and convenience in executing diverse commands, effectively handling argument passing and executable path resolution.

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Pros and Advantages:

Simplifies program execution, automating the search for executable files and facilitating argument transmission.

Provides flexibility in conveying variable arguments, enhancing customization and adaptability.

Automatic resolution of executable path alleviates the need for explicit path specification, augmenting flexibility.

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Cons and Limitations:

Absence of subsequent code execution post-successful invocation necessitates careful consideration of cleanup and error handling routines.

Limited control and visibility over the new process once executed, unless employing interprocess communication mechanisms.

While error reporting via the errno variable is available, detailed error messages are not provided, mandating additional error handling procedures.

The execvp() function is an indispensable tool in C programming for executing external commands or programs seamlessly.

Its simplicity, flexible argument passing, and automated path resolution render it a preferred choice for process execution tasks.

However, considerations regarding subsequent code execution, process control, and error handling are imperative for effective utilization.

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Example:

// Program for execvp() function in C
#include<stdio.h> 
#include<unistd.h> 
#include<sys/wait.h> 

int main() {
    // Create an array of character pointers for command and arguments
    char *const argv[] = {"ls", "-l", NULL};

    // Create a child process
    pid_t pid = fork();

    // Check if fork was successful
    if (pid == -1) {
        perror("fork");
        return 1; // Exit with error code 1
    }

    // Child process
    if (pid == 0) {
        // Execute the ls command using execvp
        execvp("ls", argv);

        // If execvp fails, perror will be executed
        perror("execvp");
        return 1; // Exit with error code 1
    }

    // Parent process
    // Wait for the child process to complete
    wait(NULL);

    printf("Parent process finished.\n");

    return 0; // Exit successfully
}

Output:

total 16
-rwxr-xr-x 1 root root 14464 May  4 08:45 prog
Parent process finished.

This program creates a child process using the fork() system call. In the child process, it uses the execvp() function to execute the "ls" command with the "-l" argument.

If execvp() fails, perror() prints an error message. In the parent process, it waits for the child process to complete using the wait() function.

Finally, it prints a message indicating the completion of the parent process.