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Questions and Answers
What is the purpose of the execl function in C?
What is the purpose of the execl function in C?
To execute an executable program with a specified path and list of command line arguments.
How does the execv function differ from execl?
How does the execv function differ from execl?
The execv function takes a path name and a pointer to a list of character pointers (like argv[]) as command line arguments.
What does the fork() function do in C?
What does the fork() function do in C?
The fork() function creates a new process by duplicating the existing process.
How many distinct outputs are possible from the code segment: int main() { fork(); printf("a"); fork(); printf("b"); return 0; }?
How many distinct outputs are possible from the code segment: int main() { fork(); printf("a"); fork(); printf("b"); return 0; }?
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What is the purpose of the args array in the execv function call?
What is the purpose of the args array in the execv function call?
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What is the purpose of the execv function?
What is the purpose of the execv function?
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How is the list of arguments terminated in the execl function?
How is the list of arguments terminated in the execl function?
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In the code segment int main() { fork(); printf("a"); fork(); printf("b"); return 0; }, how many distinct outputs are possible?
In the code segment int main() { fork(); printf("a"); fork(); printf("b"); return 0; }, how many distinct outputs are possible?
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What does the fork() function do in C?
What does the fork() function do in C?
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What is the purpose of the args array in the execv function call?
What is the purpose of the args array in the execv function call?
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How is the second argument passed to the execv function?
How is the second argument passed to the execv function?
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What is the purpose of the argv parameter in the execv function?
What is the purpose of the argv parameter in the execv function?
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How is the execv function different from the execl function?
How is the execv function different from the execl function?
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What happens after the fork() function is called in a C program?
What happens after the fork() function is called in a C program?
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How does the execv function handle the execution of a new program?
How does the execv function handle the execution of a new program?
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Study Notes
Exec System Call
- The exec system call is used when a new process is not part of the same program as the parent process, such as when a user starts a command in a shell.
- Exec replaces the contents of the currently running process with the information from a program binary.
Characteristics of Exec
- The exec function is a family of six functions, each with slightly different calling conventions and use.
- Exec is declared in the same location as fork.
- Exec completely replaces the calling process's image with that of the program being executed.
- Unlike fork, exec does not generate a new PID, as it replaces the original process.
- If successful, the exec calls do not return, as the calling image is lost.
Prototypes of Exec
- There are six prototypes of exec:
- execl
- execlp
- execv
- execvp
- execle
- execve
Naming Convention of Exec
- The naming convention for the "exec" system calls reflects their functionality:
- The function starts with "exec", indicating that it is part of the exec family.
- The next letter indicates if the call takes its arguments in a "list format" or as a pointer to an "array of arguments".
- The presence of a "p" indicates that the current PATH string should be used when searching for executable files.
- Functions whose name ends with an "e" allow passing an array to set a new environment.
Execl
- The execl function requires each command-line argument to the new program to be specified as separate arguments, terminated by a NULL pointer.
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Description
Explore the concept of exec system call in operating systems, which allows a new process to run independently from the parent process. Learn how exec replaces the current process image and loads a new program for execution.
