Replacing a Process Image
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- The exec function replaces current process with a new process.
- The path of new process is specified as argument to exec.
- It is defined in header :
#include<unistd.h>
- Last argument of function should be NULL.
- It has 6 types of functions, whose prototype are :-
(i) Complete path is specified
int execl(const char * path, const char * arg0,const char * arg1,…,NULL);
(ii) If file is at one of default paths
int execlp(const char * file, const char * arg0,const char * arg1,…,NULL);
(iii) If arguments are given as an vector(array)
int execv(const char *path,char *const argv[]);
(iv) If arguments are given as an vector(array) and file is at one of default paths
int execvp(const char* file, char *const argv[]);
(v) int execle(const char *path, const char * arg0, const char * arg1,…,NULL, char *const envp[]);
(vi) int execve(const char *path, char *const argv[],char *const envp[] );
- The suffix p means to search PATH environmental variable.
- If the exec is executed successfully the statements after it will not be executed.
- It is because the current process is replaced.
- The arguments given to exec are used by main() function of new process as command line argument.
- If exec fails, it returns -1
- The open file descriptors remain open after the exec command.
- These file descriptors can be passed to exec as command and can be used by the replaced process to read/write from opened file.
- The argument is passed to exec as character.
- For this sprintf() is used.
- And for getting the file descriptors back , atoi() or integer typecasting can be used on the arguments of main().
