Use and comparison of execl functions in Linux

	Execl (Execution file)
Related functions	Fork, execle, execlp, execv, execve, execvp
Header file	# Include <unistd. h>
Define functions	Int execl (const char * path, const char * Arg ,....);
Function Description	Execl () is used to execute the file path represented by the path string parameter. The following parameter indicates that the previous argv (0), argv [1]…, The last parameter must end with a null pointer.
Return Value	If the execution is successful, the function will not return. If the execution fails,-1 will be returned. The cause of the failure is stored in errno.
Example	# Include <unistd. h> Main () { Execl ("/bin/ls", "ls", "-Al", "/etc/passwd", (char *) 0 ); }
Run	/* Run/bin/LS-Al/etc/passwd */ -RW-r -- 1 Root 705 Sep 3 13: 52/etc/passwd
	Execlp (find and execute files from PATH environment variables)
Related functions	Fork, execl, execle, execv, execve, execvp
Header file	# Include <unistd. h>
Define functions	Int execlp (const char * file, const char * Arg ,......);
Function Description	Execlp () searches for the file name that matches the parameter file from the directory indicated by the PATH environment variable, and then runs the file, then, the second parameter is used as the argv [0], argv [1]…, The last parameter must end with a null pointer.
Return Value	If the execution is successful, the function will not return. If the execution fails,-1 will be returned. The cause of the failure is stored in errno.
Error Code	See execve ().
Example	/* Execute LS-Al/etc/passwd execlp () and find/bin/ls */According to/bin in the PATH variable */ # Include <unistd. h> Main () { Execlp ("ls", "ls", "-Al", "/etc/passwd", (char *) 0 ); }
Run	-RW-r -- 1 Root 705 Sep 3 13: 52/etc/passwd
	Execv (Execution file)
Related functions	Fork, execl, execle, execlp, execve, execvp
Header file	# Include <unistd. h>
Define functions	Int execv (const char * path, char * const argv []);
Function Description	Execv () is used to execute the file path represented by the path string parameter. Unlike execl (), execve () requires only two parameters, the second parameter uses an array pointer to pass to the execution file.
Return Value	If the execution is successful, the function will not return. If the execution fails,-1 will be returned. The cause of the failure is stored in errno.
Error Code	See execve ().
Example	/* Run/bin/LS-Al/etc/passwd */ # Include <unistd. h> Main () { Char * argv [] = {"ls", "-Al", "/etc/passwd", (char *)}}; Execv ("/bin/ls", argv ); }
Run	-RW-r -- 1 Root 705 Sep 3 13: 52/etc/passwd
	Execve (Execution file)
Related functions	Fork, execl, execle, execlp, execv, execvp
Header file	# Include <unistd. h>
Define functions	Int execve (const char * filename, char * const argv [], char * const envp []);
Function Description	Execve () is used to execute the file path represented by the filename string parameter. The second parameter is passed to the execution file using the array pointer, the last parameter is an array of new environment variables passed to the execution file.
Return Value	If the execution is successful, the function will not return. If the execution fails,-1 will be returned. The cause of the failure is stored in errno.
Error Code	Eacces 1. the file to be executed does not have the executable permissions of the user. 2. The file system of the file to be executed is mounted in noexec mode. 3. The file or script translator to be executed is not a general file. Eperm 1. The process is in tracing mode, and the executor does not have the root permission. The file to be executed has the suid or sgid bit. 2. The file system of the file to be executed is mounted in nosuid mode. The file to be executed has suid or sgid, but the performer does not have root permission. The e2big parameter array is too large. Enoexec cannot determine the format of the execution file to be executed. It may be a format error or cannot be executed on this platform. The string address specified by the efault parameter filename is out of the accessible space range. The length of the string specified by the enametoolong parameter filename is too long. The file specified by the enoent parameter filename string does not exist. Insufficient enomem core memory The directory path contained in the filename string of the enotdir parameter is not a valid directory. The directory path contained in the filename string of the eacces parameter cannot be accessed and the permission is insufficient. Too many symbolic connections in eloop The file to be executed by etxtbusy has been opened by other processes and is writing data to the file. Eio I/O Access Error Enfile has reached the total number of open files allowed by the system. Emfile has reached the total number of files that the system allows a single process to open. Einval: the elf execution format of the file to be executed is not only one pt_interp section. The eisdir elf translator is a directory. The elibbad elf translator has a problem.
Example	# Include <unistd. h> Main () { Char * argv [] = {"ls", "-Al", "/etc/passwd", (char *) 0 }; Char * envp [] = {"Path =/bin", 0} Execve ("/bin/ls", argv, envp ); }
Run	-RW-r -- 1 Root 705 Sep 3 13: 52/etc/passwd
	Execvp (Execution file)
Related functions	Fork, execl, execle, execlp, execv, execve
Header file	# Include <unistd. h>
Define functions	Int execvp (const char * file, char * const argv []);
Function Description	Execvp () searches for the file name that matches the parameter file from the directory indicated by the PATH environment variable, finds the file, executes the file, and passes the second parameter argv to the file to be executed.
Return Value	If the execution is successful, the function will not return. If the execution fails,-1 will be returned. The cause of the failure is stored in errno.
Error Code	See execve ().
Example	/* Compare with the execlp () Example */ # Include <unistd. h> Main () { Char * argv [] = {"ls", "-Al", "/etc/passwd", 0 }; Execvp ("ls", argv ); }
Run	-RW-r -- 1 Root 705 Sep 3 13: 52/etc/passwd