execl execlp execle exect execv execvp execvP - execute a file
The initial argument for these functions is the pathname of a file which is to be executed.
Fa const char *arg
and subsequent ellipses in the
and execle ();
functions can be thought of as arg0 arg1 ..., argn Together they describe a list of one or more pointers to null-terminated strings that represent the argument list available to the executed program. The first argument, by convention, should point to the file name associated with the file being executed. The list of arguments must be terminated by a NULL pointer.
and execvP ();
functions provide an array of pointers to null-terminated strings that represent the argument list available to the new program. The first argument, by convention, should point to the file name associated with the file being executed. The array of pointers must be terminated by a NULL pointer.
and exect ();
functions also specify the environment of the executed process by following the NULL pointer that terminates the list of arguments in the argument list or the pointer to the argv array with an additional argument. This additional argument is an array of pointers to null-terminated strings and must be terminated by a NULL pointer. The other functions take the environment for the new process image from the external variable environ in the current process.
Some of these functions have special semantics.
and execvP ();
will duplicate the actions of the shell in searching for an executable file if the specified file name does not contain a slash ``/ '' character. For execlp ();
and execvp (,);
search path is the path specified in the environment by ``PATH '' variable. If this variable is not specified, the default path is set according to the _PATH_DEFPATH definition in In paths.h , which is set to ``/usr/bin:/bin '' For execvP (,);
the search path is specified as an argument to the function. In addition, certain errors are treated specially.
If an error is ambiguous (for simplicity, we shall consider all
as being ambiguous here, although only the critical error
is really ambiguous),
then these functions will act as if they stat the file to determine
whether the file exists and has suitable execute permissions.
If it does, they will return immediately with the global variable
restored to the value set by
Otherwise, the search will be continued. If the search completes without performing a successful execve ();
or terminating due to an error, these functions will return with the global variable errno set to Er EACCES or Er ENOENT according to whether at least one file with suitable execute permissions was found.
If the header of a file is not recognized (the attempted
returned Er ENOEXEC ) , these functions will execute the shell with the path of the file as its first argument. (If this attempt fails, no further searching is done.)
executes a file with the program tracing facilities enabled (see ptrace(2)).
The behavior of
and execvp ();
when errors occur while attempting to execute the file is not quite historic practice, and has not traditionally been documented and is not specified by the POSIX standard.
Traditionally, the functions
and execvp ();
ignored all errors except for the ones described above and Er ETXTBSY , upon which they retried after sleeping for several seconds, and Er ENOMEM and Er E2BIG , upon which they returned. They now return for Er ETXTBSY , and determine existence and executability more carefully. In particular, Er EACCES for inaccessible directories in the path prefix is no longer confused with Er EACCES for files with unsuitable execute permissions. In BSD 4.4 they returned upon all errors except Er EACCES , Er ENOENT , Er ENOEXEC and Er ETXTBSY . This was inferior to the traditional error handling, since it breaks the ignoring of errors for path prefixes and only improves the handling of the unusual ambiguous error Er EFAULT and the unusual error Er EIO . The behaviour was changed to match the behaviour of sh(1).
and execv ();
functions may fail and set errno for any of the errors specified for the library function execve(2).
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Created 1996-2023 by Maxim Chirkov
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