.\" $NetBSD: exec.3,v 1.29.6.1 2019/09/05 08:19:42 martin Exp $ .\" .\" Copyright (c) 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)exec.3 8.3 (Berkeley) 1/24/94 .\" .Dd September 1, 2019 .Dt EXEC 3 .Os .Sh NAME .Nm execl , .Nm execlp , .Nm execlpe , .Nm execle , .Nm exect , .Nm execv , .Nm execvp , .Nm execvpe .Nd execute a file .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In unistd.h .Vt extern char **environ; .Ft int .Fn execl "const char *path" "const char *arg" ... .Ft int .Fn execlp "const char *file" "const char *arg" ... .Ft int .Fn execlpe "const char *path" "const char *arg" ... "char *const envp[]" .Ft int .Fn execle "const char *path" "const char *arg" ... "char *const envp[]" .Ft int .Fn exect "const char *path" "char *const argv[]" "char *const envp[]" .Ft int .Fn execv "const char *path" "char *const argv[]" .Ft int .Fn execvp "const char *file" "char *const argv[]" .Ft int .Fn execvpe "const char *file" "char *const argv[]" "char *const envp[]" .Sh DESCRIPTION The .Fn exec family of functions replaces the current process image with a new process image. The functions described in this manual page are front-ends for the function .Xr execve 2 . (See the manual page for .Xr execve 2 for detailed information about the replacement of the current process. The .Xr script 7 manual page provides detailed information about the execution of interpreter scripts.) .Pp The initial argument for these functions is the pathname of a file which is to be executed. .Pp The .Fa "const char *arg" and subsequent ellipses in the .Fn execl , .Fn execlp , .Fn execlpe , and .Fn execle functions can be thought of as .Em arg0 , .Em arg1 , \&..., .Em argn . Together they describe a list of one or more pointers to NUL-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 .Em must be terminated by a .Dv NULL pointer. .Pp The .Fn exect , .Fn execv , .Fn execvp , and .Fn execvpe functions provide an array of pointers to NUL-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 .Sy must be terminated by a .Dv NULL pointer. .Pp The .Fn execle , .Fn execlpe , .Fn exect , and .Fn execvpe functions also specify the environment of the executed process by following the .Dv NULL pointer that terminates the list of arguments in the parameter list or the pointer to the argv array with an additional parameter. This additional parameter is an array of pointers to NUL-terminated strings and .Em must be terminated by a .Dv NULL pointer. The other functions take the environment for the new process image from the external variable .Va environ in the current process. .Pp Some of these functions have special semantics. .Pp The functions .Fn execlp , .Fn execlpe , .Fn execvp , and .Fn execvpe will duplicate the actions of the shell in searching for an executable file if the specified file name does not contain a slash .Dq Li \&/ character. The search path is the path specified in the environment by the .Ev PATH variable. If this variable isn't specified, .Va _PATH_DEFPATH from .In paths.h is used instead, its value being: .Pa /usr/bin:/bin:/usr/pkg/bin:/usr/local/bin . In addition, certain errors are treated specially. .Pp If permission is denied for a file (the attempted .Xr execve 2 returned .Er EACCES ) , these functions will continue searching the rest of the search path. If no other file is found, however, they will return with the global variable .Va errno set to .Er EACCES . .Pp If the header of a file isn't recognized (the attempted .Xr execve 2 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.) .Pp If the file is currently busy (the attempted .Xr execve 2 returned .Er ETXTBUSY ) , these functions will sleep for several seconds, periodically re-attempting to execute the file. .Pp The function .Fn exect executes a file with the program tracing facilities enabled (see .Xr ptrace 2 ) . .Sh RETURN VALUES If any of the .Fn exec functions returns, an error will have occurred. The return value is \-1, and the global variable .Va errno will be set to indicate the error. .Sh FILES .Bl -tag -width /bin/sh -compact .It Pa /bin/sh The shell. .El .Sh COMPATIBILITY Historically, the default path for the .Fn execlp .Fn execlpe , .Fn execvp , and .Fn execvpe functions was .Dq Pa :/bin:/usr/bin . This was changed to improve security and behaviour. .Pp The behavior of .Fn execlp , .Fn execlpe , .Fn execvp , and .Fn execvpe when errors occur while attempting to execute the file is historic practice, but has not traditionally been documented and is not specified by the POSIX standard. .Pp Traditionally, the functions .Fn execlp , .Fn execlpe , .Fn execvp , and .Fn execvpe ignored all errors except for the ones described above and .Er ENOMEM and .Er E2BIG , upon which they returned. They now return if any error other than the ones described above occurs. .Sh ERRORS .Fn execl , .Fn execle , .Fn execlp , .Fn execlpe , .Fn execvp , and .Fn execvpe may fail and set .Va errno for any of the errors specified for the library functions .Xr execve 2 and .Xr malloc 3 . .Pp .Fn exect and .Fn execv may fail and set .Va errno for any of the errors specified for the library function .Xr execve 2 . .Sh SEE ALSO .Xr sh 1 , .Xr execve 2 , .Xr fork 2 , .Xr ptrace 2 , .Xr environ 7 , .Xr script 7 .Sh STANDARDS .Fn execl , .Fn execv , .Fn execle , .Fn execlp , and .Fn execvp conform to .St -p1003.1-90 . .Sh HISTORY The .Fn exec function appeared in .At v1 . The .Fn execlpe function appeared first in QNX and the .Fn execvpe function exists on both .Nx and QNX.