1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)exec.3 8.3 (Berkeley) 1/24/94 29.\" 30.Dd March 22, 2020 31.Dt EXEC 3 32.Os 33.Sh NAME 34.Nm execl , 35.Nm execlp , 36.Nm execle , 37.Nm exect , 38.Nm execv , 39.Nm execvp , 40.Nm execvP 41.Nd execute a file 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In unistd.h 46.Vt extern char **environ ; 47.Ft int 48.Fn execl "const char *path" "const char *arg" ... NULL 49.Ft int 50.Fn execlp "const char *file" "const char *arg" ... NULL 51.Ft int 52.Fn execle "const char *path" "const char *arg" ... NULL "char *const envp[]" 53.Fc 54.Ft int 55.Fn exect "const char *path" "char *const argv[]" "char *const envp[]" 56.Ft int 57.Fn execv "const char *path" "char *const argv[]" 58.Ft int 59.Fn execvp "const char *file" "char *const argv[]" 60.Ft int 61.Fn execvP "const char *file" "const char *search_path" "char *const argv[]" 62.Sh DESCRIPTION 63The 64.Nm exec 65family of functions replaces the current process image with a 66new process image. 67The functions described in this manual page are front-ends for the function 68.Xr execve 2 . 69(See the manual page for 70.Xr execve 2 71for detailed information about the replacement of the current process.) 72.Pp 73The initial argument for these functions is the pathname of a file which 74is to be executed. 75.Pp 76The 77.Fa "const char *arg" 78and subsequent ellipses in the 79.Fn execl , 80.Fn execlp , 81and 82.Fn execle 83functions can be thought of as 84.Em arg0 , 85.Em arg1 , 86\&..., 87.Em argn . 88Together they describe a list of one or more pointers to null-terminated 89strings that represent the argument list available to the executed program. 90The first argument, by convention, should point to the file name associated 91with the file being executed. 92The list of arguments 93.Em must 94be terminated by a 95.Dv NULL 96pointer. 97.Pp 98The 99.Fn exect , 100.Fn execv , 101.Fn execvp , 102and 103.Fn execvP 104functions provide an array of pointers to null-terminated strings that 105represent the argument list available to the new program. 106The first argument, by convention, should point to the file name associated 107with the file being executed. 108The array of pointers 109.Sy must 110be terminated by a 111.Dv NULL 112pointer. 113.Pp 114The 115.Fn execle 116and 117.Fn exect 118functions also specify the environment of the executed process by following 119the 120.Dv NULL 121pointer that terminates the list of arguments in the argument list 122or the pointer to the argv array with an additional argument. 123This additional argument is an array of pointers to null-terminated strings 124and 125.Em must 126be terminated by a 127.Dv NULL 128pointer. 129The other functions take the environment for the new process image from the 130external variable 131.Va environ 132in the current process. 133.Pp 134Some of these functions have special semantics. 135.Pp 136The functions 137.Fn execlp , 138.Fn execvp , 139and 140.Fn execvP 141will duplicate the actions of the shell in searching for an executable file 142if the specified file name does not contain a slash 143.Dq Li / 144character. 145For 146.Fn execlp 147and 148.Fn execvp , 149search path is the path specified in the environment by 150.Dq Ev PATH 151variable. 152If this variable is not specified, 153the default path is set according to the 154.Dv _PATH_DEFPATH 155definition in 156.In paths.h , 157which is set to 158.Dq Ev /sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin . 159For 160.Fn execvP , 161the search path is specified as an argument to the function. 162In addition, certain errors are treated specially. 163.Pp 164If an error is ambiguous (for simplicity, we shall consider all 165errors except 166.Er ENOEXEC 167as being ambiguous here, although only the critical error 168.Er EACCES 169is really ambiguous), 170then these functions will act as if they stat the file to determine 171whether the file exists and has suitable execute permissions. 172If it does, they will return immediately with the global variable 173.Va errno 174restored to the value set by 175.Fn execve . 176Otherwise, the search will be continued. 177If the search completes without performing a successful 178.Fn execve 179or terminating due to an error, 180these functions will return with the global variable 181.Va errno 182set to 183.Er EACCES 184or 185.Er ENOENT 186according to whether at least one file with suitable execute permissions 187was found. 188.Pp 189If the header of a file is not recognized (the attempted 190.Fn execve 191returned 192.Er ENOEXEC ) , 193these functions will execute the shell with the path of 194the file as its first argument. 195(If this attempt fails, no further searching is done.) 196.Pp 197The function 198.Fn exect 199executes a file with the program tracing facilities enabled (see 200.Xr ptrace 2 ) . 201.Sh RETURN VALUES 202If any of the 203.Fn exec 204functions returns, an error will have occurred. 205The return value is \-1, and the global variable 206.Va errno 207will be set to indicate the error. 208.Sh FILES 209.Bl -tag -width /bin/sh -compact 210.It Pa /bin/sh 211The shell. 212.El 213.Sh COMPATIBILITY 214Historically, the default path for the 215.Fn execlp 216and 217.Fn execvp 218functions was 219.Dq Pa :/bin:/usr/bin . 220This was changed to remove the current directory to enhance system 221security. 222.Pp 223The behavior of 224.Fn execlp 225and 226.Fn execvp 227when errors occur while attempting to execute the file is not quite historic 228practice, and has not traditionally been documented and is not specified 229by the 230.Tn POSIX 231standard. 232.Pp 233Traditionally, the functions 234.Fn execlp 235and 236.Fn execvp 237ignored all errors except for the ones described above and 238.Er ETXTBSY , 239upon which they retried after sleeping for several seconds, and 240.Er ENOMEM 241and 242.Er E2BIG , 243upon which they returned. 244They now return for 245.Er ETXTBSY , 246and determine existence and executability more carefully. 247In particular, 248.Er EACCES 249for inaccessible directories in the path prefix is no longer 250confused with 251.Er EACCES 252for files with unsuitable execute permissions. 253In 254.Bx 4.4 , 255they returned upon all errors except 256.Er EACCES , 257.Er ENOENT , 258.Er ENOEXEC 259and 260.Er ETXTBSY . 261This was inferior to the traditional error handling, 262since it breaks the ignoring of errors for path prefixes 263and only improves the handling of the unusual ambiguous error 264.Er EFAULT 265and the unusual error 266.Er EIO . 267The behaviour was changed to match the behaviour of 268.Xr sh 1 . 269.Sh ERRORS 270The 271.Fn execl , 272.Fn execle , 273.Fn execlp , 274.Fn execvp 275and 276.Fn execvP 277functions 278may fail and set 279.Va errno 280for any of the errors specified for the library functions 281.Xr execve 2 282and 283.Xr malloc 3 . 284.Pp 285The 286.Fn exect 287and 288.Fn execv 289functions 290may fail and set 291.Va errno 292for any of the errors specified for the library function 293.Xr execve 2 . 294.Sh SEE ALSO 295.Xr sh 1 , 296.Xr execve 2 , 297.Xr fork 2 , 298.Xr ktrace 2 , 299.Xr ptrace 2 , 300.Xr environ 7 301.Sh STANDARDS 302The 303.Fn execl , 304.Fn execv , 305.Fn execle , 306.Fn execlp 307and 308.Fn execvp 309functions 310conform to 311.St -p1003.1-88 . 312.Sh HISTORY 313The 314.Fn exec 315function appeared in 316.At v1 . 317The 318.Fn execl 319and 320.Fn execv 321functions appeared in 322.At v2 . 323The 324.Fn execlp , 325.Fn execle , 326.Fn execve , 327and 328.Fn execvp 329functions appeared in 330.At v7 . 331The 332.Fn execvP 333function first appeared in 334.Fx 5.2 . 335.Sh BUGS 336The type of the 337.Fa argv 338and 339.Fa envp 340parameters to 341.Fn execle , 342.Fn exect , 343.Fn execv , 344.Fn execvp , 345and 346.Fn execvP 347is a historical accident and no sane implementation should modify the provided 348strings. 349The bogus parameter types trigger false positives from 350.Li const 351correctness analyzers. 352On 353.Fx , 354the 355.Fn __DECONST 356macro may be used to work around this limitation. 357.Pp 358Due to a fluke of the C standard, on platforms other than 359.Fx 360the definition of 361.Dv NULL 362may be the untyped number zero, rather than a 363.Ad (void *)0 364expression. 365To distinguish the concepts, they are referred to as a 366.Dq null pointer constant 367and a 368.Dq null pointer , 369respectively. 370On exotic computer architectures that 371.Fx 372does not support, the null pointer constant and null pointer may have a 373different representation. 374In general, where this document and others reference a 375.Dv NULL 376value, they actually imply a null pointer. 377E.g., for portability to non-FreeBSD operating systems on exotic computer 378architectures, one may use 379.Li (char *)NULL 380in place of 381.Dv NULL 382when invoking 383.Fn execl , 384.Fn execle , 385and 386.Fn execlp . 387