1.\" $OpenBSD: err.3,v 1.12 2001/02/17 17:01:03 pjanzen Exp $ 2.\" 3.\" Copyright (c) 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd August 8, 1997 35.Dt ERR 3 36.Os 37.Sh NAME 38.Nm err , 39.Nm verr , 40.Nm errx , 41.Nm verrx , 42.Nm warn , 43.Nm vwarn , 44.Nm warnx , 45.Nm vwarnx 46.Nd formatted error messages 47.Sh SYNOPSIS 48.Fd #include <err.h> 49.Ft void 50.Fn err "int eval" "const char *fmt" "..." 51.Ft void 52.Fn verr "int eval" "const char *fmt" "va_list args" 53.Ft void 54.Fn errx "int eval" "const char *fmt" "..." 55.Ft void 56.Fn verrx "int eval" "const char *fmt" "va_list args" 57.Ft void 58.Fn warn "const char *fmt" "..." 59.Ft void 60.Fn vwarn "const char *fmt" "va_list args" 61.Ft void 62.Fn warnx "const char *fmt" "..." 63.Ft void 64.Fn vwarnx "const char *fmt" "va_list args" 65.Sh DESCRIPTION 66The 67.Fn err 68and 69.Fn warn 70family of functions display a formatted error message on the standard 71error output. 72In all cases, the last component of the program name, followed by 73a colon 74.Pq Sq \&: 75character and a space, are output. 76The text that follows depends on the function being called. 77The 78.Fa fmt 79specification (and associated arguments) may be any format allowed by 80.Xr printf 3 , 81a simple string, or 82.Dv NULL . 83If the 84.Fa fmt 85argument is not 86.Dv NULL , 87the formatted error message is output. 88.Pp 89In the case of the 90.Fn err , 91.Fn verr , 92.Fn warn , 93and 94.Fn vwarn 95functions only, the error message string affiliated with the current value of 96the global variable 97.Va errno 98is output (see 99.Xr strerror 3 ) , 100preceded by a colon character and a space if 101.Fa fmt 102is not 103.Dv NULL . 104That is, the output is as follows: 105.Bd -literal -offset indent 106progname: fmt: error message string 107.Ed 108.Pp 109if 110.Fa fmt 111is not 112.Dv NULL , 113or: 114.Bd -literal -offset indent 115progname: error message string 116.Ed 117.Pp 118if it is. 119.Pp 120The counterpart functions, 121.Fn errx , 122.Fn verrx , 123.Fn warnx , 124and 125.Fn vwarnx , 126do not output the error message string, so the output looks like the following: 127.Bd -literal -offset indent 128progname: fmt 129.Ed 130.Pp 131In all cases, the output is followed by a newline character. 132.Pp 133The 134.Fn err , 135.Fn verr , 136.Fn errx , 137and 138.Fn verrx 139functions do not return, but exit with the value of the argument 140.Fa eval . 141.Sh EXAMPLES 142Display the current 143.Va errno 144information string and exit: 145.Bd -literal -offset indent 146if ((p = malloc(size)) == NULL) 147 err(1, NULL); 148if ((fd = open(file_name, O_RDONLY, 0)) == -1) 149 err(1, "%s", file_name); 150.Ed 151.Pp 152Display an error message and exit: 153.Bd -literal -offset indent 154if (tm.tm_hour < START_TIME) 155 errx(1, "too early, wait until %s", start_time_string); 156.Ed 157.Pp 158Warn of an error: 159.Bd -literal -offset indent 160if ((fd = open(raw_device, O_RDONLY, 0)) == -1) 161 warnx("%s: %s: trying the block device", 162 raw_device, strerror(errno)); 163if ((fd = open(block_device, O_RDONLY, 0)) == -1) 164 err(1, "%s", block_device); 165.Ed 166.Sh SEE ALSO 167.Xr exit 3 , 168.Xr perror 3 , 169.Xr printf 3 , 170.Xr strerror 3 171.Sh HISTORY 172The 173.Fn err 174and 175.Fn warn 176functions first appeared in 177.Bx 4.4 . 178.Sh CAVEATS 179It is important never to pass a string with user-supplied data as a 180format without using 181.Ql %s . 182An attacker can put format specifiers in the string to mangle your stack, 183leading to a possible security hole. 184This holds true even if you have built the string 185.Dq by hand 186using a function like 187.Fn snprintf , 188as the resulting string may still contain user-supplied conversion specifiers 189for later interpolation by the 190.Fn err 191and 192.Fn warn 193functions. 194.Pp 195Always be sure to use the proper secure idiom: 196.Bd -literal -offset indent 197err(1, "%s", string); 198.Ed 199