Copyright (c) 2001 Andrew R. Reiter
Copyright (c) 2004 Joerg Wunsch
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.Dd May 9, 2020 .Dt PRINTF 9 .Os .Sh NAME .Nm printf , .Nm uprintf , .Nm tprintf , .Nm log .Nd formatted output conversion .Sh SYNOPSIS n sys/types.h n sys/systm.h .Ft int .Fn printf "const char *fmt" ... .Ft void .Fn tprintf "struct proc *p" "int pri" "const char *fmt" ... .Ft int .Fn uprintf "const char *fmt" ... .Ft int .Fn vprintf "const char *fmt" "va_list ap" n sys/syslog.h .Ft void .Fn log "int pri" "const char *fmt" ... .Ft void .Fn vlog "int pri" "const char *fmt" "va_list ap" .Sh DESCRIPTION The .Xr printf 9 family of functions are similar to the .Xr printf 3 family of functions. The different functions each use a different output stream. The .Fn uprintf function outputs to the current process' controlling tty, while .Fn printf writes to the console as well as to the logging facility. The .Fn tprintf function outputs to the tty associated with the process .Fa p and the logging facility if .Fa pri is not -1. The .Fn log function sends the message to the kernel logging facility, using the log level as indicated by .Fa pri , and to the console if no process is yet reading the log.
p Each of these related functions use the .Fa fmt parameter in the same manner as .Xr printf 3 . However, .Xr printf 9 adds two other conversion specifiers and omits one.
p The .Cm %b identifier expects two arguments: an .Vt int and a .Vt "char *" . These are used as a register value and a print mask for decoding bitmasks. The print mask is made up of two parts: the base and the arguments. The base value is the output base expressed as an integer value; for example, \e10 gives octal and \e20 gives hexadecimal. The arguments are made up of a sequence of bit identifiers. Each bit identifier begins with an integer value which is the number of the bit (starting from 1) this identifier describes. The rest of the identifier is a string of characters containing the name of the bit. The string is terminated by either the bit number at the start of the next bit identifier or .Dv NUL for the last bit identifier.
p The .Cm %D identifier is meant to assist in hexdumps. It requires two arguments: a .Vt "u_char *" pointer and a .Vt "char *" string. The memory pointed to by the pointer is output in hexadecimal one byte at a time. The string is used as a delimiter between individual bytes. If present, a width directive will specify the number of bytes to display. By default, 16 bytes of data are output.
p The .Cm %n conversion specifier is not supported.
p The .Fn log function uses .Xr syslog 3 level values .Dv LOG_DEBUG through .Dv LOG_EMERG for its .Fa pri parameter (mistakenly called .Sq priority here). Alternatively, if a .Fa pri of -1 is given, the message will be appended to the last log message started by a previous call to .Fn log . As these messages are generated by the kernel itself, the facility will always be .Dv LOG_KERN . .Sh RETURN VALUES The .Fn printf and the .Fn uprintf functions return the number of characters displayed. .Sh EXAMPLES This example demonstrates the use of the .Cm %b and .Cm %D conversion specifiers. The function d -literal -offset indent void printf_test(void) { printf("reg=%b\en", 3, "\e10\e2BITTWO\e1BITONE"); printf("out: %4D\en", "AAAA", ":"); } .Ed
p will produce the following output: d -literal -offset indent reg=3<BITTWO,BITONE> out: 41:41:41:41 .Ed
p The call d -literal -offset indent log(LOG_DEBUG, "%s%d: been there.\en", sc->sc_name, sc->sc_unit); .Ed
p will add the appropriate debug message at priority .Dq Li kern.debug to the system log. .Sh SEE ALSO .Xr printf 3 , .Xr syslog 3