1.\" $OpenBSD: printf.1,v 1.13 2001/02/17 17:15:27 pjanzen Exp $ 2.\" 3.\" Copyright (c) 1989, 1990 The Regents of the University of California. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the Institute of Electrical and Electronics Engineers, Inc. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the University of 20.\" California, Berkeley and its contributors. 21.\" 4. Neither the name of the University nor the names of its contributors 22.\" may be used to endorse or promote products derived from this software 23.\" without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 26.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 27.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 28.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 29.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 30.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 31.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 32.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 34.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35.\" SUCH DAMAGE. 36.\" 37.\" from: @(#)printf.1 5.11 (Berkeley) 7/24/91 38.\" 39.Dd November 5, 1993 40.Dt PRINTF 1 41.Os 42.Sh NAME 43.Nm printf 44.Nd formatted output 45.Sh SYNOPSIS 46.Nm printf 47.Ar format 48.Op Ar arguments ... 49.Sh DESCRIPTION 50.Nm printf 51formats and prints its arguments, after the first, under control 52of the 53.Ar format . 54The 55.Ar format 56is a character string which contains three types of objects: plain characters, 57which are simply copied to standard output, character escape sequences which 58are converted and copied to the standard output, and format specifications, 59each of which causes printing of the next successive 60.Ar argument . 61.Pp 62The 63.Ar arguments 64after the first are treated as strings if the corresponding format is 65.Cm b , 66.Cm c 67or 68.Cm s ; 69otherwise it is evaluated as a C constant, with the following extensions: 70.Bl -bullet -offset indent 71.It 72A leading plus or minus sign is allowed. 73.It 74If the leading character is a single or double quote, the value is the 75.Tn ASCII 76code of the next character. 77.El 78.Pp 79The format string is reused as often as necessary to satisfy the 80.Ar arguments . 81Any extra format specifications are evaluated with zero or the null 82string. 83.Pp 84Character escape sequences are in backslash notation as defined in 85.St -ansiC . 86The characters and their meanings are as follows: 87.Pp 88.Bl -tag -width Ds -offset indent -compact 89.It Cm \ee 90Write an <escape> character. 91.It Cm \ea 92Write a <bell> character. 93.It Cm \eb 94Write a <backspace> character. 95.It Cm \ef 96Write a <form-feed> character. 97.It Cm \en 98Write a <new-line> character. 99.It Cm \er 100Write a <carriage return> character. 101.It Cm \et 102Write a <tab> character. 103.It Cm \ev 104Write a <vertical tab> character. 105.It Cm \e\' 106Write a <single quote> character. 107.It Cm \e\e 108Write a backslash character. 109.It Cm \e Ns Ar num 110Write an 8-bit character whose 111.Tn ASCII 112value is the 1-, 2-, or 3-digit 113octal number 114.Ar num . 115.El 116.Pp 117Each format specification is introduced by the percent 118.Pq Sq \&% 119character. 120The remainder of the format specifiers include, 121in the following order: 122.Bl -tag -width Ds 123.It "Zero or more of the following flags:" 124.Bl -tag -width Ds 125.It Cm # 126Specifies that the value should be printed in an 127.Dq alternate form . 128For the 129.Cm c , 130.Cm d , 131and 132.Cm s 133formats, this option has no effect. 134For the 135.Cm o 136format the precision of the number is increased to force the first 137character of the output string to a zero. 138For the 139.Cm x 140.Pq Cm X 141format, a non-zero result has the string 142.Li 0x 143.Pq Li 0X 144prepended to it. 145For 146.Cm e , 147.Cm E , 148.Cm f , 149.Cm g , 150and 151.Cm G 152formats, the result will always contain a decimal point, even if no 153digits follow the point (normally, a decimal point only appears in the 154results of those formats if a digit follows the decimal point). 155For 156.Cm g 157and 158.Cm G 159formats, trailing zeros are not removed from the result as they 160would otherwise be. 161.It Cm \&\- 162Specifies the 163.Em left adjustment 164of the output in the indicated field. 165.It Cm \&+ 166Specifies that there should always be 167a sign placed before the number when using signed formats. 168.It Sq \&\ \& 169A space specifies that a blank should be left before a positive number 170for a signed format. 171A 172.Ql + 173overrides a space if both are used. 174.It Cm \&0 175A zero character specifies that zero-padding should be used 176rather than blank-padding. 177This flag is ignored if used with a precision 178specifier and any of the 179.Cm d , i , o , u , 180or 181.Cm x 182.Pq Cm X 183formats. 184A 185.Ql \&- 186overrides a 187.Ql \&0 188if both are used. 189.El 190.It "Field Width:" 191An optional digit string specifying a 192.Em field width ; 193if the output string has fewer characters than the field width it will 194be blank-padded on the left (or right, if the left-adjustment indicator 195has been given) to make up the field width (note that a leading zero 196is a flag, but an embedded zero is part of a field width). 197.It Precision: 198An optional period 199.Pq Sq \&. , 200followed by an optional digit string giving a 201.Em precision 202which specifies the number of digits to appear after the decimal point, 203for 204.Cm e 205and 206.Cm f 207formats, or the maximum number of characters to be printed 208from a string; if the digit string is missing, the precision is treated 209as zero. 210.It Format: 211A character which indicates the type of format to use (one of 212.Cm diouxXfEgGbcs ) . 213.El 214.Pp 215A field width or precision may be 216.Ql \&* 217instead of a digit string. 218In this case an 219.Ar argument 220supplies the field width or precision. 221.Pp 222The format characters and their meanings are: 223.Bl -tag -width Fl 224.It Cm diouXx 225The 226.Ar argument 227is printed as a signed decimal 228.Pq Cm d No or Cm i , 229unsigned octal, unsigned decimal, 230or unsigned hexadecimal 231.Pq Cm x No or Cm X , 232respectively. 233.It Cm f 234The 235.Ar argument 236is printed in the style 237.Sm off 238.Pf [\-]ddd Cm \&. No ddd 239.Sm on 240where the number of d's 241after the decimal point is equal to the precision specification for 242the argument. 243If the precision is missing, 6 digits are given; if the precision 244is explicitly 0, no digits and no decimal point are printed. 245.It Cm eE 246The 247.Ar argument 248is printed in the style 249.Sm off 250.Pf [\-]d Cm \&. No ddd Cm e No \\*(Pmdd 251.Sm on 252where there 253is one digit before the decimal point and the number after is equal to 254the precision specification for the argument; when the precision is 255missing, 6 digits are produced. 256An upper-case 257.Sq E 258is used for an 259.Cm E 260format. 261.It Cm gG 262The 263.Ar argument 264is printed in style 265.Cm f 266or in style 267.Cm e 268.Pq Cm E 269whichever gives full precision in minimum space. 270.It Cm b 271Characters from the string 272.Ar argument 273are printed with backslash-escape sequences expanded. 274.It Cm c 275The first character of 276.Ar argument 277is printed. 278.It Cm s 279Characters from the string 280.Ar argument 281are printed until the end is reached or until the number of characters 282indicated by the precision specification is reached; however if the 283precision is 0 or missing, all characters in the string are printed. 284.It Cm \&% 285Print a 286.Ql \&% ; 287no argument is used. 288.El 289.Pp 290In no case does a non-existent or small field width cause truncation of 291a field; padding takes place only if the specified field width exceeds 292the actual width. 293.Pp 294The 295.Nm 296utility exits 0 on success or 1 on failure. 297.Sh EXAMPLES 298Convert a hexidecimal value to decimal and print it out: 299.Pp 300.D1 Ic printf \&"%d\en\&" 0x20 301.Pp 302Print the decimal representation of the character 'a' (see 303.Xr ascii 7 ) : 304.Pp 305.D1 Ic printf \&"%d\en\&" \e'a 306.Sh SEE ALSO 307.Xr echo 1 , 308.Xr printf 3 309.Sh STANDARDS 310The 311.Nm printf 312utility conforms to 313.St -p1003.2-92 . 314.Sh HISTORY 315The 316.Nm 317command appeared in 318.Bx 4.3 Reno . 319.Sh CAVEATS 320It is important never to pass a string with user-supplied data as a 321format without using 322.Ql %s . 323An attacker can put format specifiers in the string to mangle your stack, 324leading to a possible security hole. 325.Pp 326Always be sure to use the proper secure idiom: 327.Bd -literal -offset indent 328printf "%s" "$STRING" 329.Ed 330.Sh BUGS 331Since arguments are translated from 332.Tn ASCII 333to floating-point, and 334then back again, floating-point precision may be lost. 335