1.\" $OpenBSD: printf.1,v 1.22 2009/02/08 17:15:10 jmc 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. Neither the name of the University nor the names of its contributors 18.\" may be used to endorse or promote products derived from this software 19.\" without specific prior written permission. 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31.\" SUCH DAMAGE. 32.\" 33.\" from: @(#)printf.1 5.11 (Berkeley) 7/24/91 34.\" 35.Dd $Mdocdate: February 8 2009 $ 36.Dt PRINTF 1 37.Os 38.Sh NAME 39.Nm printf 40.Nd formatted output 41.Sh SYNOPSIS 42.Nm printf 43.Ar format 44.Op Ar arguments ... 45.Sh DESCRIPTION 46.Nm printf 47formats and prints its arguments, after the first, under control 48of the 49.Ar format . 50The 51.Ar format 52is a character string which contains three types of objects: plain characters, 53which are simply copied to standard output, character escape sequences which 54are converted and copied to the standard output, and format specifications, 55each of which causes printing of the next successive 56.Ar argument . 57.Pp 58The 59.Ar arguments 60after the first are treated as strings if the corresponding format is 61.Cm b , 62.Cm c 63or 64.Cm s ; 65otherwise it is evaluated as a C constant, with the following extensions: 66.Bl -bullet -offset indent 67.It 68A leading plus or minus sign is allowed. 69.It 70If the leading character is a single or double quote, the value is the 71.Tn ASCII 72code of the next character. 73.El 74.Pp 75The format string is reused as often as necessary to satisfy the 76.Ar arguments . 77Any extra format specifications are evaluated with zero or the null 78string. 79.Pp 80Character escape sequences are in backslash notation as defined in 81.St -ansiC . 82The characters and their meanings are as follows: 83.Pp 84.Bl -tag -width Ds -offset indent -compact 85.It Cm \ee 86Write an <escape> character. 87.It Cm \ea 88Write a <bell> character. 89.It Cm \eb 90Write a <backspace> character. 91.It Cm \ef 92Write a <form-feed> character. 93.It Cm \en 94Write a <new-line> character. 95.It Cm \er 96Write a <carriage return> character. 97.It Cm \et 98Write a <tab> character. 99.It Cm \ev 100Write a <vertical tab> character. 101.It Cm \e\' 102Write a <single quote> character. 103.It Cm \e\e 104Write a backslash character. 105.It Cm \e Ns Ar num 106Write an 8-bit character whose 107.Tn ASCII 108value is the 1-, 2-, or 3-digit 109octal number 110.Ar num . 111.El 112.Pp 113Each format specification is introduced by the percent 114.Pq Sq \&% 115character. 116The remainder of the format specifiers include, 117in the following order: 118.Bl -tag -width Ds 119.It "Zero or more of the following flags:" 120.Bl -tag -width Ds 121.It Cm # 122Specifies that the value should be printed in an 123.Dq alternate form . 124For the 125.Cm c , 126.Cm d , 127and 128.Cm s 129formats, this option has no effect. 130For the 131.Cm o 132format the precision of the number is increased to force the first 133character of the output string to a zero. 134For the 135.Cm x 136.Pq Cm X 137format, a non-zero result has the string 138.Li 0x 139.Pq Li 0X 140prepended to it. 141For 142.Cm a , 143.Cm A , 144.Cm e , 145.Cm E , 146.Cm f , 147.Cm F , 148.Cm g , 149and 150.Cm G 151formats, the result will always contain a decimal point, even if no 152digits follow the point (normally, a decimal point only appears in the 153results of those formats if a digit follows the decimal point). 154For 155.Cm g 156and 157.Cm G 158formats, trailing zeros are not removed from the result as they 159would otherwise be. 160.It Cm \&\- 161Specifies the 162.Em left adjustment 163of the output in the indicated field. 164.It Cm \&+ 165Specifies that there should always be 166a sign placed before the number when using signed formats. 167.It Sq \&\ \& 168A space specifies that a blank should be left before a positive number 169for a signed format. 170A 171.Ql + 172overrides a space if both are used. 173.It Cm \&0 174A zero character specifies that zero-padding should be used 175rather than blank-padding. 176This flag is ignored if used with a precision 177specifier and any of the 178.Cm d , i , o , u , 179or 180.Cm x 181.Pq Cm X 182formats. 183A 184.Ql \&- 185overrides a 186.Ql \&0 187if both are used. 188.El 189.It "Field Width:" 190An optional digit string specifying a 191.Em field width ; 192if the output string has fewer characters than the field width it will 193be blank-padded on the left (or right, if the left-adjustment indicator 194has been given) to make up the field width (note that a leading zero 195is a flag, but an embedded zero is part of a field width). 196.It Precision: 197An optional period 198.Pq Sq \&. , 199followed by an optional digit string giving a 200.Em precision 201which specifies the number of digits to appear after the decimal point, 202for 203.Cm e 204and 205.Cm f 206formats, or the maximum number of characters to be printed 207from a string; if the digit string is missing, the precision is treated 208as zero. 209.It Format: 210A character which indicates the type of format to use (one of 211.Cm diouxXfFeEgGaAbcs ) . 212.El 213.Pp 214A field width or precision may be 215.Ql \&* 216instead of a digit string. 217In this case an 218.Ar argument 219supplies the field width or precision. 220.Pp 221The format characters and their meanings are: 222.Bl -tag -width Fl 223.It Cm diouXx 224The 225.Ar argument 226is printed as a signed decimal 227.Pq Cm d No or Cm i , 228unsigned octal, unsigned decimal, 229or unsigned hexadecimal 230.Pq Cm x No or Cm X , 231respectively. 232.It Cm fF 233The 234.Ar argument 235is printed in the style 236.Sm off 237.Pf [\-]ddd Cm \&. No ddd 238.Sm on 239where the number of d's 240after the decimal point is equal to the precision specification for 241the argument. 242If the precision is missing, 6 digits are given; if the precision 243is explicitly 0, no digits and no decimal point are printed. 244.Pp 245If the argument is infinity, it will be converted to [-]inf 246.Pq Cm f 247or [-]INF 248.Pq Cm F , 249respectively. 250If the argument is not-a-number (NaN), it will be converted to 251[-]nan 252.Pq Cm f 253or [-]NAN 254.Pq Cm F , 255respectively. 256.It Cm eE 257The 258.Ar argument 259is printed in the style 260.Sm off 261.Pf [\-]d Cm \&. No ddd Cm e No \\*(Pmdd 262.Sm on 263where there 264is one digit before the decimal point and the number after is equal to 265the precision specification for the argument; when the precision is 266missing, 6 digits are produced. 267An upper-case 268.Sq E 269is used for an 270.Cm E 271format. 272.Pp 273If the argument is infinity, it will be converted to [-]inf 274.Pq Cm e 275or [-]INF 276.Pq Cm E , 277respectively. 278If the argument is not-a-number (NaN), it will be converted to 279[-]nan 280.Pq Cm e 281or [-]NAN 282.Pq Cm E , 283respectively. 284.It Cm gG 285The 286.Ar argument 287is printed in style 288.Cm f 289or in style 290.Cm e 291.Pq Cm E 292whichever gives full precision in minimum space. 293.Pp 294If the argument is infinity, it will be converted to [-]inf 295.Pq Cm g 296or [-]INF 297.Pq Cm G , 298respectively. 299If the argument is not-a-number (NaN), it will be converted to 300[-]nan 301.Pq Cm g 302or [-]NAN 303.Pq Cm G , 304respectively. 305.It Cm aA 306The 307.Ar argument 308is printed in style 309.Sm off 310.Pf [\-]0xh Cm \&. No hhh Cm p No [\\*(Pm]d 311.Sm on 312where there is one digit before the hexadecimal point and the number 313after is equal to the precision specification for the argument. 314When the precision is missing, enough digits are produced to convey 315the argument's exact double-precision floating-point representation. 316.Pp 317If the argument is infinity, it will be converted to [-]inf 318.Pq Cm a 319or [-]INF 320.Pq Cm A , 321respectively. 322If the argument is not-a-number (NaN), it will be converted to 323[-]nan 324.Pq Cm a 325or [-]NAN 326.Pq Cm A , 327respectively. 328.It Cm b 329Characters from the string 330.Ar argument 331are printed with backslash-escape sequences expanded. 332.It Cm c 333The first character of 334.Ar argument 335is printed. 336.It Cm s 337Characters from the string 338.Ar argument 339are printed until the end is reached or until the number of characters 340indicated by the precision specification is reached; however if the 341precision is 0 or missing, all characters in the string are printed. 342.It Cm \&% 343Print a 344.Ql \&% ; 345no argument is used. 346.El 347.Pp 348In no case does a non-existent or small field width cause truncation of 349a field; padding takes place only if the specified field width exceeds 350the actual width. 351.Pp 352The 353.Nm 354utility exits 0 on success or 1 on failure. 355.Sh EXAMPLES 356Convert a hexadecimal value to decimal and print it out: 357.Pp 358.D1 Ic $ printf \&"%d\en\&" 0x20 359.Pp 360Print the decimal representation of the character 'a' (see 361.Xr ascii 7 ) : 362.Pp 363.D1 Ic $ printf \&"%d\en\&" \e'a 364.Sh SEE ALSO 365.Xr echo 1 , 366.Xr printf 3 367.Sh STANDARDS 368The 369.Nm 370utility is compliant with the 371.St -p1003.1-2008 372specification. 373.Sh HISTORY 374The 375.Nm 376command appeared in 377.Bx 4.3 Reno . 378.Sh CAVEATS 379It is important never to pass a string with user-supplied data as a 380format without using 381.Ql %s . 382An attacker can put format specifiers in the string to mangle your stack, 383leading to a possible security hole. 384.Pp 385Always be sure to use the proper secure idiom: 386.Bd -literal -offset indent 387printf "%s" "$STRING" 388.Ed 389.Sh BUGS 390Since arguments are translated from 391.Tn ASCII 392to floating-point, and 393then back again, floating-point precision may be lost. 394