1.\" $OpenBSD: printf.1,v 1.18 2007/05/31 19:20:14 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: May 31 2007 $ 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 e , 143.Cm E , 144.Cm f , 145.Cm g , 146and 147.Cm G 148formats, the result will always contain a decimal point, even if no 149digits follow the point (normally, a decimal point only appears in the 150results of those formats if a digit follows the decimal point). 151For 152.Cm g 153and 154.Cm G 155formats, trailing zeros are not removed from the result as they 156would otherwise be. 157.It Cm \&\- 158Specifies the 159.Em left adjustment 160of the output in the indicated field. 161.It Cm \&+ 162Specifies that there should always be 163a sign placed before the number when using signed formats. 164.It Sq \&\ \& 165A space specifies that a blank should be left before a positive number 166for a signed format. 167A 168.Ql + 169overrides a space if both are used. 170.It Cm \&0 171A zero character specifies that zero-padding should be used 172rather than blank-padding. 173This flag is ignored if used with a precision 174specifier and any of the 175.Cm d , i , o , u , 176or 177.Cm x 178.Pq Cm X 179formats. 180A 181.Ql \&- 182overrides a 183.Ql \&0 184if both are used. 185.El 186.It "Field Width:" 187An optional digit string specifying a 188.Em field width ; 189if the output string has fewer characters than the field width it will 190be blank-padded on the left (or right, if the left-adjustment indicator 191has been given) to make up the field width (note that a leading zero 192is a flag, but an embedded zero is part of a field width). 193.It Precision: 194An optional period 195.Pq Sq \&. , 196followed by an optional digit string giving a 197.Em precision 198which specifies the number of digits to appear after the decimal point, 199for 200.Cm e 201and 202.Cm f 203formats, or the maximum number of characters to be printed 204from a string; if the digit string is missing, the precision is treated 205as zero. 206.It Format: 207A character which indicates the type of format to use (one of 208.Cm diouxXfEgGbcs ) . 209.El 210.Pp 211A field width or precision may be 212.Ql \&* 213instead of a digit string. 214In this case an 215.Ar argument 216supplies the field width or precision. 217.Pp 218The format characters and their meanings are: 219.Bl -tag -width Fl 220.It Cm diouXx 221The 222.Ar argument 223is printed as a signed decimal 224.Pq Cm d No or Cm i , 225unsigned octal, unsigned decimal, 226or unsigned hexadecimal 227.Pq Cm x No or Cm X , 228respectively. 229.It Cm f 230The 231.Ar argument 232is printed in the style 233.Sm off 234.Pf [\-]ddd Cm \&. No ddd 235.Sm on 236where the number of d's 237after the decimal point is equal to the precision specification for 238the argument. 239If the precision is missing, 6 digits are given; if the precision 240is explicitly 0, no digits and no decimal point are printed. 241.It Cm eE 242The 243.Ar argument 244is printed in the style 245.Sm off 246.Pf [\-]d Cm \&. No ddd Cm e No \\*(Pmdd 247.Sm on 248where there 249is one digit before the decimal point and the number after is equal to 250the precision specification for the argument; when the precision is 251missing, 6 digits are produced. 252An upper-case 253.Sq E 254is used for an 255.Cm E 256format. 257.It Cm gG 258The 259.Ar argument 260is printed in style 261.Cm f 262or in style 263.Cm e 264.Pq Cm E 265whichever gives full precision in minimum space. 266.It Cm b 267Characters from the string 268.Ar argument 269are printed with backslash-escape sequences expanded. 270.It Cm c 271The first character of 272.Ar argument 273is printed. 274.It Cm s 275Characters from the string 276.Ar argument 277are printed until the end is reached or until the number of characters 278indicated by the precision specification is reached; however if the 279precision is 0 or missing, all characters in the string are printed. 280.It Cm \&% 281Print a 282.Ql \&% ; 283no argument is used. 284.El 285.Pp 286In no case does a non-existent or small field width cause truncation of 287a field; padding takes place only if the specified field width exceeds 288the actual width. 289.Pp 290The 291.Nm 292utility exits 0 on success or 1 on failure. 293.Sh EXAMPLES 294Convert a hexadecimal value to decimal and print it out: 295.Pp 296.D1 Ic $ printf \&"%d\en\&" 0x20 297.Pp 298Print the decimal representation of the character 'a' (see 299.Xr ascii 7 ) : 300.Pp 301.D1 Ic $ printf \&"%d\en\&" \e'a 302.Sh SEE ALSO 303.Xr echo 1 , 304.Xr printf 3 305.Sh STANDARDS 306The 307.Nm 308utility is compliant with the 309.St -p1003.1-2004 310specification. 311.Sh HISTORY 312The 313.Nm 314command appeared in 315.Bx 4.3 Reno . 316.Sh CAVEATS 317It is important never to pass a string with user-supplied data as a 318format without using 319.Ql %s . 320An attacker can put format specifiers in the string to mangle your stack, 321leading to a possible security hole. 322.Pp 323Always be sure to use the proper secure idiom: 324.Bd -literal -offset indent 325printf "%s" "$STRING" 326.Ed 327.Sh BUGS 328Since arguments are translated from 329.Tn ASCII 330to floating-point, and 331then back again, floating-point precision may be lost. 332