1.\" $OpenBSD: printf.1,v 1.34 2020/01/16 16:46:47 schwarze 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: January 16 2020 $ 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 argument ... 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 arguments after the first are treated as strings 59if the corresponding format is 60.Cm b , 61.Cm c 62or 63.Cm s ; 64otherwise it is evaluated as a C constant, with the following extensions: 65.Bl -bullet -offset indent 66.It 67A leading plus or minus sign is allowed. 68.It 69If the leading character is a single or double quote, 70the value is the ASCII code of the next character. 71.El 72.Pp 73The format string is reused as often as necessary to satisfy the arguments. 74Any extra format specifications are evaluated with zero or the null 75string. 76.Pp 77Character escape sequences are in backslash notation as defined in 78.St -ansiC . 79The characters and their meanings are as follows: 80.Pp 81.Bl -tag -width Ds -offset indent -compact 82.It Cm \ea 83Write a <bell> character. 84.It Cm \eb 85Write a <backspace> character. 86.It Cm \ee 87Write an <escape> character. 88.It Cm \ef 89Write a <form-feed> character. 90.It Cm \en 91Write a <new-line> character. 92.It Cm \er 93Write a <carriage return> character. 94.It Cm \et 95Write a <tab> character. 96.It Cm \ev 97Write a <vertical tab> character. 98.It Cm \e\(aq 99Write a <single quote> character. 100.It Cm \e\e 101Write a backslash character. 102.It Cm \e Ns Ar num 103Write an 8-bit character whose ASCII value is 104the 1-, 2-, or 3-digit octal number 105.Ar num . 106.El 107.Pp 108Each format specification is introduced by the percent 109.Pq Sq \&% 110character. 111The remainder of the format specifiers include, 112in the following order: 113.Bl -tag -width Ds 114.It "Zero or more of the following flags:" 115.Bl -tag -width Ds 116.It Cm # 117Specifies that the value should be printed in an 118.Dq alternate form . 119For the 120.Cm o 121format the precision of the number is increased to force the first 122character of the output string to a zero. 123For the 124.Cm x 125.Pq Cm X 126format, a non-zero result has the string 127.Li 0x 128.Pq Li 0X 129prepended to it. 130For 131.Cm a , 132.Cm A , 133.Cm e , 134.Cm E , 135.Cm f , 136.Cm F , 137.Cm g , 138and 139.Cm G 140formats, the result will always contain a decimal point, even if no 141digits follow the point (normally, a decimal point only appears in the 142results of those formats if a digit follows the decimal point). 143For 144.Cm g 145and 146.Cm G 147formats, trailing zeros are not removed from the result as they 148would otherwise be. 149For all other formats, behaviour is undefined. 150.It Cm \&\- 151Specifies the 152.Em left adjustment 153of the output in the indicated field. 154.It Cm \&+ 155Specifies that there should always be 156a sign placed before the number when using signed formats. 157.It Sq \&\ \& 158A space specifies that a blank should be left before a positive number 159for a signed format. 160A 161.Ql + 162overrides a space if both are used. 163.It Cm \&0 164A zero character specifies that zero-padding should be used 165rather than blank-padding. 166This flag is ignored if used with a precision 167specifier and any of the 168.Cm d , i , o , u , 169or 170.Cm x 171.Pq Cm X 172formats. 173A 174.Ql \&- 175overrides a 176.Ql \&0 177if both are used. 178.El 179.It "Field Width:" 180An optional digit string specifying a 181.Em field width ; 182if the output string has fewer characters than the field width it will 183be blank-padded on the left (or right, if the left-adjustment indicator 184has been given) to make up the field width (note that a leading zero 185is a flag, but an embedded zero is part of a field width). 186.It Precision: 187An optional period 188.Pq Sq \&. , 189followed by an optional digit string giving a 190.Em precision 191which specifies the number of digits to appear after the decimal point, 192for 193.Cm e 194and 195.Cm f 196formats, or the maximum number of bytes to be printed 197from a string; if the digit string is missing, the precision is treated 198as zero. 199.It Format: 200A character which indicates the type of format to use (one of 201.Cm diouxXfFeEgGaAbcs ) . 202.El 203.Pp 204A field width or precision may be 205.Ql \&* 206instead of a digit string. 207In this case an 208.Ar argument 209supplies the field width or precision. 210.Pp 211The format characters and their meanings are: 212.Bl -tag -width Ds 213.It Cm diouXx 214The 215.Ar argument 216is printed as a signed decimal 217.Pq Cm d No or Cm i , 218unsigned octal, unsigned decimal, 219or unsigned hexadecimal 220.Pq Cm x No or Cm X , 221respectively. 222.It Cm fF 223The 224.Ar argument 225is printed in the style 226.Sm off 227.Pf [\-]ddd Cm \&. No ddd 228.Sm on 229where the number of d's 230after the decimal point is equal to the precision specification for 231the argument. 232If the precision is missing, 6 digits are given; if the precision 233is explicitly 0, no digits and no decimal point are printed. 234.Pp 235If the argument is infinity, it will be converted to [-]inf 236.Pq Cm f 237or [-]INF 238.Pq Cm F , 239respectively. 240If the argument is not-a-number (NaN), it will be converted to 241[-]nan 242.Pq Cm f 243or [-]NAN 244.Pq Cm F , 245respectively. 246.It Cm eE 247The 248.Ar argument 249is printed in the style 250.Sm off 251.Pf [\-]d Cm \&. No ddd Cm e No \(+-dd 252.Sm on 253where there 254is one digit before the decimal point and the number after is equal to 255the precision specification for the argument; when the precision is 256missing, 6 digits are produced. 257An upper-case 258.Sq E 259is used for an 260.Cm E 261format. 262.Pp 263If the argument is infinity, it will be converted to [-]inf 264.Pq Cm e 265or [-]INF 266.Pq Cm E , 267respectively. 268If the argument is not-a-number (NaN), it will be converted to 269[-]nan 270.Pq Cm e 271or [-]NAN 272.Pq Cm E , 273respectively. 274.It Cm gG 275The 276.Ar argument 277is printed in style 278.Cm f 279or in style 280.Cm e 281.Pq Cm E 282whichever gives full precision in minimum space. 283.Pp 284If the argument is infinity, it will be converted to [-]inf 285.Pq Cm g 286or [-]INF 287.Pq Cm G , 288respectively. 289If the argument is not-a-number (NaN), it will be converted to 290[-]nan 291.Pq Cm g 292or [-]NAN 293.Pq Cm G , 294respectively. 295.It Cm aA 296The 297.Ar argument 298is printed in style 299.Sm off 300.Pf [\-]0xh Cm \&. No hhh Cm p No [\(+-]d 301.Sm on 302where there is one digit before the hexadecimal point and the number 303after is equal to the precision specification for the argument. 304When the precision is missing, enough digits are produced to convey 305the argument's exact double-precision floating-point representation. 306.Pp 307If the argument is infinity, it will be converted to [-]inf 308.Pq Cm a 309or [-]INF 310.Pq Cm A , 311respectively. 312If the argument is not-a-number (NaN), it will be converted to 313[-]nan 314.Pq Cm a 315or [-]NAN 316.Pq Cm A , 317respectively. 318.It Cm b 319Characters from the string 320.Ar argument 321are printed with backslash-escape sequences expanded. 322In the 323.Ar argument , 324ASCII characters can be octally encoded either as 325.Cm \e0 Ns Ar num 326or as 327.Cm \e Ns Ar num 328like in the 329.Ar format 330string. 331If the 332.Ar argument 333contains the special escape sequence 334.Cm \ec , 335this escape sequence is discarded together with 336all remaining characters in this argument, all further arguments, 337and all remaining characters in the 338.Ar format 339string. 340.It Cm c 341The first character of 342.Ar argument 343is printed. 344.It Cm s 345Characters from the string 346.Ar argument 347are printed until the end is reached or until the number of bytes 348indicated by the precision specification is reached; however if the 349precision is 0 or missing, all characters in the string are printed. 350.It Cm \&% 351Print a 352.Ql \&% ; 353no argument is used. 354.El 355.Pp 356In no case does a non-existent or small field width cause truncation of 357a field; padding takes place only if the specified field width exceeds 358the actual width. 359.Sh EXIT STATUS 360.Ex -std printf 361.Sh EXAMPLES 362Convert a hexadecimal value to decimal and print it out: 363.Pp 364.Dl $ printf \&"%d\en\&" 0x20 365.Pp 366Print the decimal representation of the character 'a' (see 367.Xr ascii 7 ) : 368.Pp 369.Dl $ printf \&"%d\en\&" \e'a 370.Sh SEE ALSO 371.Xr echo 1 , 372.Xr printf 3 373.Sh STANDARDS 374The 375.Nm 376utility is compliant with the 377.St -p1003.1-2008 378specification, but in order to produce predictable output 379it deliberately ignores the 380.Xr locale 1 381and always operates as if 382.Ev LC_ALL Ns =C 383were set. 384.Pp 385The escape sequences 386.Cm \ee 387and 388.Cm \e' , 389as well as omitting the leading digit 390.Cm 0 391from 392.Cm \e0 Ns Ar num 393octal escape sequences in 394.Cm %b 395arguments, are extensions to that specification. 396.Sh HISTORY 397The 398.Nm 399command appeared in 400.Bx 4.3 Reno . 401.Sh CAVEATS 402It is important never to pass a string with user-supplied data as a 403format without using 404.Ql %s . 405An attacker can put format specifiers in the string to mangle your stack, 406leading to a possible security hole. 407.Pp 408Always be sure to use the proper secure idiom: 409.Bd -literal -offset indent 410printf "%s" "$STRING" 411.Ed 412.Sh BUGS 413Since arguments are translated from ASCII to floating-point, 414and then back again, floating-point precision may be lost. 415