printf.1 (10108B)
1 .\" $OpenBSD: src/usr.bin/printf/printf.1,v 1.27 2014/05/25 07:36:36 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 13 2014 $ 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 47 formats and prints its arguments, after the first, under control 48 of the 49 .Ar format . 50 The 51 .Ar format 52 is a character string which contains three types of objects: plain characters, 53 which are simply copied to standard output, character escape sequences which 54 are converted and copied to the standard output, and format specifications, 55 each of which causes printing of the next successive 56 .Ar argument . 57 .Pp 58 The arguments after the first are treated as strings 59 if the corresponding format is 60 .Cm b , 61 .Cm c 62 or 63 .Cm s ; 64 otherwise it is evaluated as a C constant, with the following extensions: 65 .Bl -bullet -offset indent 66 .It 67 A leading plus or minus sign is allowed. 68 .It 69 If the leading character is a single or double quote, the value is the 70 .Tn ASCII 71 code of the next character. 72 .El 73 .Pp 74 The format string is reused as often as necessary to satisfy the arguments. 75 Any extra format specifications are evaluated with zero or the null 76 string. 77 .Pp 78 Character escape sequences are in backslash notation as defined in 79 .St -ansiC . 80 The characters and their meanings are as follows: 81 .Pp 82 .Bl -tag -width Ds -offset indent -compact 83 .It Cm \ee 84 Write an <escape> character. 85 .It Cm \ea 86 Write a <bell> character. 87 .It Cm \eb 88 Write a <backspace> character. 89 .It Cm \ef 90 Write a <form-feed> character. 91 .It Cm \en 92 Write a <new-line> character. 93 .It Cm \er 94 Write a <carriage return> character. 95 .It Cm \et 96 Write a <tab> character. 97 .It Cm \ev 98 Write a <vertical tab> character. 99 .It Cm \e\' 100 Write a <single quote> character. 101 .It Cm \e\e 102 Write a backslash character. 103 .It Cm \e Ns Ar num 104 Write an 8-bit character whose 105 .Tn ASCII 106 value is the 1-, 2-, or 3-digit 107 octal number 108 .Ar num . 109 .El 110 .Pp 111 Each format specification is introduced by the percent 112 .Pq Sq \&% 113 character. 114 The remainder of the format specifiers include, 115 in the following order: 116 .Bl -tag -width Ds 117 .It "Zero or more of the following flags:" 118 .Bl -tag -width Ds 119 .It Cm # 120 Specifies that the value should be printed in an 121 .Dq alternate form . 122 For the 123 .Cm o 124 format the precision of the number is increased to force the first 125 character of the output string to a zero. 126 For the 127 .Cm x 128 .Pq Cm X 129 format, a non-zero result has the string 130 .Li 0x 131 .Pq Li 0X 132 prepended to it. 133 For 134 .Cm a , 135 .Cm A , 136 .Cm e , 137 .Cm E , 138 .Cm f , 139 .Cm F , 140 .Cm g , 141 and 142 .Cm G 143 formats, the result will always contain a decimal point, even if no 144 digits follow the point (normally, a decimal point only appears in the 145 results of those formats if a digit follows the decimal point). 146 For 147 .Cm g 148 and 149 .Cm G 150 formats, trailing zeros are not removed from the result as they 151 would otherwise be. 152 For all other formats, behaviour is undefined. 153 .It Cm \&\- 154 Specifies the 155 .Em left adjustment 156 of the output in the indicated field. 157 .It Cm \&+ 158 Specifies that there should always be 159 a sign placed before the number when using signed formats. 160 .It Sq \&\ \& 161 A space specifies that a blank should be left before a positive number 162 for a signed format. 163 A 164 .Ql + 165 overrides a space if both are used. 166 .It Cm \&0 167 A zero character specifies that zero-padding should be used 168 rather than blank-padding. 169 This flag is ignored if used with a precision 170 specifier and any of the 171 .Cm d , i , o , u , 172 or 173 .Cm x 174 .Pq Cm X 175 formats. 176 A 177 .Ql \&- 178 overrides a 179 .Ql \&0 180 if both are used. 181 .El 182 .It "Field Width:" 183 An optional digit string specifying a 184 .Em field width ; 185 if the output string has fewer characters than the field width it will 186 be blank-padded on the left (or right, if the left-adjustment indicator 187 has been given) to make up the field width (note that a leading zero 188 is a flag, but an embedded zero is part of a field width). 189 .It Precision: 190 An optional period 191 .Pq Sq \&. , 192 followed by an optional digit string giving a 193 .Em precision 194 which specifies the number of digits to appear after the decimal point, 195 for 196 .Cm e 197 and 198 .Cm f 199 formats, or the maximum number of characters to be printed 200 from a string; if the digit string is missing, the precision is treated 201 as zero. 202 .It Format: 203 A character which indicates the type of format to use (one of 204 .Cm diouxXfFeEgGaAbcs ) . 205 .El 206 .Pp 207 A field width or precision may be 208 .Ql \&* 209 instead of a digit string. 210 In this case an 211 .Ar argument 212 supplies the field width or precision. 213 .Pp 214 The format characters and their meanings are: 215 .Bl -tag -width Fl 216 .It Cm diouXx 217 The 218 .Ar argument 219 is printed as a signed decimal 220 .Pq Cm d No or Cm i , 221 unsigned octal, unsigned decimal, 222 or unsigned hexadecimal 223 .Pq Cm x No or Cm X , 224 respectively. 225 .It Cm fF 226 The 227 .Ar argument 228 is printed in the style 229 .Sm off 230 .Pf [\-]ddd Cm \&. No ddd 231 .Sm on 232 where the number of d's 233 after the decimal point is equal to the precision specification for 234 the argument. 235 If the precision is missing, 6 digits are given; if the precision 236 is explicitly 0, no digits and no decimal point are printed. 237 .Pp 238 If the argument is infinity, it will be converted to [-]inf 239 .Pq Cm f 240 or [-]INF 241 .Pq Cm F , 242 respectively. 243 If the argument is not-a-number (NaN), it will be converted to 244 [-]nan 245 .Pq Cm f 246 or [-]NAN 247 .Pq Cm F , 248 respectively. 249 .It Cm eE 250 The 251 .Ar argument 252 is printed in the style 253 .Sm off 254 .Pf [\-]d Cm \&. No ddd Cm e No \*(Pmdd 255 .Sm on 256 where there 257 is one digit before the decimal point and the number after is equal to 258 the precision specification for the argument; when the precision is 259 missing, 6 digits are produced. 260 An upper-case 261 .Sq E 262 is used for an 263 .Cm E 264 format. 265 .Pp 266 If the argument is infinity, it will be converted to [-]inf 267 .Pq Cm e 268 or [-]INF 269 .Pq Cm E , 270 respectively. 271 If the argument is not-a-number (NaN), it will be converted to 272 [-]nan 273 .Pq Cm e 274 or [-]NAN 275 .Pq Cm E , 276 respectively. 277 .It Cm gG 278 The 279 .Ar argument 280 is printed in style 281 .Cm f 282 or in style 283 .Cm e 284 .Pq Cm E 285 whichever gives full precision in minimum space. 286 .Pp 287 If the argument is infinity, it will be converted to [-]inf 288 .Pq Cm g 289 or [-]INF 290 .Pq Cm G , 291 respectively. 292 If the argument is not-a-number (NaN), it will be converted to 293 [-]nan 294 .Pq Cm g 295 or [-]NAN 296 .Pq Cm G , 297 respectively. 298 .It Cm aA 299 The 300 .Ar argument 301 is printed in style 302 .Sm off 303 .Pf [\-]0xh Cm \&. No hhh Cm p No [\*(Pm]d 304 .Sm on 305 where there is one digit before the hexadecimal point and the number 306 after is equal to the precision specification for the argument. 307 When the precision is missing, enough digits are produced to convey 308 the argument's exact double-precision floating-point representation. 309 .Pp 310 If the argument is infinity, it will be converted to [-]inf 311 .Pq Cm a 312 or [-]INF 313 .Pq Cm A , 314 respectively. 315 If the argument is not-a-number (NaN), it will be converted to 316 [-]nan 317 .Pq Cm a 318 or [-]NAN 319 .Pq Cm A , 320 respectively. 321 .It Cm b 322 Characters from the string 323 .Ar argument 324 are printed with backslash-escape sequences expanded. 325 .It Cm c 326 The first character of 327 .Ar argument 328 is printed. 329 .It Cm s 330 Characters from the string 331 .Ar argument 332 are printed until the end is reached or until the number of characters 333 indicated by the precision specification is reached; however if the 334 precision is 0 or missing, all characters in the string are printed. 335 .It Cm \&% 336 Print a 337 .Ql \&% ; 338 no argument is used. 339 .El 340 .Pp 341 In no case does a non-existent or small field width cause truncation of 342 a field; padding takes place only if the specified field width exceeds 343 the actual width. 344 .Sh EXIT STATUS 345 .Ex -std printf 346 .Sh EXAMPLES 347 Convert a hexadecimal value to decimal and print it out: 348 .Pp 349 .D1 Ic $ printf \&"%d\en\&" 0x20 350 .Pp 351 Print the decimal representation of the character 'a' (see 352 .Xr ascii 7 ) : 353 .Pp 354 .D1 Ic $ printf \&"%d\en\&" \e'a 355 .Sh SEE ALSO 356 .Xr echo 1 , 357 .Xr printf 3 358 .Sh STANDARDS 359 The 360 .Nm 361 utility is compliant with the 362 .St -p1003.1-2008 363 specification. 364 .Pp 365 The escape sequences \ee and \e' are extensions to that specification. 366 .Sh HISTORY 367 The 368 .Nm 369 command appeared in 370 .Bx 4.3 Reno . 371 .Sh CAVEATS 372 It is important never to pass a string with user-supplied data as a 373 format without using 374 .Ql %s . 375 An attacker can put format specifiers in the string to mangle your stack, 376 leading to a possible security hole. 377 .Pp 378 Always be sure to use the proper secure idiom: 379 .Bd -literal -offset indent 380 printf "%s" "$STRING" 381 .Ed 382 .Sh BUGS 383 Since arguments are translated from 384 .Tn ASCII 385 to floating-point, and 386 then back again, floating-point precision may be lost.