printf/printf.1

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  35 .\"     @(#)printf.1    8.1 (Berkeley) 6/6/93
  36 .\" $FreeBSD: src/usr.bin/printf/printf.1,v 1.34 2005/06/14 11:50:52 ru Exp $
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  38 .Dd April 14, 2005
  39 .Dt PRINTF 1
  40 .Os
  41 .Sh NAME
  42 .Nm printf
  43 .Nd formatted output
  44 .Sh SYNOPSIS
  45 .Nm
  46 .Ar format Op Ar arguments ...
  47 .Sh DESCRIPTION
  48 The
  49 .Nm
  50 utility formats and prints its arguments, after the first, under control
  51 of the
  52 .Ar format .
  53 The
  54 .Ar format
  55 is a character string which contains three types of objects: plain characters,
  56 which are simply copied to standard output, character escape sequences which
  57 are converted and copied to the standard output, and format specifications,
  58 each of which causes printing of the next successive
  59 .Ar argument .
  60 .Pp
  61 The
  62 .Ar arguments
  63 after the first are treated as strings if the corresponding format is
  64 either
  65 .Cm c , b
  66 or
  67 .Cm s ;
  68 otherwise it is evaluated as a C constant, with the following extensions:
  69 .Pp
  70 .Bl -bullet -offset indent -compact
  71 .It
  72 A leading plus or minus sign is allowed.
  73 .It
  74 If the leading character is a single or double quote, the value is the
  75 .Tn ASCII
  76 code of the next character.
  77 .El
  78 .Pp
  79 The format string is reused as often as necessary to satisfy the
  80 .Ar arguments .
  81 Any extra format specifications are evaluated with zero or the null
  82 string.
  83 .Pp
  84 Character escape sequences are in backslash notation as defined in the
  85 .St -ansiC ,
  86 with extensions.
  87 The characters and their meanings
  88 are as follows:
  89 .Pp
  90 .Bl -tag -width Ds -offset indent -compact
  91 .It Cm \ea
  92 Write a <bell> character.
  93 .It Cm \eb
  94 Write a <backspace> character.
  95 .It Cm \ec
  96 Ignore remaining characters in this string.
  97 .It Cm \ef
  98 Write a <form-feed> character.
  99 .It Cm \en
 100 Write a <new-line> character.
 101 .It Cm \er
 102 Write a <carriage return> character.
 103 .It Cm \et
 104 Write a <tab> character.
 105 .It Cm \ev
 106 Write a <vertical tab> character.
 107 .It Cm \e\'
 108 Write a <single quote> character.
 109 .It Cm \e\e
 110 Write a backslash character.
 111 .It Cm \e Ns Ar num
 112 .It Cm \e0 Ns Ar num
 113 Write an 8-bit character whose
 114 .Tn ASCII
 115 value is the 1-, 2-, or 3-digit
 116 octal number
 117 .Ar num .
 118 .El
 119 .Pp
 120 Each format specification is introduced by the percent character
 121 (``%'').
 122 The remainder of the format specification includes,
 123 in the following order:
 124 .Bl -tag -width Ds
 125 .It "Zero or more of the following flags:"
 126 .Bl -tag -width Ds
 127 .It Cm #
 128 A `#' character
 129 specifying that the value should be printed in an ``alternate form''.
 130 For
 131 .Cm c , d ,
 132 and
 133 .Cm s ,
 134 formats, this option has no effect.
 135 For the
 136 .Cm o
 137 formats the precision of the number is increased to force the first
 138 character of the output string to a zero.
 139 For the
 140 .Cm x
 141 .Pq Cm X
 142 format, a non-zero result has the string
 143 .Li 0x
 144 .Pq Li 0X
 145 prepended to it.
 146 For
 147 .Cm e , E , f , g ,
 148 and
 149 .Cm G ,
 150 formats, the result will always contain a decimal point, even if no
 151 digits follow the point (normally, a decimal point only appears in the
 152 results of those formats if a digit follows the decimal point).
 153 For
 154 .Cm g
 155 and
 156 .Cm G
 157 formats, trailing zeros are not removed from the result as they
 158 would otherwise be;
 159 .It Cm \&\-
 160 A minus sign `\-' which specifies
 161 .Em left adjustment
 162 of the output in the indicated field;
 163 .It Cm \&+
 164 A `+' character specifying that there should always be
 165 a sign placed before the number when using signed formats.
 166 .It Sq \&\ \&
 167 A space specifying that a blank should be left before a positive number
 168 for a signed format.
 169 A `+' overrides a space if both are used;
 170 .It Cm \&0
 171 A zero `0' character indicating that zero-padding should be used
 172 rather than blank-padding.
 173 A `\-' overrides a `0' if both are used;
 174 .El
 175 .It "Field Width:"
 176 An optional digit string specifying a
 177 .Em field width ;
 178 if the output string has fewer characters than the field width it will
 179 be blank-padded on the left (or right, if the left-adjustment indicator
 180 has been given) to make up the field width (note that a leading zero
 181 is a flag, but an embedded zero is part of a field width);
 182 .It Precision:
 183 An optional period,
 184 .Sq Cm \&.\& ,
 185 followed by an optional digit string giving a
 186 .Em precision
 187 which specifies the number of digits to appear after the decimal point,
 188 for
 189 .Cm e
 190 and
 191 .Cm f
 192 formats, or the maximum number of characters to be printed
 193 from a string; if the digit string is missing, the precision is treated
 194 as zero;
 195 .It Format:
 196 A character which indicates the type of format to use (one of
 197 .Cm diouxXfFeEgGaAcsb ) .
 198 The uppercase formats differ from their lowercase counterparts only in
 199 that the output of the former is entirely in uppercase.
 200 The floating-point format specifiers
 201 .Pq Cm fFeEgGaA
 202 may be prefixed by an
 203 .Cm L
 204 to request that additional precision be used, if available.
 205 .El
 206 .Pp
 207 A field width or precision may be
 208 .Sq Cm \&*
 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 (d or i), unsigned octal, unsigned decimal,
 220 or unsigned hexadecimal (X or x), respectively.
 221 .It Cm fF
 222 The
 223 .Ar argument
 224 is printed in the style `[\-]ddd.ddd' where the number of d's
 225 after the decimal point is equal to the precision specification for
 226 the argument.
 227 If the precision is missing, 6 digits are given; if the precision
 228 is explicitly 0, no digits and no decimal point are printed.
 229 The values \*[If] and \*[Na] are printed as
 230 .Ql inf
 231 and
 232 .Ql nan ,
 233 respectively.
 234 .It Cm eE
 235 The
 236 .Ar argument
 237 is printed in the style
 238 .Cm e
 239 .Sm off
 240 .Sq Op - Ar d.ddd No \(+- Ar dd
 241 .Sm on
 242 where there
 243 is one digit before the decimal point and the number after is equal to
 244 the precision specification for the argument; when the precision is
 245 missing, 6 digits are produced.
 246 The values \*[If] and \*[Na] are printed as
 247 .Ql inf
 248 and
 249 .Ql nan ,
 250 respectively.
 251 .It Cm gG
 252 The
 253 .Ar argument
 254 is printed in style
 255 .Cm f
 256 .Pq Cm F
 257 or in style
 258 .Cm e
 259 .Pq Cm E
 260 whichever gives full precision in minimum space.
 261 .It Cm aA
 262 The
 263 .Ar argument
 264 is printed in style
 265 .Sm off
 266 .Sq Op - Ar h.hhh No \(+- Li p Ar d
 267 .Sm on
 268 where there is one digit before the hexadecimal point and the number
 269 after is equal to the precision specification for the argument;
 270 when the precision is missing, enough digits are produced to convey
 271 the argument's exact double-precision floating-point representation.
 272 The values \*[If] and \*[Na] are printed as
 273 .Ql inf
 274 and
 275 .Ql nan ,
 276 respectively.
 277 .It Cm c
 278 The first character of
 279 .Ar argument
 280 is printed.
 281 .It Cm s
 282 Characters from the string
 283 .Ar argument
 284 are printed until the end is reached or until the number of characters
 285 indicated by the precision specification is reached; however if the
 286 precision is 0 or missing, all characters in the string are printed.
 287 .It Cm b
 288 As for
 289 .Cm s ,
 290 but interpret character escapes in backslash notation in the string
 291 .Ar argument .
 292 .It Cm \&%
 293 Print a `%'; no argument is used.
 294 .El
 295 .Pp
 296 The decimal point
 297 character is defined in the program's locale (category
 298 .Dv LC_NUMERIC ) .
 299 .Pp
 300 In no case does a non-existent or small field width cause truncation of
 301 a field; padding takes place only if the specified field width exceeds
 302 the actual width.
 303 .Sh EXIT STATUS
 304 .Ex -std
 305 .Sh COMPATIBILITY
 306 The traditional
 307 .Bx
 308 behavior of converting arguments of numeric formats not beginning
 309 with a digit to the
 310 .Tn ASCII
 311 code of the first character is not supported.
 312 .Sh SEE ALSO
 313 .Xr echo 1 ,
 314 .Xr printf 3
 315 .Sh STANDARDS
 316 The
 317 .Nm
 318 command is expected to be mostly compatible with the
 319 .St -p1003.2
 320 specification.
 321 .Sh HISTORY
 322 The
 323 .Nm
 324 command appeared in
 325 .Bx 4.3 Reno .
 326 It is modeled
 327 after the standard library function,
 328 .Xr printf 3 .
 329 .Sh BUGS
 330 Since the floating point numbers are translated from
 331 .Tn ASCII
 332 to floating-point and
 333 then back again, floating-point precision may be lost.
 334 (By default, the number is translated to an IEEE-754 double-precision
 335 value before being printed.
 336 The
 337 .Cm L
 338 modifier may produce additional precision, depending on the hardware platform.)
 339 .Pp
 340 .Tn ANSI
 341 hexadecimal character constants were deliberately not provided.
 342 .Pp
 343 The escape sequence \e000 is the string terminator.
 344 When present in the argument for the
 345 .Cm b
 346 format, the argument will be truncated at the \e000 character.
 347 .Pp
 348 Multibyte characters are not recognized in format strings (this is only
 349 a problem if
 350 .Ql %
 351 can appear inside a multibyte character).
 352 .Pp
 353 Parsing of - arguments is also somewhat different from
 354 .Xr printf 3 ,
 355 where unknown arguments are simply printed instead of being
 356 flagged as errors.