/usr.bin/printf/printf.1

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 31.\"	@(#)printf.1	8.1 (Berkeley) 6/6/93
 32.\" $FreeBSD$
 33.\"
 34.Dd May 28, 2011
 35.Dt PRINTF 1
 36.Os
 37.Sh NAME
 38.Nm printf
 39.Nd formatted output
 40.Sh SYNOPSIS
 41.Nm
 42.Ar format Op Ar arguments ...
 43.Sh DESCRIPTION
 44The
 45.Nm
 46utility formats and prints its arguments, after the first, under control
 47of the
 48.Ar format .
 49The
 50.Ar format
 51is a character string which contains three types of objects: plain characters,
 52which are simply copied to standard output, character escape sequences which
 53are converted and copied to the standard output, and format specifications,
 54each of which causes printing of the next successive
 55.Ar argument .
 56.Pp
 57The
 58.Ar arguments
 59after the first are treated as strings if the corresponding format is
 60either
 61.Cm c , b
 62or
 63.Cm s ;
 64otherwise it is evaluated as a C constant, with the following extensions:
 65.Pp
 66.Bl -bullet -offset indent -compact
 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
 71character code of the next character.
 72.El
 73.Pp
 74The format string is reused as often as necessary to satisfy the
 75.Ar arguments .
 76Any extra format specifications are evaluated with zero or the null
 77string.
 78.Pp
 79Character escape sequences are in backslash notation as defined in the
 80.St -ansiC ,
 81with extensions.
 82The characters and their meanings
 83are as follows:
 84.Pp
 85.Bl -tag -width Ds -offset indent -compact
 86.It Cm \ea
 87Write a <bell> character.
 88.It Cm \eb
 89Write a <backspace> character.
 90.It Cm \ec
 91Ignore remaining characters in this string.
 92.It Cm \ef
 93Write a <form-feed> character.
 94.It Cm \en
 95Write a <new-line> character.
 96.It Cm \er
 97Write a <carriage return> character.
 98.It Cm \et
 99Write a <tab> character.
100.It Cm \ev
101Write a <vertical tab> character.
102.It Cm \e\'
103Write a <single quote> character.
104.It Cm \e\e
105Write a backslash character.
106.It Cm \e Ns Ar num
107Write a byte whose
108value is the 1-, 2-, or 3-digit
109octal number
110.Ar num .
111Multibyte characters can be constructed using multiple
112.Cm \e Ns Ar num
113sequences.
114.El
115.Pp
116Each format specification is introduced by the percent character
117(``%'').
118The remainder of the format specification includes,
119in the following order:
120.Bl -tag -width Ds
121.It "Zero or more of the following flags:"
122.Bl -tag -width Ds
123.It Cm #
124A `#' character
125specifying that the value should be printed in an ``alternate form''.
126For
127.Cm b , c , d , s
128and
129.Cm u
130formats, this option has no effect.
131For the
132.Cm o
133formats the precision of the number is increased to force the first
134character of the output string to a zero.
135For the
136.Cm x
137.Pq Cm X
138format, a non-zero result has the string
139.Li 0x
140.Pq Li 0X
141prepended to it.
142For
143.Cm a , A , e , E , f , F , g
144and
145.Cm G
146formats, the result will always contain a decimal point, even if no
147digits follow the point (normally, a decimal point only appears in the
148results of those formats if a digit follows the decimal point).
149For
150.Cm g
151and
152.Cm G
153formats, trailing zeros are not removed from the result as they
154would otherwise be;
155.It Cm \&\-
156A minus sign `\-' which specifies
157.Em left adjustment
158of the output in the indicated field;
159.It Cm \&+
160A `+' character specifying that there should always be
161a sign placed before the number when using signed formats.
162.It Sq \&\ \&
163A space specifying that a blank should be left before a positive number
164for a signed format.
165A `+' overrides a space if both are used;
166.It Cm \&0
167A zero `0' character indicating that zero-padding should be used
168rather than blank-padding.
169A `\-' overrides a `0' if both are used;
170.El
171.It "Field Width:"
172An optional digit string specifying a
173.Em field width ;
174if the output string has fewer bytes than the field width it will
175be blank-padded on the left (or right, if the left-adjustment indicator
176has been given) to make up the field width (note that a leading zero
177is a flag, but an embedded zero is part of a field width);
178.It Precision:
179An optional period,
180.Sq Cm \&.\& ,
181followed by an optional digit string giving a
182.Em precision
183which specifies the number of digits to appear after the decimal point,
184for
185.Cm e
186and
187.Cm f
188formats, or the maximum number of bytes to be printed
189from a string; if the digit string is missing, the precision is treated
190as zero;
191.It Format:
192A character which indicates the type of format to use (one of
193.Cm diouxXfFeEgGaAcsb ) .
194The uppercase formats differ from their lowercase counterparts only in
195that the output of the former is entirely in uppercase.
196The floating-point format specifiers
197.Pq Cm fFeEgGaA
198may be prefixed by an
199.Cm L
200to request that additional precision be used, if available.
201.El
202.Pp
203A field width or precision may be
204.Sq Cm \&*
205instead of a digit string.
206In this case an
207.Ar argument
208supplies the field width or precision.
209.Pp
210The format characters and their meanings are:
211.Bl -tag -width Fl
212.It Cm diouXx
213The
214.Ar argument
215is printed as a signed decimal (d or i), unsigned octal, unsigned decimal,
216or unsigned hexadecimal (X or x), respectively.
217.It Cm fF
218The
219.Ar argument
220is printed in the style `[\-]ddd.ddd' where the number of d's
221after the decimal point is equal to the precision specification for
222the argument.
223If the precision is missing, 6 digits are given; if the precision
224is explicitly 0, no digits and no decimal point are printed.
225The values \*[If] and \*[Na] are printed as
226.Ql inf
227and
228.Ql nan ,
229respectively.
230.It Cm eE
231The
232.Ar argument
233is printed in the style
234.Cm e
235.Sm off
236.Sq Op - Ar d.ddd No \(+- Ar dd
237.Sm on
238where there
239is one digit before the decimal point and the number after is equal to
240the precision specification for the argument; when the precision is
241missing, 6 digits are produced.
242The values \*[If] and \*[Na] are printed as
243.Ql inf
244and
245.Ql nan ,
246respectively.
247.It Cm gG
248The
249.Ar argument
250is printed in style
251.Cm f
252.Pq Cm F
253or in style
254.Cm e
255.Pq Cm E
256whichever gives full precision in minimum space.
257.It Cm aA
258The
259.Ar argument
260is printed in style
261.Sm off
262.Sq Op - Ar h.hhh No \(+- Li p Ar d
263.Sm on
264where there is one digit before the hexadecimal point and the number
265after is equal to the precision specification for the argument;
266when the precision is missing, enough digits are produced to convey
267the argument's exact double-precision floating-point representation.
268The values \*[If] and \*[Na] are printed as
269.Ql inf
270and
271.Ql nan ,
272respectively.
273.It Cm c
274The first byte of
275.Ar argument
276is printed.
277.It Cm s
278Bytes from the string
279.Ar argument
280are printed until the end is reached or until the number of bytes
281indicated by the precision specification is reached; however if the
282precision is 0 or missing, the string is printed entirely.
283.It Cm b
284As for
285.Cm s ,
286but interpret character escapes in backslash notation in the string
287.Ar argument .
288The permitted escape sequences are slightly different in that
289octal escapes are
290.Cm \e0 Ns Ar num
291instead of
292.Cm \e Ns Ar num .
293.It Cm \&%
294Print a `%'; no argument is used.
295.El
296.Pp
297The decimal point
298character is defined in the program's locale (category
299.Dv LC_NUMERIC ) .
300.Pp
301In no case does a non-existent or small field width cause truncation of
302a field; padding takes place only if the specified field width exceeds
303the actual width.
304.Pp
305Some shells may provide a builtin
306.Nm
307command which is similar or identical to this utility.
308Consult the
309.Xr builtin 1
310manual page.
311.Sh EXIT STATUS
312.Ex -std
313.Sh COMPATIBILITY
314The traditional
315.Bx
316behavior of converting arguments of numeric formats not beginning
317with a digit to the
318.Tn ASCII
319code of the first character is not supported.
320.Sh SEE ALSO
321.Xr builtin 1 ,
322.Xr echo 1 ,
323.Xr sh 1 ,
324.Xr printf 3
325.Sh STANDARDS
326The
327.Nm
328command is expected to be compatible with the
329.St -p1003.2
330specification.
331.Sh HISTORY
332The
333.Nm
334command appeared in
335.Bx 4.3 Reno .
336It is modeled
337after the standard library function,
338.Xr printf 3 .
339.Sh CAVEATS
340.Tn ANSI
341hexadecimal character constants were deliberately not provided.
342.Pp
343Trying to print a dash ("-") as the first character causes
344.Nm
345to interpret the dash as a program argument.
346.Nm --
347must be used before
348.Ar format .
349.Pp
350If the locale contains multibyte characters
351(such as UTF-8),
352the
353.Cm c
354format and
355.Cm b
356and
357.Cm s
358formats with a precision
359may not operate as expected.
360.Sh BUGS
361Since the floating point numbers are translated from
362.Tn ASCII
363to floating-point and
364then back again, floating-point precision may be lost.
365(By default, the number is translated to an IEEE-754 double-precision
366value before being printed.
367The
368.Cm L
369modifier may produce additional precision, depending on the hardware platform.)
370.Pp
371The escape sequence \e000 is the string terminator.
372When present in the argument for the
373.Cm b
374format, the argument will be truncated at the \e000 character.
375.Pp
376Multibyte characters are not recognized in format strings (this is only
377a problem if
378.Ql %
379can appear inside a multibyte character).