NAME
printf
—
formatted output
SYNOPSIS
printf |
format [arguments ...] |
DESCRIPTION
Theprintf
utility formats and prints its arguments,
after the first, under control of the format. The
format is a character string which contains three types
of objects: plain characters, which are simply copied to standard output,
character escape sequences which are converted and copied to the standard
output, and format specifications, each of which causes printing of the next
successive argument.
The arguments after the first are treated as
strings if the corresponding format is either c
,
b
or s
; otherwise it is
evaluated as a C constant, with the following extensions:
- A leading plus or minus sign is allowed.
- If the leading character is a single or double quote, the value is the character code of the next character.
The format string is reused as often as necessary to satisfy the arguments. Any extra format specifications are evaluated with zero or the null string.
Character escape sequences are in backslash notation as defined in the ANSI X3.159-1989 (“ANSI C89”), with extensions. The characters and their meanings are as follows:
\a
- Write a <bell> character.
\b
- Write a <backspace> character.
\c
- Ignore remaining characters in this string.
\f
- Write a <form-feed> character.
\n
- Write a <new-line> character.
\r
- Write a <carriage return> character.
\t
- Write a <tab> character.
\v
- Write a <vertical tab> character.
\´
- Write a <single quote> character.
\\
- Write a backslash character.
\
num- Write a byte whose value is the 1-, 2-, or 3-digit octal number
num. Multibyte characters can be constructed using
multiple
\
num sequences.
Each format specification is introduced by the percent character (``%''). The remainder of the format specification includes, in the following order:
- Zero or more of the following flags:
-
#
- A `#' character specifying that the value should be printed in an
``alternate form''. For
b
,c
,d
,s
andu
formats, this option has no effect. For theo
formats the precision of the number is increased to force the first character of the output string to a zero. For thex
(X
) format, a non-zero result has the string0x
(0X
) prepended to it. Fora
,A
,e
,E
,f
,F
,g
andG
formats, the result will always contain a decimal point, even if no digits follow the point (normally, a decimal point only appears in the results of those formats if a digit follows the decimal point). Forg
andG
formats, trailing zeros are not removed from the result as they would otherwise be; -
- A minus sign `-' which specifies left adjustment of the output in the indicated field;
+
- A `+' character specifying that there should always be a sign placed before the number when using signed formats.
- ‘ ’
- A space specifying that a blank should be left before a positive number for a signed format. A `+' overrides a space if both are used;
0
- A zero `0' character indicating that zero-padding should be used rather than blank-padding. A `-' overrides a `0' if both are used;
- Field Width:
- An optional digit string specifying a field width; if the output string has fewer bytes than the field width it will be blank-padded on the left (or right, if the left-adjustment indicator has been given) to make up the field width (note that a leading zero is a flag, but an embedded zero is part of a field width);
- Precision:
- An optional period, ‘
.
’, followed by an optional digit string giving a precision which specifies the number of digits to appear after the decimal point, fore
andf
formats, or the maximum number of bytes to be printed from a string; if the digit string is missing, the precision is treated as zero; - Format:
- A character which indicates the type of format to use (one of
diouxXfFeEgGaAcsb
). The uppercase formats differ from their lowercase counterparts only in that the output of the former is entirely in uppercase. The floating-point format specifiers (fFeEgGaA
) may be prefixed by anL
to request that additional precision be used, if available.
A field width or precision may be
‘*
’ instead of a digit string. In this
case an argument supplies the field width or
precision.
The format characters and their meanings are:
diouXx
- The argument is printed as a signed decimal (d or i), unsigned octal, unsigned decimal, or unsigned hexadecimal (X or x), respectively.
fF
- The argument is printed in the style `[-]ddd.ddd'
where the number of d's after the decimal point is equal to the precision
specification for the argument. If the precision is missing, 6 digits are
given; if the precision is explicitly 0, no digits and no decimal point
are printed. The values infinity and NaN are printed as
‘
inf
’ and ‘nan
’, respectively. eE
- The argument is printed in the style
e
‘[-d.ddd±dd]’ where there is one digit before the decimal point and the number after is equal to the precision specification for the argument; when the precision is missing, 6 digits are produced. The values infinity and NaN are printed as ‘inf
’ and ‘nan
’, respectively. gG
- The argument is printed in style
f
(F
) or in stylee
(E
) whichever gives full precision in minimum space. aA
- The argument is printed in style
‘[-h.hhh±
p
d]’ where there is one digit before the hexadecimal point and the number after is equal to the precision specification for the argument; when the precision is missing, enough digits are produced to convey the argument's exact double-precision floating-point representation. The values infinity and NaN are printed as ‘inf
’ and ‘nan
’, respectively. c
- The first byte of argument is printed.
s
- Bytes from the string argument are printed until the end is reached or until the number of bytes indicated by the precision specification is reached; however if the precision is 0 or missing, the string is printed entirely.
b
- As for
s
, but interpret character escapes in backslash notation in the string argument. The permitted escape sequences are slightly different in that octal escapes are\0
num instead of\
num. n$
- Allows reordering of the output according to argument.
%
- Print a `%'; no argument is used.
The decimal point character is defined in the program's locale
(category LC_NUMERIC
).
In no case does a non-existent or small field width cause truncation of a field; padding takes place only if the specified field width exceeds the actual width.
Some shells may provide a builtin printf
command which is similar or identical to this utility. Consult the
builtin(1) manual page.
EXIT STATUS
The printf
utility exits 0 on
success, and >0 if an error occurs.
COMPATIBILITY
The traditional BSD behavior of converting arguments of numeric formats not beginning with a digit to the ASCII code of the first character is not supported.
SEE ALSO
STANDARDS
The printf
command is expected to be
compatible with the IEEE Std 1003.2
(“POSIX.2”) specification.
HISTORY
The printf
command appeared in
4.3BSD-Reno. It is modeled after the standard
library function,
printf(3).
CAVEATS
ANSI hexadecimal character constants were deliberately not provided.
Trying to print a dash ("-") as the first character
causes printf
to interpret the dash as a program
argument. --
must be used before
format.
If the locale contains multibyte characters (such as UTF-8), the
c
format and b
and
s
formats with a precision may not operate as
expected.
BUGS
Since the floating point numbers are translated from ASCII to
floating-point and then back again, floating-point precision may be lost.
(By default, the number is translated to an IEEE-754 double-precision value
before being printed. The L
modifier may produce
additional precision, depending on the hardware platform.)
The escape sequence \000 is the string terminator. When present in
the argument for the b
format, the argument will be
truncated at the \000 character.
Multibyte characters are not recognized in format strings (this is
only a problem if ‘%
’ can appear
inside a multibyte character).