PRINTF(1) FreeBSD General Commands Manual PRINTF(1)
NAME
printf - formatted output
SYNOPSIS
printf format [arguments ...]
DESCRIPTION
The printf 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.
\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 and u
formats, this option has no effect. For the o formats
the precision of the number is increased to force the
first character of the output string to a zero. For the
x (X) format, a non-zero result has the string 0x (0X)
prepended to it. For a, A, e, E, f, F, g and G 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). For g and G 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, for e and f 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 an L 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 style e (E)
whichever gives full precision in minimum space.
aA The argument is printed in style `[-h.hhh+-pd]' 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
\0num instead of \num and that an additional escape sequence
\c stops further output from this printf invocation.
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.
EXAMPLES
Print the string "hello":
$ printf "%s\n" hello
hello
Same as above, but notice that the format string is not quoted and hence
we do not get the expected behavior:
$ printf %s\n hello
hellon$
Print arguments forcing sign only for the first argument:
$ printf "%+d\n%d\n%d\n" 1 -2 13
+1
-2
13
Same as above, but the single format string will be applied to the three
arguments:
$ printf "%+d\n" 1 -2 13
+1
-2
+13
Print number using only two digits after the decimal point:
$ printf "%.2f\n" 31.7456
31.75
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
builtin(1), echo(1), sh(1), printf(3)
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).
FreeBSD 13.1-RELEASE-p6 July 1, 2020 FreeBSD 13.1-RELEASE-p6
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