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PRINTF(1) General Commands Manual PRINTF(1)
NAME
printf - formatted output
SYNOPSIS
printf [-L] format [argument ...]
DESCRIPTION
printf formats and prints its arguments, 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. Each argument is used only once.
If the first character of format is a dash (`-'), format must (and always
may) be preceded by a word consisting of two dashes (`--') to prevent it
from being interpreted as an option string. See getopt(3).
The -L option causes all floating point values resulting from format
conversions to be printed using long double formats, rather than the
default double.
The arguments after the first are treated as strings if the corresponding
format is either b, B, c, or s; otherwise each 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, as part
of the argument rather than just quoting it for the shell, the
value is the code of the character following that quote
character. No further characters are permitted.
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 ANSI
X3.159-1989 ("ANSI C89"). The characters and their meanings are as
follows:
\a Write a <bell> character.
\b Write a <backspace> character.
\e Write an <escape> 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 <double quote> character.
\\ Write a backslash character.
\num Write an 8-bit character whose ASCII value is the 1-,
2-, or 3-digit octal number num.
\xXX Write an 8-bit character whose ASCII value is the 1- or
2-digit hexadecimal number XX.
Each format specification is introduced by the percent character (`%').
To produce a literal percent (`%') in the output, write the percent
character twice: (`%%'). This is not a format conversion, but a special
escape sequence, and consumes no arguments. The remainder of the format
specification includes, in the following order:
Zero or more of the following unordered flags:
# A `#' character specifying that the value should be
printed in an "alternative form". For b, c, C, d, and
s formats, this option has no effect. For the o
format the precision of the number is increased to
cause the first character of the numeric output string
to be a zero. For the x (X) format, a non-zero result
has the string `0x' (`0X') prepended to it. For 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 plus sign which specifies that there should always
be a sign (`+' or `-') placed before the number when
using signed formats;
` ' A <space> character which specifies that a space
should be left in the position a minus sign would
otherwise appear, before a non-negative number for a
signed format. A `+' overrides a <space> if both are
used;
0 A digit zero character which specifies that zero-
padding should be used rather than space-padding to
the left of right adjusted fields. In this case, a
sign (`+', `-' or ` '), if included, precedes the
padding. Padding to the right of left adjusted fields
always uses spaces. A `-' overrides a `0' if both are
used;
Specifying a flag more than once is not an error, but has no
additional effect.
Field Width:
An optional digit string specifying a field width; if the output
string has fewer bytes than the field width it will be 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 a zero appearing after another digit 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 (b, B, and s formats);
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
diouxXfFeEgGaAbBcCs).
A field width or precision may be `*' instead of a digit string. In this
case the next argument, preceding the value to be converted, supplies the
field width or precision. It must be an unsigned integer constant. If
both the field width and precision are `*' then two arguments are
required, with the field width preceding the precision, and the value to
be converted following those.
The format characters and their meanings are:
diouXx The argument, which must represent an integer constant, with
an optional leading plus or minus sign, is printed as a
signed decimal (d or i), unsigned octal (o), unsigned decimal
(u), or unsigned hexadecimal (X or x).
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. If
the number is Infinity, or Not-a-Number, then `inf' or `nan'
is printed for f format, and `INF' or `NAN' for F format.
eE The argument is printed in the style [-]d.ddde+-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. An upper-case `E' is used for an E format, and
upper-case for Infinity and NaN as for F format.
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 treated as a floating point number, for which
the underlying hexadecimal representation is printed. See
printf(3) for the details.
b Characters from the string argument are printed with
backslash-escape sequences expanded.
The following additional backslash-escape sequences are
supported:
\c Causes printf to ignore any remaining characters
in the string operand containing it, any
remaining operands, and any additional characters
in the format operand.
\0num Write an 8-bit character whose ASCII value is the
1-, 2-, or 3-digit octal number num.
\^c Write the control character c. Generates
characters `\000' through `\037', and `\177'
(from `\^?').
\M^c Write the control character c with the 8th bit
set. Generates characters `\200' through `\237',
and `\377' (from `\M^?').
\M-c Write the character c with the 8th bit set.
Generates characters `\240' through `\376'.
B Characters from the string argument are printed with
unprintable characters backslash-escaped using the `\c',
`\^c', `\M^c', or `\M-c' formats described above.
c The first character of the next argument is printed.
C The argument, which must represent an integer constant, with
an optional leading plus or minus sign, is treated as a wide
character code point, and printed.
s Characters from the string argument are printed until the end
is reached or until the number of bytes indicated by the
precision specification is reached; if the precision is
omitted, all characters in the string are printed.
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.
If an argument required by a format string is present, but is not in a
format expected by the format string conversion, a warning will be
printed to standard error, identifying the argument by number (1 is the
first after the format string) and usually also by content. In such a
case a value will still be produced, and printed, and processing will
continue, but printf will eventually exit with a failure status.
EXIT STATUS
The printf utility exits 0 on success, and >0 if an error occurs.
SEE ALSO
echo(1), printf(3), vis(3), printf(9)
STANDARDS
The printf utility conforms to IEEE Std 1003.1-2001 ("POSIX.1").
Support for the floating point formats and `*' as a field width and
precision are optional in POSIX.
The behaviour of the %B and %C formats and the \', \", \e, \xXX, and
\[M][-|^]c escape sequences are undefined in POSIX.
BUGS
Since the floating point numbers are translated from ASCII to floating-
point and then back again, floating-point precision may be lost.
Hexadecimal character constants given as escapes in strings are
restricted to, and should be specified as, two hexadecimal characters.
This is contrary to the ISO C standard but does guarantee detection of
the end of the constant.
NOTES
All formats which treat the argument as a number first convert the
argument from its external representation as a character string to an
internal numeric representation, and then apply the format to the
internal numeric representation, producing another external character
string representation. One might expect the %c format to do likewise,
but in fact it does not.
To convert a string representation of a decimal, octal, or hexadecimal
number into the corresponding character, using a portable invocation, two
nested printf invocations may be used, in which the inner invocation
converts the input to an octal string, and the outer invocation uses the
octal string as part of a format. For example, the following command
outputs the character whose code is 0x0a, which is a newline in ASCII:
printf "$(printf '\\%o' 0x0a)"
In this implementation of printf it is possible to achieve the same
result using one invocation:
printf %C 0x0a
NetBSD 11.99 November 24, 2024 NetBSD 11.99