PRINTF(1) 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).
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