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PRINTF(1) NetBSD General Commands Manual PRINTF(1)
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printf -- formatted output
printf format [arguments ...]
printf 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 b, B, c, or s; otherwise it is evaluated as a C con-
stant, with the following extensions:
ˇ A leading plus or minus sign is allowed.
ˇ If the leading character is a single or double quote, the value
is the ASCII 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 ANSI
X3.159-1989 (``ANSI C89''). The characters and their meanings are as
\e Write an <escape> character.
\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 <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 (``%'').
The remainder of the format specification includes, in the following
Zero or more of the following flags:
# A `#' character specifying that the value should be
printed in an ``alternative form''. For b, c, d, and s
formats, this option has no effect. For the o format 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 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 fol-
lows the decimal point). For g and G formats, trailing
zeros are not removed from the result as they would oth-
- 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;
An optional digit string specifying a field width; if the output
string has fewer characters than the field width it will be
blank-padded on the left (or right, if the left-adjustment indi-
cator 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
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 num-
ber of characters to be printed from a string (b, B, and s for-
mats); if the digit string is missing, the precision is treated
A character which indicates the type of format to use (one of
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, 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 preci-
sion 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 (NaN), then ``inf'' (or ``nan'')
is printed for f format, and ``INF'' (or ``NAN'') for F for-
eE The argument is printed in the style [-]d.dddeądd 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 back-
slash-escape sequences expanded.
The following additional backslash-escape sequences are sup-
\c Causes printf to ignore any remaining characters in
the string operand containing it, any remaining
string operands, and any additional characters in the
\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 character c with the 8th bit set. Gener-
ates characters `\241' through `\376`.
\M^c Write the control character c with the 8th bit set.
Generates characters `\200' through `\237`, and
`\377' (from `\M^?').
B Characters from the string argument are printed with unprint-
able characters backslash-escaped using the
`\c',`\^c',`\M-c'or `\M^c', formats described above.
c The first character of argument is printed.
s Characters from the string argument are printed until the end
is reached or until the number of characters indicated by the
precision specification is reached; if the precision is omit-
ted, all characters in the string are printed.
% Print a `%'; no argument is used.
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
If the first character of format is a dash, format must be preceded by a
word consisting of two dashes (--) to prevent it from being interpreted
as an option string.
The printf utility exits 0 on success, and >0 if an error occurs.
echo(1), printf(3), vis(3), printf(9)
The printf utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
Support for the floating point formats and `*' as a field width and pre-
cision are optional in POSIX.
The behaviour of the %B format and the \', \", \xxx, \e and \[M][-|^]c
escape sequences are undefined in POSIX.
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 are restricted to, and should be speci-
fied as, two character constants. This is contrary to the ISO C standard
but does guarantee detection of the end of the constant.
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 inter-
nal 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, 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 for-
mat. For example, the following command outputs the character whose code
is 0x0A, which is a newline in ASCII:
printf "$(printf "\\%o" "0x0A")"
NetBSD 9.0 August 31, 2018 NetBSD 9.0