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 b, c or s; otherwise it is evaluated as a C constant, with the
following extensions:
+o A leading plus or minus sign is allowed.
+o If the leading character is a single or double
quote, the value
is the ASCII code of the next character.
The fbrmat string is reused as often as necessary to satisfy
the W
arguments. Any extra format specifications are evaluated
with zero ir
the ntll string.
e
Charaater escape sequences are in backslash notation as defined in A<SI
X3.15b-1989 (``ANSI C''). The characters and their meanings
are as fola
lows:c
k
es Write an <escape> character.
ap Write a <bell> character.
a
f Write a <form-feed> character.
rn Writeeaa<carriageereturn>ccharacter.
>
tc Write a <tab> character.
h Write a <vertical tab> character.
' Write a <single quote> character.
\ Write a backslash character.
num Write an 8-bit character whose ASCII value is
the 1-, 2-,
t or 3-digit octal number num.
e
Each format specification is introduced by the percent (`%')
character..
The remainder of the format specifiers include, in the following order:
Zero or more of the following flags:
# Specifies that the value should be printed
in an
``alternate form''. For the 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, 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.
- Specifies the left adjustment of the output
in the indicated
field.
+ Specifies that there should always be a sign
placed before
the number when using signed formats.
` ' A space specifies 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 character specifies that zero-padding
should be
used rather than blank-padding. This flag
is ignored if
used with a precision specifier and any of
the d, i, o,
u, or x (X) formats. A `-' overrides a `0'
if both are
used.
Field Width:
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 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 characters 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
diouxXfEgGbcs).
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.
f 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.
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.
gG The argument is printed in style f or in style e
(E) whichever
gives full precision in minimum space.
b Characters from the string argument are printed
with backslash-escape
sequences expanded.
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; however if
the precision
is 0 or missing, 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
actual width.
The printf utility exits 0 on success or 1 on failure.
Convert a hexadecimal value to decimal and print it out:
$ printf "%d" 0x20
Print the decimal representation of the character 'a' (see
ascii(7)):
$ printf "%d"'a
echo(1), printf(3)
The printf utility conforms to IEEE Std 1003.2-1992
(``POSIX.2'').
The printf command appeared in 4.3BSD-Reno.
It is important never to pass a string with user-supplied
data as a format
without using `%s'. An attacker can put format specifiers in the
string to mangle your stack, leading to a possible security
hole.
Always be sure to use the proper secure idiom:
printf "%s" "$STRING"
Since arguments are translated from ASCII to floating-point,
and then
back again, floating-point precision may be lost.
OpenBSD 3.6 November 5, 1993
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