formats(5) Standards, Environments, and Macros formats(5)NAMEformats - file format notation
DESCRIPTION
Utility descriptions use a syntax to describe the data organization
within files—stdin, stdout, stderr, input files, and output files—when
that organization is not otherwise obvious. The syntax is similar to
that used by the printf(3C) function. When used for stdin or input
file descriptions, this syntax describes the format that could have
been used to write the text to be read, not a format that could be used
by the scanf(3C) function to read the input file.
Format
The description of an individual record is as follows:
"<format>", [<arg1>, <arg2>, ..., <argn>]
The format is a character string that contains three types of objects
defined below:
characters Characters that are not escape sequences or
conversion specifications, as described below,
are copied to the output.
escape sequences Represent non-graphic characters.
conversion specificationSpecifies the output format of each argument.
(See below.)
The following characters have the following special meaning in the for‐
mat string:
`` '' (An empty character position.) One or more
blank characters.
/\ Exactly one space character.
The notation for spaces allows some flexibility for application output.
Note that an empty character position in format represents one or more
blank characters on the output (not white space, which can include new‐
line characters). Therefore, another utility that reads that output as
its input must be prepared to parse the data using scanf(3C), awk(1),
and so forth. The character is used when exactly one space character
is output.
Escape Sequences
The following table lists escape sequences and associated actions on
display devices capable of the action.
Sequence Character Terminal Action
\\ backslash None.
\a alert Attempts to alert the user
through audible or visible
notification.
\b backspace Moves the printing position to
one column before the current
position, unless the current
position is the start of a
line.
\f form-feed Moves the printing position to
the initial printing position
of the next logical page.
\n newline Moves the printing position to
the start of the next line.
\r carriage-return Moves the printing position to
the start of the current line.
\t tab Moves the printing position to
the next tab position on the
current line. If there are no
more tab positions left on the
line, the behavior is unde‐
fined.
\v vertical-tab Moves the printing position to
the start of the next vertical
tab position. If there are no
more vertical tab positions
left on the page, the behavior
is undefined.
Conversion Specifications
Each conversion specification is introduced by the percent-sign charac‐
ter (%). After the character %, the following appear in sequence:
flags Zero or more flags, in any order, that modify
the meaning of the conversion specification.
field width An optional string of decimal digits to specify
a minimum field width. For an output field, if
the converted value has fewer bytes than the
field width, it is padded on the left (or
right, if the left-adjustment flag (−),
described below, has been given to the field
width).
precision Gives the minimum number of digits to appear
for the d, o, i, u, x or X conversions (the
field is padded with leading zeros), the number
of digits to appear after the radix character
for the e and f conversions, the maximum number
of significant digits for the g conversion; or
the maximum number of bytes to be written from
a string in s conversion. The precision takes
the form of a period (.) followed by a decimal
digit string; a null digit string is treated as
zero.
conversion characters A conversion character (see below) that indi‐
cates the type of conversion to be applied.
flags
The flags and their meanings are:
− The result of the conversion is left-justified within
the field.
+ The result of a signed conversion always begins with a
sign (+ or −).
<space> If the first character of a signed conversion is not a
sign, a space character is prefixed to the result. This
means that if the space character and + flags both
appear, the space character flag is ignored.
# The value is to be converted to an alternative form.
For c, d, i, u, and s conversions, the behaviour is
undefined. For o conversion, it increases the precision
to force the first digit of the result to be a zero.
For x or X conversion, a non-zero result has 0x or 0X
prefixed to it, respectively. For e, E, f, g, and G
conversions, the result always contains a radix charac‐
ter, even if no digits follow the radix character. For
g and G conversions, trailing zeros are not removed
from the result as they usually are.
0 For d, i, o, u, x, X, e, E, f, g, and G conversions,
leading zeros (following any indication of sign or
base) are used to pad to the field width; no space pad‐
ding is performed. If the 0 and − flags both appear,
the 0 flag is ignored. For d, i, o, u, x and X conver‐
sions, if a precision is specified, the 0 flag is
ignored. For other conversions, the behaviour is unde‐
fined.
Conversion Characters
Each conversion character results in fetching zero or more arguments.
The results are undefined if there are insufficient arguments for the
format. If the format is exhausted while arguments remain, the excess
arguments are ignored.
The conversion characters and their meanings are:
d,i,o,u,x,X The integer argument is written as signed decimal (d or
i), unsigned octal (o), unsigned decimal (u), or
unsigned hexadecimal notation (x and X). The d and i
specifiers convert to signed decimal in the style
[−]dddd. The x conversion uses the numbers and letters
0123456789abcdef and the X conversion uses the numbers
and letters 0123456789ABCDEF. The precision component
of the argument specifies the minimum number of digits
to appear. If the value being converted can be repre‐
sented in fewer digits than the specified minimum, it
is expanded with leading zeros. The default precision
is 1. The result of converting a zero value with a pre‐
cision of 0 is no characters. If both the field width
and precision are omitted, the implementation may pre‐
cede, follow or precede and follow numeric arguments of
types d, i and u with blank characters; arguments of
type o (octal) may be preceded with leading zeros.
The treatment of integers and spaces is different from
the printf(3C) function in that they can be surrounded
with blank characters. This was done so that, given a
format such as:
"%d\n",<foo>
the implementation could use a printf() call such as:
printf("%6d\n", foo);
and still conform. This notation is thus somewhat like
scanf() in addition to printf().
f The floating point number argument is written in deci‐
mal notation in the style [−]ddd.ddd, where the number
of digits after the radix character (shown here as a
decimal point) is equal to the precision specification.
The LC_NUMERIC locale category determines the radix
character to use in this format. If the precision is
omitted from the argument, six digits are written after
the radix character; if the precision is explicitly 0,
no radix character appears.
e,E The floating point number argument is written in the
style [−]d.ddde±dd (the symbol ± indicates either a
plus or minus sign), where there is one digit before
the radix character (shown here as a decimal point) and
the number of digits after it is equal to the preci‐
sion. The LC_NUMERIC locale category determines the
radix character to use in this format. When the preci‐
sion is missing, six digits are written after the
radix character; if the precision is 0, no radix char‐
acter appears. The E conversion character produces a
number with E instead of e introducing the exponent.
The exponent always contains at least two digits. How‐
ever, if the value to be written requires an exponent
greater than two digits, additional exponent digits are
written as necessary.
g,G The floating point number argument is written in style
f or e (or in style E in the case of a G conversion
character), with the precision specifying the number of
significant digits. The style used depends on the value
converted: style g is used only if the exponent result‐
ing from the conversion is less than −4 or greater than
or equal to the precision. Trailing zeros are removed
from the result. A radix character appears only if it
is followed by a digit.
c The integer argument is converted to an unsigned char
and the resulting byte is written.
s The argument is taken to be a string and bytes from the
string are written until the end of the string or the
number of bytes indicated by the precision specifica‐
tion of the argument is reached. If the precision is
omitted from the argument, it is taken to be infinite,
so all bytes up to the end of the string are written.
% Write a % character; no argument is converted.
In no case does a non-existent or insufficient field width cause trun‐
cation of a field; if the result of a conversion is wider than the
field width, the field is simply expanded to contain the conversion
result. The term field width should not be confused with the term pre‐
cision used in the description of %s.
One difference from the C function printf() is that the l and h conver‐
sion characters are not used. There is no differentiation between deci‐
mal values for type int, type long, or type short. The specifications
%d or %i should be interpreted as an arbitrary length sequence of dig‐
its. Also, no distinction is made between single precision and double
precision numbers (float or double in C). These are simply referred to
as floating point numbers.
Many of the output descriptions use the term line, such as:
"%s", <input line>
Since the definition of line includes the trailing newline character
already, there is no need to include a \n in the format; a double new‐
line character would otherwise result.
EXAMPLES
Example 1: To represent the output of a program that prints a date and
time in the form Sunday, July 3, 10:02, where <weekday> and <month> are
strings:
"%s,/\%s/\%d,/\%d:%.2d\n",<weekday>,<month>,<day>,<hour>,<min>
Example 2: To show pi written to 5 decimal places:
"pi/\=/\%.5f\n",<value of pi>
Example 3: To show an input file format consisting of five colon-sepa‐
rated fields:
"%s:%s:%s:%s:%s\n",<arg1>,<arg2>,<arg3>,<arg4>,<arg5>
SEE ALSOawk(1), printf(1), printf(3C), scanf(3C)SunOS 5.10 28 Mar 1995 formats(5)
