path: root/usr/src/man/man7/formats.7

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.\"
.TH FORMATS 7 "Mar 28, 1995"
.SH NAME
formats \- file format notation
.SH DESCRIPTION
.sp
.LP
Utility descriptions use a syntax to describe the data organization within
files\(emstdin, stdout, stderr, input files, and output files\(emwhen that
organization is not otherwise obvious. The syntax is similar to that used by
the  \fBprintf\fR(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
\fBscanf\fR(3C) function to read the input file.
.SS "Format"
.sp
.LP
The description of an individual record is as follows:
.sp
.in +2
.nf
"<\fBformat\fR>", [<\fIarg1\fR>, <\fIarg2\fR>, .\|.\|., <\fIargn\fR>]
.fi
.in -2

.sp
.LP
The \fBformat\fR is a character string that contains three types of objects
defined below:
.sp
.ne 2
.na
\fB\fI\fR\fIcharacters\fR\fI\fR \fR
.ad
.RS 30n
Characters that are not \fIescape sequences\fR or \fIconversion
specifications\fR, as described below, are copied to the output.
.RE

.sp
.ne 2
.na
\fB\fI\fR\fIescape sequences\fR\fI\fR \fR
.ad
.RS 30n
Represent non-graphic characters.
.RE

.sp
.ne 2
.na
\fB\fI\fR\fIconversion specifications\fR\fI\fR \fR
.ad
.RS 30n
Specifies the output format of each argument. (See below.)
.RE

.sp
.LP
The following characters have the following special meaning in the format
string:
.sp
.ne 2
.na
\fB`` \&''\fR
.ad
.RS 11n
(An empty character position.) One or more blank characters.
.RE

.sp
.ne 2
.na
\fB/\e \fR
.ad
.RS 11n
Exactly one space character.
.RE

.sp
.LP
The notation for spaces allows some flexibility for application output. Note
that an empty character position in \fBformat\fR represents one or more blank
characters on the output (not \fIwhite space\fR, which can include newline
characters). Therefore, another utility that reads that output as its input
must be prepared to parse the data using \fBscanf\fR(3C), \fBawk\fR(1), and so
forth. The  character is used when exactly one space character is output.
.SS "Escape Sequences"
.sp
.LP
The following table lists escape sequences and  associated actions on display
devices capable of the action.
.sp

.sp
.TS
c c c
l l l .
\fBSequence\fR	\fBCharacter\fR	\fBTerminal Action\fR
_
\fB\e\e\fR	backslash	None.
\fB\ea\fR	alert	T{
Attempts to alert the user through audible or visible notification.
T}
\fB\eb\fR	backspace	T{
Moves the printing position to one column before the current position, unless the current position is the start of a line.
T}
\fB\ef\fR	form-feed	T{
Moves the printing position to the initial printing position of the next logical page.
T}
\fB\en\fR	newline	T{
Moves the printing position to the start of the next line.
T}
\fB\er\fR	carriage-return	T{
Moves the printing position to the start of the current line.
T}
\fB\et\fR	tab	T{
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 undefined.
T}
\fB\ev\fR	vertical-tab	T{
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.
T}
.TE

.SS "Conversion Specifications"
.sp
.LP
Each conversion specification is introduced by the percent-sign character (%).
After the character %, the following appear in sequence:
.sp
.ne 2
.na
\fB\fI\fR\fIflags\fR\fI\fR \fR
.ad
.RS 26n
Zero or more \fIflags\fR, in any order, that modify the meaning of the
conversion specification.
.RE

.sp
.ne 2
.na
\fB\fI\fR\fIfield width\fR\fI\fR \fR
.ad
.RS 26n
An optional string of decimal digits to specify a minimum \fIfield width\fR.
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 (\(mi),
described below, has been given to the field width).
.RE

.sp
.ne 2
.na
\fB\fI\fR\fIprecision\fR\fI\fR \fR
.ad
.RS 26n
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.
.RE

.sp
.ne 2
.na
\fB\fI\fR\fIconversion characters\fR\fI\fR \fR
.ad
.RS 26n
A conversion character (see below) that indicates the type of conversion to be
applied.
.RE

.SS "\fIflags\fR"
.sp
.LP
The \fIflags\fR and their meanings are:
.sp
.ne 2
.na
\fB\fI\(mi\fR \fR
.ad
.RS 12n
The result of the conversion is left-justified within the field.
.RE

.sp
.ne 2
.na
\fB\fI+\fR \fR
.ad
.RS 12n
The result of a signed conversion always begins with a sign (+ or \(mi).
.RE

.sp
.ne 2
.na
\fB\fI<space>\fR \fR
.ad
.RS 12n
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.
.RE

.sp
.ne 2
.na
\fB\fI#\fR \fR
.ad
.RS 12n
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 character, 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.
.RE

.sp
.ne 2
.na
\fB\fI0\fR \fR
.ad
.RS 12n
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
padding is performed. If the 0 and \(mi flags both appear, the 0 flag is
ignored. For d, i, o, u, x and X conversions, if a precision is specified, the
0 flag is ignored. For other conversions, the behaviour is undefined.
.RE

.SS "Conversion Characters"
.sp
.LP
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.
.sp
.LP
The \fIconversion characters\fR and their meanings are:
.sp
.ne 2
.na
\fB\fId,i,o,u,x,X\fR \fR
.ad
.RS 16n
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 \fB[\fR\(mi\fB]\fR\fIdddd\fR.
The x conversion uses the numbers and letters 0123456789abcdef and the X
conversion uses the numbers and letters 0123456789ABCDEF. The \fIprecision\fR
component of the argument specifies the minimum number of digits to appear. If
the value being converted can be represented 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 precision of 0 is no characters. If
both the field width and precision are omitted, the implementation may precede,
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.
.sp
The treatment of integers and spaces is different from the \fBprintf\fR(3C)
function in that they can be surrounded with blank characters. This was done so
that, given a format such as:
.sp
.in +2
.nf
"%d\en",<\fIfoo\fR>
.fi
.in -2

the implementation could use a \fBprintf()\fR call such as:
.sp
.in +2
.nf
printf("%6d\en", \fIfoo\fR);
.fi
.in -2

and still conform. This notation is thus somewhat like \fBscanf()\fR in
addition to \fBprintf(\|).\fR
.RE

.sp
.ne 2
.na
\fB\fIf\fR \fR
.ad
.RS 16n
The floating point number argument is written in decimal notation in the style
\fB[\fR\(mi\fB]\fR\fIddd\fR.\fIddd\fR, where the number of digits after the
radix character (shown here as a decimal point) is equal to the \fIprecision\fR
specification. The \fBLC_NUMERIC\fR locale category determines the radix
character to use in this format. If the \fIprecision\fR is omitted from the
argument, six digits are written after the radix character; if the
\fIprecision\fR is explicitly 0, no radix character appears.
.RE

.sp
.ne 2
.na
\fB\fIe,E\fR \fR
.ad
.RS 16n
The floating point number argument is written in the style
\fB[\fR\(mi\fB]\fR\fId\fR.\fIddd\fRe\(+-\fBdd\fR (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 precision. The  \fBLC_NUMERIC\fR locale category determines the
radix character to use in this format. When the precision is missing, six
digits are  written after the radix character; if the precision is 0, no radix
character appears. The E conversion character produces a number with E instead
of e introducing the exponent. The exponent always contains at least two
digits. However, if the value to be written requires an exponent greater than
two digits, additional exponent digits are written as necessary.
.RE

.sp
.ne 2
.na
\fB\fIg,G\fR \fR
.ad
.RS 16n
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 resulting from the conversion is less than \(mi4
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.
.RE

.sp
.ne 2
.na
\fB\fIc\fR \fR
.ad
.RS 16n
The integer argument is converted to an \fBunsigned char\fR and the resulting
byte is written.
.RE

.sp
.ne 2
.na
\fB\fIs\fR \fR
.ad
.RS 16n
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
\fIprecision\fR specification 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.
.RE

.sp
.ne 2
.na
\fB\fI%\fR \fR
.ad
.RS 16n
Write a % character; no argument is converted.
.RE

.sp
.LP
In no case does a non-existent or insufficient \fIfield width\fR cause
truncation 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
\fIfield width\fR should not be confused with the term \fIprecision\fR used in
the description of %s.
.sp
.LP
One difference from the C function \fBprintf()\fR is that the l and h
conversion characters are not used. There is no differentiation between decimal
values for type \fBint\fR, type  \fBlong\fR, or type  \fBshort\fR. The
specifications %d or %i should be interpreted as an arbitrary length sequence
of digits. Also, no distinction is made between single precision and double
precision numbers (\fBfloat\fR or \fBdouble\fR in C).  These are simply
referred to as floating point numbers.
.sp
.LP
Many of the output descriptions  use the term \fBline\fR, such as:
.sp
.in +2
.nf
"%s", <\fIinput line\fR>
.fi
.in -2

.sp
.LP
Since the definition of \fBline\fR includes the trailing newline character
already, there is no need to include a \fB\en\fR in the format; a double
newline character would otherwise result.
.SH EXAMPLES
.LP
\fBExample 1 \fRTo represent the output of a program that prints a date and
time in the form Sunday, July 3, 10:02, where \fI<weekday>\fR and \fI<month>\fR
are strings:
.sp
.in +2
.nf
"%s,/\e%s/\e%d,/\e%d:%.2d\en",<\fIweekday\fR>,<\fImonth\fR>,<\fIday\fR>,<\fIhour\fR>,<\fImin\fR>
.fi
.in -2

.LP
\fBExample 2 \fRTo show pi written to 5 decimal places:
.sp
.in +2
.nf
"pi/\e=/\e%.5f\en",<\fIvalue of pi\fR>
.fi
.in -2

.LP
\fBExample 3 \fRTo show an input file format consisting of five colon-separated
fields:
.sp
.in +2
.nf
"%s:%s:%s:%s:%s\en",<\fIarg1\fR>,<\fIarg2\fR>,<\fIarg3\fR>,<\fIarg4\fR>,<\fIarg5\fR>
.fi
.in -2

.SH SEE ALSO
.sp
.LP
.BR awk (1),
.BR printf (1),
.BR printf (3C),
.BR scanf (3C)