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\"      from: @(#)printf.1      8.1 (Berkeley) 6/6/93
\"
Dd November 24, 2024
Dt PRINTF 1
Os
Sh NAME
Nm printf
Nd formatted output
Sh SYNOPSIS
Nm
Op Fl L
Ar format
Op Ar argument ...
Sh DESCRIPTION
Nm
formats and prints its
Ar argument Ns s ,
under control of the
Ar format .
The
Ar 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
Ar argument .
Each
Ar argument
is used only once.
Pp
If the first character of
Ar format
is a dash
Pq Sq Fl ,
Ar format
must (and always may) be preceded by a word consisting of
two dashes
Pq Sq Fl Fl
to prevent it
from being interpreted as an option string.
See
Xr getopt 3 .
Pp
The
Fl L
option causes all floating point values resulting from format
conversions to be printed using
Vt long double
formats, rather than the default
Vt double .
Pp
The
Ar argument Ns s
after the first are treated as strings if the corresponding format is
either
Cm b ,
Cm B ,
Cm c ,
or
Cm s ;
otherwise each is evaluated as a C\~constant, with the following extensions:
Bl -bullet -offset indent
It
A leading plus or minus sign is allowed.
It
If the leading character is a single or double quote,
as part of the
Ar argument
rather than just quoting it for the shell,
the value is the code of the character following that quote character.
No further characters are permitted.
El
Pp
The format string is reused as often as necessary to satisfy the
Ar arguments  .
Any extra format specifications are evaluated with zero or the null
string.
Pp
Character escape sequences are in backslash notation as defined in
St -ansiC .
The characters and their meanings are as follows:
Bl -tag -offset indent -width Cm
It Cm \ea
Write a
Aq bell
character.
It Cm \eb
Write a
Aq backspace
character.
It Cm \ee
Write an
Aq escape
character.
It Cm \ef
Write a
Aq form-feed
character.
It Cm \en
Write a
Aq new-line
character.
It Cm \er
Write a
Aq carriage return
character.
It Cm \et
Write a
Aq tab
character.
It Cm \ev
Write a
Aq vertical tab
character.
It Cm \e\(aq
Write a
Aq single quote
character.
It Cm \e\*q
Write a
Aq double quote
character.
It Cm \e\e
Write a backslash character.
It Cm \e Ns Ar num
Write an 8-bit character whose ASCII
value is the 1-, 2-, or 3-digit octal number
Ar num .
It Cm \ex Ns Ar XX
Write an 8-bit character whose ASCII
value is the 1- or 2-digit hexadecimal number
Ar XX .
El
Pp
Each format specification is introduced by the percent character
Pq Ql \&% .
To produce a literal percent
Pq Ql \&%
in the output, write the percent character twice:
Pq Ql \&%% .
This is not a format conversion,
but a special escape sequence,
and consumes no
Ar argument Ns s .
The remainder of the format specification includes,
in the following order:
Bl -tag -width 5n
It Zero or more of the following unordered flags :
Bl -tag -width Cm
It Cm #
A
Ql \&#
character specifying that the value should be printed in an
Dq alternative form .
For
Cm b ,
Cm c ,
Cm C ,
Cm d ,
and
Cm s
formats, this option has no effect.
For the
Cm o
format the precision of the number is increased to cause the first
character of the numeric output string to be a zero.
For the
Cm x
Pq Cm X
format, a non-zero result has the string
Ql 0x
Pq Ql 0X
prepended to it.
For
Cm e ,
Cm E ,
Cm f ,
Cm F ,
Cm g ,
and
Cm 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
Cm g
and
Cm G
formats, trailing zeros are not removed from the result as they
would otherwise be.
\" I turned this off - decided it isn't a valid use of '#'
\" For the
\" .Cm B
\" format, backslash-escape sequences are expanded first;
It Cm \&\-
A minus sign which specifies
Em left adjustment
of the output in the indicated field;
It Cm \&+
A plus sign which specifies that there should always be
a sign
Po Sq Cm \&+
or
Sq Cm \&\-
Pc
placed before the number when using signed formats;
It Sq Cm \&\ \&
A
Aq space
character which specifies that a space should be left in the
position a minus sign would otherwise appear, before
a non-negative number for a signed format.
A
Ql Cm \&+
overrides a
Aq space
if both are used;
It Cm \&0
A digit zero character which specifies that zero-padding should be used
rather than space-padding to the left of right adjusted fields.
In this case, a sign
Po Sq Cm \&+ ,
Sq Cm \&\-
or
Sq Cm \&\ \&
Pc ,
if included, precedes the padding.
Padding to the right of left adjusted fields always uses spaces.
A
Ql \-
overrides a
Ql \&0
if both are used;
El
Pp
Specifying a flag more than once is not an error, but has no additional effect.
It Field Width :
An optional digit string specifying a
Em field width ;
if the output string has fewer bytes than the field width it will
be 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 a zero appearing after another digit is part of a field width);
It Precision :
An optional period
Pq Ql \&. ,
followed by an optional digit string giving a
Em precision
which specifies the number of digits to appear after the decimal point,
for
Cm e
and
Cm f
formats, or the maximum number of bytes to be printed
from a string
Sm off
Pf ( Cm b ,
Sm on
Cm B ,
and
Cm s
formats); if the digit string is missing, the precision is treated
as zero;
It Format :
A character which indicates the type of format to use (one of
Cm diouxXfFeEgGaAbBcCs ) .
El
Pp
A field width or precision may be
Sq Cm \&*
instead of a digit string.
In this case the next
Ar argument ,
preceding the value to be converted,
supplies the field width or precision.
It must be an unsigned integer constant.
If both the field width and precision are
Sq Cm \&*
then two
Ar argument Ns s
are required, with the field width preceding the precision,
and the value to be converted following those.
Pp
The format characters and their meanings are:
Bl -tag -width Fl
It Cm diouXx
The
Ar argument ,
which must represent an integer constant,
with an optional leading plus or minus sign,
is printed as a signed decimal
Cm ( d
or
Cm i ) ,
unsigned octal
Cm ( o ) ,
unsigned decimal
Cm ( u ) ,
or unsigned hexadecimal
Cm ( X
or
Cm x ) .
It Cm fF
The
Ar argument
is printed in the style
Oo Li \&\- Oc Ns Ar \&\^ddd Ns Li \&\^\&. Ns Ar ddd
where the number of
Ar d Ns \|'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.
If the number is Infinity, or Not-a-Number, then
Ql inf
or
Ql nan
is printed for
Cm f
format, and
Ql INF
or
Ql NAN
for
Cm F
format.
It Cm eE
The
Ar argument
is printed in the style
Oo Li \&\- Oc Ns Ar \&\^d Ns Li \&. Ns Ar ddd Ns Li \&\|e\*(Pm Ns Ar \&\|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
Ql E
is used for an
Cm E
format, and upper-case for Infinity and NaN as for
Cm F
format.
It Cm gG
The
Ar argument
is printed in style
Cm f
Pq Cm F
or in style
Cm e
Pq Cm E
whichever gives full precision in minimum space.
It Cm aA
The
Ar argument
is treated as a floating point number,
for which the underlying hexadecimal representation is
printed.
See
Xr printf 3
for the details.
It Cm b
Characters from the string
Ar argument
are printed with backslash-escape sequences expanded.
Pp
The following additional backslash-escape sequences are supported:
Bl -tag -width Cm
It Cm \ec
Causes
Nm
to ignore any remaining characters in the string operand containing it,
any remaining operands, and any additional characters in
the format operand.
It Cm \e0 Ns Ar num
Write an 8-bit character whose ASCII value is the 1-, 2-, or
3-digit octal number
Ar num .
It Cm \e^ Ns Ar c
Write the control character
Ar c .
Generates characters
Sq \e000
through
Sq \e037 ,
and
Sq \e177
(from
Ql \e^\&? ) .
It Cm \eM^ Ns Ar c
Write the control character
Ar c
with the 8th bit set.
Generates characters
Sq \e200
through
Sq \e237 ,
and
Sq \e377
(from
Ql \eM^\&? ) .
It Cm \eM\- Ns Ar c
Write the character
Ar c
with the 8th bit set.
Generates characters
Sq \e240
through
Sq \e376 .
El
It Cm B
Characters from the string
Ar argument
are printed with unprintable characters backslash-escaped using the
Sq Cm \e Ns Ar c ,
Sq Cm \e^ Ns Ar c ,
Sq Cm \eM^ Ns Ar c ,
or
Sq Cm \eM\- Ns Ar c
formats described above.
It Cm c
The first character of the next
Ar argument
is printed.
It Cm C
The
Ar argument ,
which must represent an integer constant,
with an optional leading plus or minus sign,
is treated as a wide character code point, and printed.
It Cm s
Characters from the string
Ar argument
are printed until the end is reached or until the number of bytes
indicated by the precision specification is reached; if the
precision is omitted, all characters in the string are printed.
El
Pp
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.
Pp
If an argument required by a format string is present, but is not in
a format expected by the format string conversion, a warning will be
printed to standard error, identifying the argument by number
Pq 1 is the first after the format string
and usually also by content.
In such a case a value will still be produced, and printed,
and processing will continue, but
Nm
will eventually exit with a failure status.
Sh EXIT STATUS
Ex -std
Sh SEE ALSO
Xr echo 1 ,
Xr printf 3 ,
Xr vis 3 ,
Xr printf 9
Sh STANDARDS
The
Nm
utility conforms to
St -p1003.1-2001 .
Pp
Support for the floating point formats and
Sq Cm \&*
as a field width and precision
are optional in POSIX.
Pp
The behaviour of the
Cm \&%B
and
Cm \&%C
formats and the
Cm \e\(aq ,
Cm \e\*q ,
Cm \ee ,
Cm \ex Ns Ar XX ,
and
Cm \e Ns Oo Cm M Oc Ns Oo Cm \- Ns Li \&\(or Ns Cm ^ Oc Ns Ar c
escape sequences are undefined in POSIX.
Sh BUGS
Since the floating point numbers are translated from ASCII to
floating-point and then back again, floating-point precision may be lost.
Pp
Hexadecimal character constants given as escapes in strings are
restricted to, and should be specified as, two hexadecimal characters.
This is contrary to the ISO C standard but
does guarantee detection of the end of the constant.
Sh NOTES
All formats which treat the
Ar argument
as a number first convert the
Ar argument
from its external representation as a character string
to an internal numeric representation, and then apply the
format to the internal numeric representation, producing
another external character string representation.
One might expect the
Cm \&%c
format to do likewise, but in fact it does not.
Pp
To convert a string representation of a decimal, octal, or hexadecimal
number into the corresponding character,
using a portable invocation,
two nested
Nm
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 format.
For example, the following command outputs the character whose code
is 0x0a, which is a newline in ASCII:
Pp
Dl printf \*q$(printf \(aq\e\e%o\(aq 0x0a)\*q
Pp
In this implementation of
Nm
it is possible to achieve the same result using one invocation:
Pp
Dl printf %C 0x0a

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