'\" et
.TH PRINTF "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
printf
\(em write formatted output
.SH SYNOPSIS
.LP
.nf
printf \fIformat\fB [\fIargument\fR...\fB]\fR
.fi
.SH DESCRIPTION
The
.IR printf
utility shall write formatted operands to the standard output. The
.IR argument
operands shall be formatted under control of the
.IR format
operand.
.SH OPTIONS
None.
.SH OPERANDS
The following operands shall be supported:
.IP "\fIformat\fR" 10
A string describing the format to use to write the remaining operands.
See the EXTENDED DESCRIPTION section.
.IP "\fIargument\fR" 10
The strings to be written to standard output, under the control of
.IR format .
See the EXTENDED DESCRIPTION section.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR printf :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
the precedence of internationalization variables used to determine the
values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
.IP "\fILC_NUMERIC\fP" 10
.br
Determine the locale for numeric formatting. It shall affect the
format of numbers written using the
.BR e ,
.BR E ,
.BR f ,
.BR g ,
and
.BR G
conversion specifier characters (if supported).
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
See the EXTENDED DESCRIPTION section.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
The
.IR format
operand shall be used as the
.IR format
string described in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 5" ", " "File Format Notation"
with the following exceptions:
.IP " 1." 4
A
<space>
in the format string, in any context other than a flag of a conversion
specification, shall be treated as an ordinary character that is copied
to the output.
.IP " 2." 4
A
.BR ' ' 
character in the format string shall be treated as a
.BR ' ' 
character, not as a
<space>.
.IP " 3." 4
In addition to the escape sequences shown in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 5" ", " "File Format Notation"
(\c
.BR '\e\e' ,
.BR '\ea' ,
.BR '\eb' ,
.BR '\ef' ,
.BR '\en' ,
.BR '\er' ,
.BR '\et' ,
.BR '\ev' ),
.BR \(dq\eddd\(dq ,
where
.IR ddd
is a one, two, or three-digit octal number, shall be written as a byte
with the numeric value specified by the octal number.
.IP " 4." 4
The implementation shall not precede or follow output from the
.BR d
or
.BR u
conversion specifiers with
<blank>
characters not specified by the
.IR format
operand.
.IP " 5." 4
The implementation shall not precede output from the
.BR o
conversion specifier with zeros not specified by the
.IR format
operand.
.IP " 6." 4
The
.BR a ,
.BR A ,
.BR e ,
.BR E ,
.BR f ,
.BR F ,
.BR g ,
and
.BR G
conversion specifiers need not be supported.
.IP " 7." 4
An additional conversion specifier character,
.BR b ,
shall be supported as follows. The argument shall be taken to be a
string that can contain
<backslash>-escape
sequences. The following
<backslash>-escape
sequences shall be supported:
.RS 4 
.IP -- 4
The escape sequences listed in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 5" ", " "File Format Notation"
(\c
.BR '\e\e' ,
.BR '\ea' ,
.BR '\eb' ,
.BR '\ef' ,
.BR '\en' ,
.BR '\er' ,
.BR '\et' ,
.BR '\ev' ),
which shall be converted to the characters they represent
.IP -- 4
.BR \(dq\e0ddd\(dq ,
where
.IR ddd
is a zero, one, two, or three-digit octal number that shall be
converted to a byte with the numeric value specified by the octal
number
.IP -- 4
.BR '\ec' ,
which shall not be written and shall cause
.IR printf
to ignore any remaining characters in the string operand containing it,
any remaining string operands, and any additional characters in the
.IR format
operand
.P
The interpretation of a
<backslash>
followed by any other sequence of characters is unspecified.
.P
Bytes from the converted string shall be written until the end of the
string or the number of bytes indicated by the precision specification
is reached. If the precision is omitted, it shall be taken to be
infinite, so all bytes up to the end of the converted string shall be
written.
.RE
.IP " 8." 4
For each conversion specification that consumes an argument, the next
.IR argument
operand shall be evaluated and converted to the appropriate
type for the conversion as specified below.
.IP " 9." 4
The
.IR format
operand shall be reused as often as necessary to satisfy the
.IR argument
operands. Any extra
.BR b ,
.BR c ,
or
.BR s
conversion specifiers shall be evaluated as if a null string
argument were supplied; other extra conversion specifications shall be
evaluated as if a zero argument were supplied. If the
.IR format
operand contains no conversion specifications and
.IR argument
operands are present, the results are unspecified.
.IP 10. 4
If a character sequence in the
.IR format
operand begins with a
.BR '%' 
character, but does not form a valid conversion specification, the
behavior is unspecified.
.IP 11. 4
The argument to the
.BR c
conversion specifier can be a string containing zero or more bytes. If
it contains one or more bytes, the first byte shall be written and any
additional bytes shall be ignored. If the argument is an empty string,
it is unspecified whether nothing is written or a null byte is written.
.P
The
.IR argument
operands shall be treated as strings if the corresponding conversion
specifier is
.BR b ,
.BR c ,
or
.BR s ,
and shall be evaluated as if by the
\fIstrtod\fR()
function if the corresponding conversion specifier is
.BR a ,
.BR A ,
.BR e ,
.BR E ,
.BR f ,
.BR F ,
.BR g ,
or
.BR G .
Otherwise, they shall be evaluated as unsuffixed C integer constants,
as described by the ISO\ C standard, with the following extensions:
.IP " *" 4
A leading
<plus-sign>
or
<hyphen-minus>
shall be allowed.
.IP " *" 4
If the leading character is a single-quote or double-quote, the value
shall be the numeric value in the underlying codeset of the character
following the single-quote or double-quote.
.IP " *" 4
Suffixed integer constants may be allowed.
.P
If an
.IR argument
operand cannot be completely converted into an internal
value appropriate to the corresponding conversion specification, a
diagnostic message shall be written to standard error and the utility
shall not exit with a zero exit status, but shall continue processing
any remaining operands and shall write the value accumulated at the
time the error was detected to standard output.
.P
It shall not be considered an error if an
.IR argument
operand is not completely used for a
.BR b ,
.BR c ,
or
.BR s
conversion.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
Successful completion.
.IP >0 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
The floating-point formatting conversion specifications of
\fIprintf\fR()
are not required because all arithmetic in the shell is integer
arithmetic. The
.IR awk
utility performs floating-point calculations and provides its own
.BR printf
function. The
.IR bc
utility can perform arbitrary-precision floating-point arithmetic, but
does not provide extensive formatting capabilities. (This
.IR printf
utility cannot really be used to format
.IR bc
output; it does not support arbitrary precision.) Implementations are
encouraged to support the floating-point conversions as an extension.
.P
Note that this
.IR printf
utility, like the
\fIprintf\fR()
function defined in the System Interfaces volume of POSIX.1\(hy2017 on which it is based, makes no special
provision for dealing with multi-byte characters when using the
.BR %c
conversion specification or when a precision is specified in a
.BR %b
or
.BR %s
conversion specification. Applications should be extremely cautious
using either of these features when there are multi-byte characters in
the character set.
.P
No provision is made in this volume of POSIX.1\(hy2017 which allows field widths and precisions
to be specified as
.BR '*' 
since the
.BR '*' 
can be replaced directly in the
.IR format
operand using shell variable substitution. Implementations can also
provide this feature as an extension if they so choose.
.P
Hexadecimal character constants as defined in the ISO\ C standard are not
recognized in the
.IR format
operand because there is no consistent way to detect the end of the
constant. Octal character constants are limited to, at most, three
octal digits, but hexadecimal character constants are only terminated
by a non-hex-digit character. In the ISO\ C standard, the
.BR \(dq##\(dq 
concatenation operator can be used to terminate a constant and follow
it with a hexadecimal character to be written. In the shell,
concatenation occurs before the
.IR printf
utility has a chance to parse the end of the hexadecimal constant.
.P
The
.BR %b
conversion specification is not part of the ISO\ C standard; it has been added
here as a portable way to process
<backslash>-escapes
expanded in string operands as provided by the
.IR echo
utility. See also the APPLICATION USAGE section of
.IR "\fIecho\fR\^"
for ways to use
.IR printf
as a replacement for all of the traditional versions of the
.IR echo
utility.
.P
If an argument cannot be parsed correctly for the corresponding
conversion specification, the
.IR printf
utility is required to report an error. Thus, overflow and extraneous
characters at the end of an argument being used for a numeric
conversion shall be reported as errors.
.SH EXAMPLES
To alert the user and then print and read a series of prompts:
.sp
.RS 4
.nf

printf "\eaPlease fill in the following: \enName: "
read name
printf "Phone number: "
read phone
.fi
.P
.RE
.P
To read out a list of right and wrong answers from a file, calculate
the percentage correctly, and print them out. The numbers are
right-justified and separated by a single
<tab>.
The percentage is written to one decimal place of accuracy:
.sp
.RS 4
.nf

while read right wrong ; do
    percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
    printf "%2d right\et%2d wrong\et(%s%%)\en" \e
        $right $wrong $percent
done < database_file
.fi
.P
.RE
The command:
.sp
.RS 4
.nf

printf "%5d%4d\en" 1 21 321 4321 54321
.fi
.P
.RE
.P
produces:
.sp
.RS 4
.nf

    1  21
  3214321
54321   0
.fi
.P
.RE
.P
Note that the
.IR format
operand is used three times to print all of the given strings and that
a
.BR '0' 
was supplied by
.IR printf
to satisfy the last
.BR %4d
conversion specification.
.P
The
.IR printf
utility is required to notify the user when conversion errors are
detected while producing numeric output; thus, the following results
would be expected on an implementation with 32-bit twos-complement
integers when
.BR %d
is specified as the
.IR format
operand:
.br
.TS
center tab(@) box;
cB | cB | cB
cB | cB | cB
lf5 | lf5 | lf7.
@Standard
Argument@Output@Diagnostic Output
_
5a@5@printf: "5a" not completely converted
9999999999@2147483647@printf: "9999999999" arithmetic overflow
\-9999999999@\-2147483648@printf: "\-9999999999" arithmetic overflow
ABC@0@printf: "ABC" expected numeric value
.TE
.P
The diagnostic message format is not specified, but these examples
convey the type of information that should be reported. Note that the
value shown on standard output is what would be expected as the return
value from the
\fIstrtol\fR()
function as defined in the System Interfaces volume of POSIX.1\(hy2017. A similar correspondence exists
between
.BR %u
and
\fIstrtoul\fR()
and
.BR %e ,
.BR %f ,
and
.BR %g
(if the implementation supports floating-point conversions) and
\fIstrtod\fR().
.P
In a locale using the ISO/IEC\ 646:\|1991 standard as the underlying codeset, the command:
.sp
.RS 4
.nf

printf "%d\en" 3 +3 -3 \e\(aq3 \e"+3 "\(aq-3"
.fi
.P
.RE
.P
produces:
.IP 3 6
Numeric value of constant 3
.IP 3 6
Numeric value of constant 3
.IP "\-3" 6
Numeric value of constant \-3
.IP 51 6
Numeric value of the character
.BR '3' 
in the ISO/IEC\ 646:\|1991 standard codeset
.IP 43 6
Numeric value of the character
.BR '\(pl' 
in the ISO/IEC\ 646:\|1991 standard codeset
.IP 45 6
Numeric value of the character
.BR '\-' 
in the ISO/IEC\ 646:\|1991 standard codeset
.P
Note that in a locale with multi-byte characters, the value of a
character is intended to be the value of the equivalent of the
.BR wchar_t
representation of the character as described in the System Interfaces volume of POSIX.1\(hy2017.
.SH RATIONALE
The
.IR printf
utility was added to provide functionality that has historically been
provided by
.IR echo .
However, due to irreconcilable differences in the various versions of
.IR echo
extant, the version has few special features, leaving those to this new
.IR printf
utility, which is based on one in the Ninth Edition system.
.P
The EXTENDED DESCRIPTION section almost exactly matches the
\fIprintf\fR()
function in the ISO\ C standard, although it is described in terms of the file
format notation in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 5" ", " "File Format Notation".
.P
Earlier versions of this standard specified that arguments for all
conversions other than
.BR b ,
.BR c ,
and
.BR s
were evaluated in the same way (as C constants, but with stated
exceptions). For implementations supporting the floating-point conversions
it was not clear whether integer conversions need only accept integer
constants and floating-point conversions need only accept floating-point
constants, or whether both types of conversions should accept both
types of constants. Also by not distinguishing between them, the
requirement relating to a leading single-quote or double-quote applied
to floating-point conversions even though this provided no useful
functionality to applications that was not already available through
the integer conversions. The current standard clarifies the situation
by specifying that the arguments for floating-point conversions are
evaluated as if by
\fIstrtod\fR(),
and the arguments for integer conversions are evaluated as C integer
constants, with the special treatment of leading single-quote and
double-quote applying only to integer conversions.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIawk\fR\^",
.IR "\fIbc\fR\^",
.IR "\fIecho\fR\^"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 5" ", " "File Format Notation",
.IR "Chapter 8" ", " "Environment Variables"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIfprintf\fR\^(\|)",
.IR "\fIstrtod\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .