'\" et

.TH PRINTF "1P" 2013 "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\(hy2008,

.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\(hy2008,

.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\(hy2008,

.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 may 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\(hy2008,

.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

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 argument

operands. Any extra

.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 minus-sign 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 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 is not considered an error if an argument operand is not completely

used for a

.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\(hy2008 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\(hy2008 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

\fB

printf "\eaPlease fill in the following: \enName: "

read name

printf "Phone number: "

read phone

.fi \fR

.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

\fB

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 \fR

.P

.RE

The command:

.sp

.RS 4

.nf

\fB

printf "%5d%4d\en" 1 21 321 4321 54321

.fi \fR

.P

.RE

.P

produces:

.sp

.RS 4

.nf

\fB

    1  21

  3214321

54321   0

.fi \fR

.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

\(mi9999999999@\(mi2147483648@printf: "\(mi9999999999" 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\(hy2008. 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

\fB

printf "%d\en" 3 +3 \(mi3 \e'3 \e"+3 "'\(mi3"

.fi \fR

.P

.RE

.P

produces:

.IP 3 6

Numeric value of constant 3

.IP 3 6

Numeric value of constant 3

.IP "\(mi3" 6

Numeric value of constant \(mi3

.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 '\(mi' 

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\(hy2008.

.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\(hy2008,

.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\(hy2008,

.IR "Chapter 5" ", " "File Format Notation",

.IR "Chapter 8" ", " "Environment Variables"

.P

The System Interfaces volume of POSIX.1\(hy2008,

.IR "\fIfprintf\fR\^(\|)",

.IR "\fIstrtod\fR\^(\|)"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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 .