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printf(P) printf(P)
NAME
printf - write formatted output
SYNOPSIS
printf format[argument...]
DESCRIPTION
The printf utility shall write formatted operands to the
standard output. The argument operands shall be format-
ted under control of the format operand.
OPTIONS
None.
OPERANDS
The following operands shall be supported:
format A string describing the format to use to write
the remaining operands. See the EXTENDED
DESCRIPTION section.
argument
The strings to be written to standard output,
under the control of format. See the EXTENDED
DESCRIPTION section.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the
execution of printf:
LANG Provide a default value for the internationaliza-
tion variables that are unset or null. (See the
Base Definitions volume of IEEE Std 1003.1-2001,
Section 8.2, Internationalization Variables for
the precedence of internationalization variables
used to determine the values of locale cate-
gories.)
LC_ALL If set to a non-empty string value, override the
values of all the other internationalization
variables.
LC_CTYPE
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).
LC_MESSAGES
Determine the locale that should be used to
affect the format and contents of diagnostic mes-
sages written to standard error.
LC_NUMERIC
Determine the locale for numeric formatting. It
shall affect the format of numbers written using
the e , E , f , g , and G conversion specifier
characters (if supported).
NLSPATH
Determine the location of message catalogs for
the processing of LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
See the EXTENDED DESCRIPTION section.
STDERR
The standard error shall be used only for diagnostic
messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
The format operand shall be used as the format string
described in the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 5, File Format Notation
with the following exceptions:
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.
A '' character in the format string shall be treated as
a '' character, not as a <space>.
In addition to the escape sequences shown in the Base
Definitions volume of IEEE Std 1003.1-2001, Chapter 5,
File Format Notation ( '\\' , '\a' , '\b' , '\f' , '\n'
, '\r' , '\t' , '\v' ), "\ddd" , where ddd is a one,
two, or three-digit octal number, shall be written as a
byte with the numeric value specified by the octal num-
ber.
The implementation shall not precede or follow output
from the d or u conversion specifiers with <blank>s not
specified by the format operand.
The implementation shall not precede output from the o
conversion specifier with zeros not specified by the
format operand.
The e , E , f , g , and G conversion specifiers need not
be supported.
An additional conversion specifier character, 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 sup-
ported:
The escape sequences listed in the Base Defini-
tions volume of IEEE Std 1003.1-2001, Chapter 5,
File Format Notation ( '\\' , '\a' , '\b' , '\f'
, '\n' , '\r' , '\t' , '\v' ), which shall be
converted to the characters they represent
"\0ddd" , where 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
'\c' , which shall not be written and shall cause
printf to ignore any remaining characters in the
string operand containing it, any remaining
string operands, and any additional characters in
the format operand
The interpretation of a backslash followed by any other
sequence of characters is unspecified.
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 preci-
sion is omitted, it shall be taken to be infinite, so
all bytes up to the end of the converted string shall be
written.
For each conversion specification that consumes an argu-
ment, the next argument operand shall be evaluated and
converted to the appropriate type for the conversion as
specified below.
The format operand shall be reused as often as necessary
to satisfy the argument operands. Any extra c or s con-
version 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 format operand contains no con-
version specifications and argument operands are
present, the results are unspecified.
If a character sequence in the format operand begins
with a '%' character, but does not form a valid conver-
sion specification, the behavior is unspecified.
The argument operands shall be treated as strings if the
corresponding conversion specifier is b , c , or s ;
otherwise, it shall be evaluated as a C constant, as
described by the ISO C standard, with the following
extensions:
A leading plus or minus sign shall be allowed.
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.
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 accumu-
lated at the time the error was detected to standard
output.
It is not considered an error if an argument operand is
not completely used for a c or s conversion or if a
string operand's first or second character is used to
get the numeric value of a character.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The floating-point formatting conversion specifications
of printf() are not required because all arithmetic in
the shell is integer arithmetic. The awk utility per-
forms floating-point calculations and provides its own
printf function. The bc utility can perform arbitrary-
precision floating-point arithmetic, but does not pro-
vide extensive formatting capabilities. (This printf
utility cannot really be used to format bc output; it
does not support arbitrary precision.) Implementations
are encouraged to support the floating-point conversions
as an extension.
Note that this printf utility, like the printf() func-
tion defined in the System Interfaces volume of
IEEE Std 1003.1-2001 on which it is based, makes no spe-
cial provision for dealing with multi-byte characters
when using the %c conversion specification or when a
precision is specified in a %b or %s conversion specifi-
cation. Applications should be extremely cautious using
either of these features when there are multi-byte char-
acters in the character set.
No provision is made in this volume of
IEEE Std 1003.1-2001 which allows field widths and pre-
cisions to be specified as '*' since the '*' can be
replaced directly in the format operand using shell
variable substitution. Implementations can also provide
this feature as an extension if they so choose.
Hexadecimal character constants as defined in the ISO C
standard are not recognized in the 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 charac-
ter. In the ISO C standard, the "##" concatenation oper-
ator can be used to terminate a constant and follow it
with a hexadecimal character to be written. In the
shell, concatenation occurs before the printf utility
has a chance to parse the end of the hexadecimal con-
stant.
The %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 echo utility. See also the APPLICATION
USAGE section of echo for ways to use printf as a
replacement for all of the traditional versions of the
echo utility.
If an argument cannot be parsed correctly for the corre-
sponding conversion specification, the printf utility is
required to report an error. Thus, overflow and extrane-
ous characters at the end of an argument being used for
a numeric conversion shall be reported as errors.
EXAMPLES
To alert the user and then print and read a series of
prompts:
printf "\aPlease fill in the following: \nName: "
read name
printf "Phone number: "
read phone
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:
while read right wrong ; do
percent=$(echo "scale=1;($right*100)/($right+$wrong)" | bc)
printf "%2d right\t%2d wrong\t(%s%%)\n" \
$right $wrong $percent
done < database_file
The command:
printf "%5d%4d\n" 1 21 321 4321 54321
produces:
1 21
3214321
54321 0
Note that the format operand is used three times to
print all of the given strings and that a '0' was sup-
plied by printf to satisfy the last %4d conversion spec-
ification.
The 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 %d is specified as the format operand:
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
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 stan-
dard output is what would be expected as the return
value from the strtol() function as defined in the Sys-
tem Interfaces volume of IEEE Std 1003.1-2001. A similar
correspondence exists between %u and strtoul() and %e ,
%f , and %g (if the implementation supports floating-
point conversions) and strtod().
In a locale using the ISO/IEC 646:1991 standard as the
underlying codeset, the command:
printf "%d\n" 3 +3 -3 \'3 \"+3 "'-3"
produces:
3 Numeric value of constant 3
3 Numeric value of constant 3
-3 Numeric value of constant -3
51 Numeric value of the character '3' in the
ISO/IEC 646:1991 standard codeset
43 Numeric value of the character '+' in the
ISO/IEC 646:1991 standard codeset
45 Numeric value of the character '-' in the
ISO/IEC 646:1991 standard codeset
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 wchar_t representation of the charac-
ter as described in the System Interfaces volume of
IEEE Std 1003.1-2001.
RATIONALE
The printf utility was added to provide functionality
that has historically been provided by echo. However,
due to irreconcilable differences in the various ver-
sions of echo extant, the version has few special fea-
tures, leaving those to this new printf utility, which
is based on one in the Ninth Edition system.
The EXTENDED DESCRIPTION section almost exactly matches
the printf() function in the ISO C standard, although it
is described in terms of the file format notation in the
Base Definitions volume of IEEE Std 1003.1-2001, Chapter
5, File Format Notation.
FUTURE DIRECTIONS
None.
SEE ALSO
awk , bc , echo , the System Interfaces volume of
IEEE Std 1003.1-2001, printf()
COPYRIGHT
Portions of this text are reprinted and reproduced in
electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 printf(P)
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