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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
formatted 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 internationalization 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
categories.)
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 messages
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:
1. 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.
2. A ' ' character in the format string shall be treated as a ' ' character, not as a <space>.
3. 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 number.
4. The implementation shall not precede or follow output from the d or u conversion specifiers with
<blank>s not specified by the format operand.
5. The implementation shall not precede output from the o conversion specifier with zeros not specified
by the format operand.
6. The e , E , f , g , and G conversion specifiers need not be supported.
7. 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 supported:
* The escape sequences listed in the Base Definitions 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 precision is omitted, it shall be taken to be
infinite, so all bytes up to the end of the converted string shall be written.
8. 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.
9. The format operand shall be reused as often as necessary to satisfy the argument operands. Any extra
c or 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
format operand contains no conversion specifications and argument operands are present, the results
are unspecified.
10. If a character sequence in the format operand begins with a '%' character, but does not form a valid
conversion 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 accumulated 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 performs floating-point calculations and
provides its own printf function. The bc utility can perform arbitrary-precision floating-point
arithmetic, but does not provide 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() function defined in the System Interfaces volume of
IEEE Std 1003.1-2001 on which it is based, makes no special 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 specification. Applications should be extremely cautious using either of these features when
there are multi-byte characters in the character set.
No provision is made in this volume of IEEE Std 1003.1-2001 which allows field widths and precisions 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 character. In the ISO C standard, the "##" 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 printf utility has a chance to parse the end of the hexadecimal constant.
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 corresponding conversion specification, the 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.
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
supplied by printf to satisfy the last %4d conversion specification.
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 standard output is what would be expected as the return
value from the strtol() function as defined in the System 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 character 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 versions of echo extant, the version has few
special features, 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 Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .