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Linux 2.6 - man page for printf (linux section 1posix)

PRINTF(P)			    POSIX Programmer's Manual				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 op-
       erands 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, Inter-
	      nationalization 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 interna-
	      tionalization 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 argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic 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  sup-
	      ported).

       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  excep-
       tions:

	1. A <space> in the format string, in any context other than a flag of a conversion spec-
	   ification, 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  num-
	   ber.

	4. The implementation shall not precede or follow output from the d or u conversion spec-
	   ifiers 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 unspeci-
       fied.

       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 speci-
	   fied below.

	9. The format operand shall be reused as often as necessary to satisfy the argument oper-
	   ands.  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 specifi-
	   cations 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 speci-
       fier 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 per-
       form arbitrary-precision floating-point arithmetic, but does not provide extensive format-
       ting 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  deal-
       ing with multi-byte characters when using the %c conversion specification or when a preci-
       sion 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 char-
       acter 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 op-
       erand 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 hexa-
       decimal 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 charac-
       ters 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 cor-
       rectly, 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 imple-
       mentation 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 Defi-
       nitions 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					PRINTF(P)


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