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PRINTF(1P)		   POSIX Programmer's Manual		    PRINTF(1P)

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.

NAME
       printf — write formatted output

SYNOPSIS
       printf format [argument...]

DESCRIPTION
       The printf utility shall write formatted operands to the standard  out‐
       put. The argument operands shall be formatted under control of the for‐
       mat 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 con‐
		 trol 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 vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
		 ables 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 POSIX.1‐2008, Chapter 5, File	 Format	 Nota‐
       tion 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 charac‐
	   ter that is copied to the output.

	2. A  '' character in the format string shall be treated as a '' char‐
	   acter, not as a <space>.

	3. In addition to the escape sequences shown in the  Base  Definitions
	   volume  of  POSIX.1‐2008,  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> characters 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	a,  A,	e, E, f, 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	<back‐
	   slash>-escape sequences shall be supported:

	   --  The  escape  sequences listed in the Base Definitions volume of
	       POSIX.1‐2008, 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 contain‐
	       ing it, any remaining string operands, and any additional char‐
	       acters 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 speci‐
	   fication 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  conver‐
	   sion	 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.

       11. The argument to the c conversion specifier can be a string contain‐
	   ing 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.

       The argument operands shall be treated as strings if the	 corresponding
       conversion specifier is b, c, or s, and shall be evaluated as if by the
       strtod() function if the corresponding conversion specifier is a, A, e,
       E,  f,  F, g, or G.  Otherwise, they shall be evaluated as unsuffixed C
       integer constants, as described by the ISO C standard, with the follow‐
       ing extensions:

	*  A leading <plus-sign> 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.

	*  Suffixed integer constants may be allowed.

       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.

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  POSIX.1‐2008 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 POSIX.1‐2008 which allows	 field
       widths  and  precisions	to  be	specified  as '*' since the '*' can be
       replaced directly in the format operand using shell variable  substitu‐
       tion.  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  lim‐
       ited  to,  at  most, three octal digits, but hexadecimal character con‐
       stants 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 conver‐
       sion  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-comple‐
       ment 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 con‐
       vey 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 POSIX.1‐2008. 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 code‐
       set, 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	 stan‐
	     dard codeset

       43    Numeric  value of the character '+' in the ISO/IEC 646:1991 stan‐
	     dard codeset

       45    Numeric value of the character '−' in the ISO/IEC 646:1991	 stan‐
	     dard codeset

       Note  that in a locale with multi-byte characters, the value of a char‐
       acter is intended to be the value of the equivalent of the wchar_t rep‐
       resentation of the character as described in the System Interfaces vol‐
       ume of POSIX.1‐2008.

RATIONALE
       The printf utility was added to provide functionality that has histori‐
       cally  been  provided  by echo.	However, due to irreconcilable differ‐
       ences in the various versions of echo extant, the version has few  spe‐
       cial 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
       POSIX.1‐2008, Chapter 5, File Format Notation.

       Earlier versions of this standard specified that arguments for all con‐
       versions other than b, c, and 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 conver‐
       sions 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 distin‐
       guishing 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 strtod(), 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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       awk, bc, echo

       The Base Definitions volume of POSIX.1‐2008,  Chapter  5,  File	Format
       Notation, Chapter 8, Environment Variables

       The System Interfaces volume of POSIX.1‐2008, fprintf(), strtod()

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 Electri‐
       cal  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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			    PRINTF(1P)
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