Man Pages

printf(1p) - phpMan printf(1p) - phpMan

Command: man perldoc info search(apropos)  


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 dif-
       fer (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 output. The argument operands shall be for-
       matted 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 prece-
              dence 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 exam-
              ple, 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  writ-
              ten 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 For-
              mat Notation ( '\\', '\a', '\b', '\f', '\n', '\r', '\t', '\v' ), which shall be converted to the charac-
              ters 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


            * 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 con-
           version 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 exten-
       sions:

        * 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 specifica-
       tion.  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  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 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 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  APPLICA-
       TION  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 correspon-
       dence exists between %u and strtoul() and %e, %f, and %g (if the implementation supports floating-point conver-
       sions) 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                           PRINTF(1P)