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format(n)			      Tcl Built-In Commands				format(n)

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NAME
       format - Format a string in the style of sprintf

SYNOPSIS
       format formatString ?arg arg ...?
_________________________________________________________________

INTRODUCTION
       This  command generates a formatted string in the same way as the ANSI C sprintf procedure
       (it uses sprintf in its implementation).  FormatString indicates how to format the result,
       using % conversion specifiers as in sprintf, and the additional arguments, if any, provide
       values to be substituted into the result.  The return value from format is  the	formatted
       string.

DETAILS ON FORMATTING
       The command operates by scanning formatString from left to right.  Each character from the
       format string is appended to the result string unless it is a percent sign.  If the  char-
       acter  is a % then it is not copied to the result string.  Instead, the characters follow-
       ing the % character are treated as a conversion specifier.  The conversion specifier  con-
       trols  the  conversion of the next successive arg to a particular format and the result is
       appended to the result string in place of the conversion specifier.  If there are multiple
       conversion  specifiers  in the format string, then each one controls the conversion of one
       additional arg.	The format command must be given enough args to meet the needs of all  of
       the conversion specifiers in formatString.

       Each  conversion  specifier may contain up to six different parts: an XPG3 position speci-
       fier, a set of flags, a minimum field width, a precision, a length modifier, and a conver-
       sion  character.   Any of these fields may be omitted except for the conversion character.
       The fields that are present must appear in the order given above.   The	paragraphs  below
       discuss each of these fields in turn.

       If  the	% is followed by a decimal number and a $, as in ``%2$d'', then the value to con-
       vert is not taken from the next sequential argument.  Instead, it is taken from the  argu-
       ment  indicated	by  the  number, where 1 corresponds to the first arg.	If the conversion
       specifier requires multiple arguments because of * characters in the specifier  then  suc-
       cessive	arguments are used, starting with the argument given by the number.  This follows
       the XPG3 conventions for positional specifiers.	If there are any positional specifiers in
       formatString then all of the specifiers must be positional.

       The second portion of a conversion specifier may contain any of the following flag charac-
       ters, in any order:

       -	 Specifies that the converted argument should  be  left-justified  in  its  field
		 (numbers are normally right-justified with leading spaces if needed).

       +	 Specifies that a number should always be printed with a sign, even if positive.

       space	 Specifies  that  a  space  should be added to the beginning of the number if the
		 first character isn't a sign.

       0	 Specifies that the number should be padded on the left with  zeroes  instead  of
		 spaces.

       #	 Requests  an  alternate  output form. For o and O conversions it guarantees that
		 the first digit is always 0.  For x or X conversions, 0x  or  0X  (respectively)
		 will  be added to the beginning of the result unless it is zero.  For all float-
		 ing-point conversions (e, E, f, g, and G) it guarantees that the  result  always
		 has  a decimal point.	For g and G conversions it specifies that trailing zeroes
		 should not be removed.

       The third portion of a conversion specifier is a number giving a minimum field  width  for
       this  conversion.   It is typically used to make columns line up in tabular printouts.  If
       the converted argument contains fewer characters than the minimum field width then it will
       be  padded  so  that it is as wide as the minimum field width.  Padding normally occurs by
       adding extra spaces on the left of the converted argument, but the 0 and -  flags  may  be
       used to specify padding with zeroes on the left or with spaces on the right, respectively.
       If the minimum field width is specified as * rather than a number, then the next  argument
       to the format command determines the minimum field width; it must be a numeric string.

       The  fourth  portion  of a conversion specifier is a precision, which consists of a period
       followed by a number.  The number is used in different  ways  for  different  conversions.
       For  e,	E,  and f conversions it specifies the number of digits to appear to the right of
       the decimal point.  For g and G conversions it specifies the total  number  of  digits  to
       appear, including those on both sides of the decimal point (however, trailing zeroes after
       the decimal point will still be omitted unless the # flag has been specified).  For  inte-
       ger  conversions, it specifies a minimum number of digits to print (leading zeroes will be
       added if necessary).  For s conversions it specifies the maximum number of  characters  to
       be  printed;  if  the  string  is  longer  than	this then the trailing characters will be
       dropped.  If the precision is specified with * rather than a number then the next argument
       to the format command determines the precision; it must be a numeric string.

       The  fifth  part of a conversion specifier is a length modifier, which must be h or l.  If
       it is h it specifies that the numeric value should be truncated to a 16-bit  value  before
       converting.  This option is rarely useful.  If it is l it specifies that the numeric value |
       should be (at least) a 64-bit value.  If neither h or l are present,  numeric  values  are |
       interpreted  as	being  values  of  the	width of the native machine word, as described by |
       tcl_platform(wordSize).

       The last thing in a conversion specifier is an alphabetic character that  determines  what
       kind  of  conversion  to  perform.  The following conversion characters are currently sup-
       ported:

       d	 Convert integer to signed decimal string.

       u	 Convert integer to unsigned decimal string.

       i	 Convert integer to signed decimal string;  the integer may either be in decimal,
		 in octal (with a leading 0) or in hexadecimal (with a leading 0x).

       o	 Convert integer to unsigned octal string.

       x or X	 Convert    integer    to    unsigned	 hexadecimal	string,    using   digits
		 ``0123456789abcdef'' for x and ``0123456789ABCDEF'' for X).			  |

       c											  |
		 Convert integer to the Unicode character it represents.

       s	 No conversion; just insert string.

       f	 Convert floating-point number to signed decimal string of the form xx.yyy, where
		 the number of y's is determined by the precision (default: 6).  If the precision
		 is 0 then no decimal point is output.

       e or e	 Convert floating-point number to scientific notation  in  the	form  x.yyye+-zz,
		 where	the  number  of  y's is determined by the precision (default: 6).  If the
		 precision is 0 then no decimal point is output.  If the E form is used then E is
		 printed instead of e.

       g or G	 If  the exponent is less than -4 or greater than or equal to the precision, then
		 convert floating-point number as for %e or %E.  Otherwise  convert  as  for  %f.
		 Trailing zeroes and a trailing decimal point are omitted.

       %	 No conversion: just insert %.

       For the numerical conversions the argument being converted must be an integer or floating-
       point string; format converts the argument to binary and then converts it back to a string
       according to the conversion specifier.

DIFFERENCES FROM ANSI SPRINTF
       The  behavior of the format command is the same as the ANSI C sprintf procedure except for
       the following differences:

       [1]    %p and %n specifiers are not currently supported.

       [2]    For %c conversions the argument must be a decimal string, which will then  be  con-
	      verted to the corresponding character value.

       [3]    The l modifier is ignored for real values and on 64-bit platforms, which are always |
	      converted as if the l modifier were present (i.e. the types  double  and	long  are |
	      used for the internal representation of real and integer values, respectively).  If
	      the h modifier is specified then integer values are truncated to short before  con-
	      version.	Both h and l modifiers are ignored on all other conversions.

SEE ALSO
       sprintf(3), string(n)

KEYWORDS
       conversion specifier, format, sprintf, string, substitution

Tcl					       8.1					format(n)
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