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 ...?
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INTRODUCTION

       This  command  generates a formatted string in a fashion similar to the ANSI C sprintf procedure.  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 character is a % then it is not copied to the result string.  Instead, the characters following the  %
       character are treated as a conversion specifier.  The conversion specifier controls the conversion of the next successive arg to a particu-
       lar format and the result is appended to the result string in place of the conversion specifier.  If there are multiple	conversion  speci-
       fiers  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 specifier, a set of flags, a minimum field width, a  pre-
       cision,	a  size modifier, and a conversion 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 convert is not taken from the next  sequential  argument.
       Instead, it is taken from the argument 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 successive 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 characters, 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 is not 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 conver-
		 sions, 0x or 0X (respectively) will be added to the beginning of the result unless it is zero.  For  all  floating-point  conver-
		 sions	(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 decimal 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 an integer value.

       The  fourth  portion of a conversion specifier is a precision, which consists of a period followed by a number.	The number is used in dif-
       ferent 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 (how-
       ever, trailing zeroes after the decimal point will still be omitted unless the # flag has been specified).   For  integer  conversions,	it
       specifies a minimum number of digits to print (leading zeroes will be added if necessary).  For s conversions it specifies the maximum num-
       ber of characters to be printed; if the string is longer than this then the trailing characters will be dropped.  If the precision is spec-
       ified 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 size modifier, which must be ll, h, or l.  If it is ll it specifies that an integer value is
       taken without truncation for conversion to a formatted substring.  If it is h it specifies that an integer value is truncated to  a  16-bit
       range  before  converting.  This option is rarely useful.  If it is l it specifies that the integer value is truncated to the same range as
       that produced by the wide() function of the expr command (at least a 64-bit range).  If neither h nor l are present, the integer  value	is
       truncated  to  the  same  range	as that produced by the int() function of the expr command (at least a 32-bit range, but determined by the
       value of tcl_platform(wordSize)).

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

       d	 Convert integer to signed decimal string.

       u	 Convert integer to unsigned decimal string.

       i	 Convert integer to signed decimal string (equivalent to d).

       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  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 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 number as for %e or %E.  Otherwise con-
		 vert as for %f.  Trailing zeroes and a trailing decimal point are omitted.

       %	 No conversion: just insert %.

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 supported.

       [2]    For %c conversions the argument must be an integer value, which will then be converted to the corresponding character value.

       [3]    The size modifiers are ignored when formatting floating-point values.  The ll modifier has no sprintf counterpart.

EXAMPLES

       Convert the numeric value of a UNICODE character to the character itself:
	      set value 120
	      set char [format %c $value]

       Convert the output of time into seconds to an accuracy of hundredths of a second:
	      set us [lindex [time $someTclCode] 0]
	      puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]

       Create a packed X11 literal color specification:
	      # Each color-component should be in range (0..255)
	      set color [format "#%02x%02x%02x" $r $g $b]

       Use XPG3 format codes to allow reordering of fields (a technique that is often used in localized  message  catalogs;  see  msgcat)  without
       reordering the data values passed to format:
	      set fmt1 "Today, %d shares in %s were bought at $%.2f each"
	      puts [format $fmt1 123 "Global BigCorp" 19.37]

	      set fmt2 "Bought %2$s equity ($%3$.2f x %1$d) today"
	      puts [format $fmt2 123 "Global BigCorp" 19.37]

       Print a small table of powers of three:
	      # Set up the column widths
	      set w1 5
	      set w2 10

	      # Make a nice header (with separator) for the table first
	      set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
	      puts $sep
	      puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
	      puts $sep

	      # Print the contents of the table
	      set p 1
	      for {set i 0} {$i<=20} {incr i} {
		 puts [format "| %*d | %*ld |" $w1 $i $w2 $p]
		 set p [expr {wide($p) * 3}]
	      }

	      # Finish off by printing the separator again
	      puts $sep

SEE ALSO

       scan(n), sprintf(3), string(n)

KEYWORDS

       conversion specifier, format, sprintf, string, substitution

Tcl									8.1								 format(n)