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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 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
       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 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
       specifier, a set of flags, a minimum field width, a precision, a length  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 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
                 floating-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
       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 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 nor 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
       supported:

       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.yyyzz,
                 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
              converted 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
              conversion.  Both h and l modifiers are ignored on all other conversions.

EXAMPLES

       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(3tcl), sprintf(3), string(3tcl)

KEYWORDS

       conversion specifier, format, sprintf, string, substitution