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


       format - Format a string in the style of sprintf

       format formatString ?arg arg ...?

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

       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 speci-
       fier 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  addi-
       tional  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 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 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 characters, in any order:

       -         Specifies that the converted argument should  be  left-justi-
                 fied  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 con-
                 versions, 0x or 0X (respectively) will be added to the begin-
                 ning 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 spec-
                 ifies that trailing zeroes should not be removed.

       The  third portion of a conversion specifier is a number giving a mini-
       mum field width for this conversion.  It  is  typically  used  to  make
       columns  line  up in tabular printouts.  If the converted argument con-
       tains fewer characters than the minimum field width  then  it  will  be
       padded  so that it is as wide as the minimum field width.  Padding nor-
       mally occurs by adding extra spaces on the left of the converted  argu-
       ment,  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 argu-
       ment 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 con-
       sists of a period followed by a number.  The number is used in  differ-
       ent  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 char-
       acters to be printed; if the string is longer than this then the trail-
       ing 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.  The l modifier is ignored.

       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;  the integer may
                 either be in decimal, in octal (with a leading 0) or in  hex-
                 adecimal (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 deci-
                 mal 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  deci-
                 mal 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 conver-
       sion specifier.

       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;  integer values are always  converted
              as  if there were no modifier present and real values are always
              converted as if the l modifier were present (i.e. type double is
              used  for  the  internal  representation).  If the h modifier is
              specified then integer values are truncated to short before con-

       sprintf(3), string(n)

       conversion specifier, format, sprintf, string, substitution

Tcl                                   8.1                            format(n)