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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 a fashion similar to the ANSI C sprintf procedure.  For-matString FormatString
       matString 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 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  argu-ments arguments
       ments  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 charac-ter character
                 ter 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 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 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 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 conver-sions conversions
       sions 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 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 sub-string. substring.
       string.  If it is h it specifies that an integer value is truncated to a 16-bit range before convert-ing. converting.
       ing.   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 con-version conversion
       version 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 (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 convert as for %f.  Trailing zeroes and a trailing deci-mal decimal
                 mal 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 follow-ing following
       ing 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 mes-sage message
       sage 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)