format(3tcl)                  Tcl Built-In Commands                 format(3tcl)


       format - Format a string in the style of sprintf

       format formatString ?arg arg ...?

       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.

       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 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 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 b conversions,
                 0b 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 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 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 the wordSize element
       of the tcl_platform array).

       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 (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).

       b         Convert integer to unsigned binary string, using digits 0 and

       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

       e or E    Convert 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 number as for %e or %E.  Otherwise
                 convert as for %f.  Trailing zeroes and a trailing decimal
                 point are omitted.

       %         No conversion: just insert %.

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

       [1]    Tcl guarantees that it will be working with UNICODE characters.

       [2]    %p and %n specifiers are not supported.

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

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

       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

              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

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

       conversion specifier, format, sprintf, string, substitution

Tcl                                    8.1                          format(3tcl)