From type/independent-routines

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multi sub sprintf(Cool:D $format, *@args)

Returns a string according to a format as described below. The format used is the invocant (if called in method form) or the first argument (if called as a routine).

sprintf( "%s the %d%s", "þor", 1, "st").put; # OUTPUT: «þor the 1st␤» 
sprintf( "%s is %s", "þor", "mighty").put;   # OUTPUT: «þor is mighty␤» 
"%s's weight is %.2f %s".sprintf( "Mjölnir", 3.3392, "kg").put;
# OUTPUT: «Mjölnir's weight is 3.34 kg␤» 
# OUTPUT: «Mjölnir's weight is 3.34 kg␤»

This function is mostly identical to the C library's sprintf and printf functions. The only difference between the two functions is that sprintf returns a string while the printf function writes to a filehandle. sprintf returns a Str, not a literal.

The $format is scanned for % characters. Any % introduces a format token. Directives guide the use (if any) of the arguments. When a directive other than % is used, it indicates how the next argument passed is to be formatted into the string to be created. Parameter indexes may also be used in the format tokens. They take the form N$ and are explained in more detail below.

The $format may be defined enclosed in single or double quotes. The double-quoted $format string is interpolated before being scanned and any embedded string whose interpolated value contains a % character will cause an exception. For example:

my $prod = "Ab-%x-42";
my $cost = "30";
sprintf("Product $prod; cost: \$%d", $cost).put;
# OUTPUT: «Your printf-style directives specify 2 arguments, but 1 argument was supplied␤» 
          «  in block <unit> at <unknown file> line 1␤»

When handling unknown input you should avoid using such syntax by putting all variables in the *@args array and have one % for each in $format. If you need to include a $ symbol in the format string (even as a parameter index) either escape it or use the single-quoted form. For example, either of the following forms works without error:

sprintf("2 x \$20 = \$%d", 2*20).put; # OUTPUT: «2 x $20 = $40␤» 
sprintf('2 x $20 = $%d', 2*20).put;   # OUTPUT: «2 x $20 = $40␤» 

In summary, unless you need something very special, you will have fewer unexpected problems by using the single-quoted format string and not using interpolated strings inside the format string.

^[1]

From type/Cool

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method sprintf(*@args)

Returns a string according to a series format directives that are common in many languages; the object will be the format string, while the supplied arguments will be what's going to be formatted according to it.

"% 6s".sprintf('Þor').say; # OUTPUT: «   Þor␤»