As it so happens, blakem and myself were playing with some (obfuscated?) code to perform just this task (precision formatting) for an array of numbers in this thread here. The best I think that I was able to come up with was this:

sub a{$_=int$_[0]*10**$_[1];s;(.{$_[1]})$;\.$1;;return$_};
[download]

This subroutine, while not particularly robust, takes two arguments, the number to format and the formatting precision - For example, the following code formats to single decimal precision:

my @a = ("1.10", "2.22");
print STDOUT &a($_, 1) for @a;

sub a{$_=int$_[0]*10**$_[1];s;(.{$_[1]})$;\.$1;;return$_};
[download]

 

Update: After running this code through the test-suite written by Albannach, I would probably modify my subroutine as follows to clean up the subroutine output so that a trailing '.' isn't left at the end of a number if there is no decimals to follow it and to add rounding:

sub a{$_=int$_[0]*10**$_[1]+.5;s;(.{$_[1]})$;\.$1;;chop if substr($_,-
+1)eq'.';return$_};
[download]

And the result ...

value|precision     sprintf   Incognito   Albannach       jeffa      r
+ob_au
 '123.45678'|3:     123.457     123.456     123.456         123     12
+3.457
      '12.4'|1:        12.4        12.4        12.4          12       
+ 12.4
          ''|0:           0                                           
+    0
      '3.14'|5:     3.14000     3.14000     3.14000    00003.14     3.
+14000
         '1'|5:     1.00000     1.00000     1.00000       00001     1.
+00000
        '.5'|0:           0                                           
+    1
        '10'|5:    10.00000    10.00000    10.00000       00010    10.
+00000
  '12.45435'|0:          12          12          12          12       
+   12
       '100'|5:   100.00000   100.00000   100.00000       00100   100.
+00000
        '3.'|0:           3           3           3           3       
+    3
      '1000'|5:  1000.00000  1000.00000  1000.00000       01000  1000.
+00000
     '12.56'|0:          13          12          12          12       
+   13
[download]

 

Ooohhh, Rob no beer function well without!