How can I expand a string like "1..15,16" into a list of numbers?

Question

I have a Perl application that takes from command line an input as:

application --fields 1-6,8

I am required to display the fields as requested by the user on command line.

I thought of substituting '-' with '..' so that I can store them in array e.g.

$str = "1..15,16" ;
@arr2 = ( $str ) ;
@arr = ( 1..15,16 ) ;
print "@arr\n" ;
print "@arr2\n" ;

The problem here is that @arr works fine ( as it should ) but in @arr2 the entire string is not expanded as array elements.

I have tried using escape sequences but no luck.

Can it be done this way?

Answer 1

Use split:

@parts = split(/\,/, $fields);

print $parts[0];
1-6
print $parts[1];
8

You can't just put a string containing ',' in an array, and expect it to turn to elements (except if you use some Perl black magic, but we won't go into that here)

But Regex and split are your friends.

Answer 2

@arr2 = ( eval $str ) ;

Works, though of course you have to be very careful with eval().

Answer 3

You could use eval:

$str = "1..15,16" ;
@arr2 = ( eval $str ) ;
@arr = ( 1..15,16 ) ;
print "@arr\n" ;
print "@arr2\n" ;

Although if this is user input, you'll probably want to do some validation on the input string first, to make sure they haven't input anything dodgy.

Answer 4

You're thinking of @arr2 = eval($str); Since you're taking input and evaluating that, you need to be careful. You should probably @arr2 = eval($str) if ($str =~ m/^[0-9.,]+$/)

P.S. I didn't know about the Number::Range package, but it's awesome. Number::Range ftw.

Answer 5

If this is user input, don't use string eval on it if you have any security concerns at all.

Try using Number::Range instead:

 use Number::Range;

 $str = "1..15,16" ;
 @arr2 = Number::Range->new( $str )->range;
 print for @arr2;

To avoid dying on an invalid range, do:

 eval { @arr2 = Number::Range->new( $str )->range; 1 } or your_error_handling

There's also Set::IntSpan, which uses - instead of ..:

 use Set::IntSpan;

 $str = "1-15,16";
 @arr2 = Set::IntSpan->new( $str )->elements;

but it requires the ranges to be in order and non-overlapping (it was written for use on .newsrc files, if anyone remembers what those are). It also allows infinite ranges (where the string starts -number or ends number-), which the elements method will croak on.