C:\>perl -E "my $num ='abcd23.5fghi';if ($num =~ /[a-z]+(.*?)[a-z]/i){ say $1;}"
23.5                                                      /^\

##</code><code>##

C:\>perl -E "my $num ='abcd23.5fghi';if ($num =~ /[a-z]+(.*)[a-z]/i){ say $1;}"
23.5fgh    # not what OP seems to want

##</code><code>##

C:\>perl -E "my $num ='abcd23fghi'; my $intermediate; if ($num =~ /[a-d]+(\d+)[f-z]+/) {$intermediate = $1;} if ($intermediate =~ /[0-9]+/ ){ say $intermediate;}"
23

##</code><code>##

C:\>perl -E "my $num ='abcd23.777fghi'; my $intermediate; if ($num =~ /[a-d]+(\d+)[f-z]+/) {$intermediate = $1;} if ($intermediate =~ /[0-9]+/ ){ say $intermediate;}"
(no output)