I liked the general idea of your solution.

Minor quibbles:
-don't use $a and $b - these are special Perl variables reserved for things like sorting, etc and are predefined global variables. You won't write much Perl before this gets you into trouble.
-dealing with "space" can be tricky as say " \t" may not be so apparent. I would prefer \s+ as the split parameter (one or more space characters [ \t\f\r\n])

#/usr/bin/perl -w
use strict;

my $in ='HWI-1KL120:99:C0C9MACXX:6:1101:2105:2123 0 chr5 75483987 0 82
+M3I16M * 0 0';

my ($fifth, $sixth) = (split(/\s+|:/,$in) )[5,6];

print "$fifth:$sixth\n"; #2105:2123

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In reply to Re^2: problem in splitting the line by Marshall
in thread problem in splitting the line by devi

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