perl -nlE "push @res,/\[(\d+):(\d+)\](\w+)/?map{$3.qq([$_])}$2..$1:$_;END{say for @res}" portbus.txt

##</code><code>##


# some number is different
cat portbus.txt
[15:0]abc
[3:0]def
ghi
jkl
[3:0]mno
[6:0]pqr
stu
etc

perl -nlE "push @res,/\[(\d+):(\d+)\](\w+)/?map{$3.qq([$_])}$2..$1:$_;END{say for @res}" portbus.txt

abc[0]
abc[1]
abc[2]
abc[3]
abc[4]
abc[5]
abc[6]
abc[7]
abc[8]
abc[9]
abc[10]
abc[11]
abc[12]
abc[13]
abc[14]
abc[15]
def[0]
def[1]
def[2]
def[3]
ghi
jkl
mno[0]
mno[1]
mno[2]
mno[3]
pqr[0]
pqr[1]
pqr[2]
pqr[3]
pqr[4]
pqr[5]
pqr[6]
stu
etc



##</code><code>##

perl -nlE "say for/\[(\d+):(\d+)\](\w+)/?map{$3.qq([$_])}$2..$1:$_" portbus.txt