Shell Programming and Scripting

Friends,
I have a file with contents like:

interface Serial0/4/0/0/1/1/1/1:0
encapsulation mfr
multilink
group 101
interface Serial0/4/0/0/1/1/1/2:0
encapsulation ppp
multilink
group 101

I just have to repace mfr with ppp and ppp with mfr in a single shot.

I tried using this:
awk '{gsub(/mfr/,"ppp");{gsub(/ppp/,"mfr")}}; 1'

But this 1st replaces mfr with ppp and then ppp with mfr, so finally i get all mfr.

Can somebody help me with this? Can we use SED?

Code:

awk '
     /mfr/ {gsub(/mfr/,"ppp"); print; next}
     /ppp/ {gsub(/ppp/,"mfr"); print; next}
     {print}
' infile

# or sed

sed '/ppp/ {s/ppp/mfr/g; n}; /mfr/ {s/mfr/ppp/g; n}' infile

Thanks zaxxon, it works.

if there will be more than one fmr or ppp occured per line, maybe below perl one is a choosable solution.

Code:

my %hash=(good=>'bad',bad=>'good');
while(<DATA>){
	chomp;
	my @tmp=split;
	print join " ", map {$hash{$_}?$hash{$_}:$_} @tmp;
	print "\n";
}
__DATA__
good bad hello good bad
bad hi good bad good
good how are good bad you bad
bad bad good good ohho