my $text = do { local $/; <> };
$text =~ tr/\n//d;
$text =~ s/(.{80})/$1\n/g;
$text =~ s/(?!<\n)\z/\n/;
print($text);

##</code><code>##

perl script.pl infile > outfile

##</code><code>##

perl -i.bak script.pl file

##</code><code>##

ISA*00*          *00*          *28*9000000454     *ZZ*J00370         *070926*034
2*U*00401*000489661*0*P*:~GS*HP*9000000454*J00370*20070926*03421826*489660*X*004
010X091A1~ST*835*489662~BPR*I*6519.36*C*ACH*CCP*01*075906003*DA*0000194917*13518
40597*00454    *01*021000021*DA*304677450*20070926~TRN*1*EFT2545408*1351840597*0
0454~DTM*405*20070925~N1*PR*NATIONAL GOVERNMENT SERVICES  00454~N3*5151 CAMINO R
UIZ~N4*CAMARILLO*CA*930128645~REF*2U*00454~N1*PE*GOLDEN LIVINGCENTER FOLEY*FI*20
4120517~N3*1000 FIANNA WAY~N4*FORT SMITH*AR*72919~REF*PQ*015032~LX*210712~TS3*01
5032*21*20071231*8*19760.22*9175.8*10584.42**8905.8**-2334****9175.8*2604*******
8*8905.8~TS2*11509.8**********2*41*41~CLP*0073294416 070299289*19*856.96*769.14*
*MA*20725800001702*21*2~CAS*CO*94*-284.18~CAS*PR*2*372*0~NM1*QC*1*BRADY*LEO*F***
HN*140079398A~NM1*82*2*GOLDEN LIVINGCENTER FOLEY*****XX*1538110192~NM1*TT*2*WPS 
- TRICARE FOR LIFE*****PI*000060000~MIA*0***1141.14*MA02**********3*****MA44~REF
*EA*0073294416~DTM*050*20070913~DTM*23