Something along the lines of:
use feature ":5.14";
use warnings FATAL => qw(all);
use strict;
my ($c, $s) = (0, '');
for(split /\n/, << 'END')
LABEL#00001
MVC SYMBOL+2(4),X.PDES_KEY+2
+
MVC SYMB_ART,=C'XSEQ' //line comments
+
+
F$SFH SELECT,LISTING,
+ *
DESKART=SYMB_ART,
+ *
DESKWERT=SYMBOL,
+ *
MARKTCODE=L#MACF
+
BNE F03#000 //line comments
END
{if (length > 71 and substr($_, 71, 1) eq '*') # Detect continuation
{s/\A\s*// if $c == 1; # Strip leading space
+in continuation
s/\s*\*\s*\Z//; # Strip trailing space
($s, $c) = (($c ? $s : '').$_, 1); # Concatenate or resta
+rt depending on continuation state
}
else
{s/\A\s*// if $c == 1; # Strip leading spaces
+ in continuation
say "$s$_"; # Write completed stat
+ement
($s, $c) = ('', 0); # Restart
}
}
Produces
LABEL#00001
MVC SYMBOL+2(4),X.PDES_KEY+2
+
MVC SYMB_ART,=C'XSEQ' //line comments
+
+
F$SFH SELECT,LISTING,DESKART=SYMB_ART,DESKWERT=SYMBOL,MARKTCO
+DE=L#MACF
BNE F03#000 //line comments