Anyway, to go through that code bit by bit, it's like this:

$/=\108;
($/) = (<> =~ /^.{105}(.?\r?\n?)/);
seek ARGV, 0, 0;
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or to be more understandable, but less terse:

# Look ahead into the file for the ISA segment and the few characters 
+which
#    follow it, so that we can determine the segment terminator charac
+ter(s).
$/ = \108;
my $ISA_and_trailing_chars = <>;

# examine the text after the segment for the segment termination chara
+cter(s)
$ISA_and_trailing_chars =~ /
    ^.{105}        # The actual ISA segment, itself
    (
        .?        # The proper segment terminator character
        \r?        # If the segment terminator is followed by a newlin
+e and/or
        \n?        #    carriage return, include that as part of the s
+egment
                #    terminator.  this isn't really legal to do, but s
+ome
                #    folks do it, regardless, and we want to be able t
+o handle
                #    that sort of garbage as though it weren't garbage
+.
    )
/x;
my $segment_terminator = $1;

# set the input record separator to the segment termination character(
+s), so
#    that subsequent reads from the file will read one segment at a ti
+me.
$/ = $segment_terminator;

# since we peeked ahead into the file, to determine *how* to read it, 
+now
#    seek back to the beginning of it, so that we can read it (all) co
+rrectly
seek ARGV, 0, 0;
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Hope that explains it better. For what it's worth, I actually updated the little script I use for this to also pull the field-separator and component-separator, too. I made a little shell-script wrapper around this, so that I can easily write simple little perl command-line scripts with the very basics of X12 syntax handling builtin. Here it is;

#!/bin/sh

# since "perl -p ... -n ..." will be treated by perl as just
# "perl -p ... ..." (not allowing the -n to override the -p)
# we have to scan through any switches on the command line,
# so that commands like "x12cat -ne 'print if /^PLB/' ..."
# will work as expected... but still allow an implicit "-p"
# if no "-n" is specified.  Granted this isn't perfect...
# But this isn't so bad, because an explicit "-p" can override
# this.
looptype=""
for i do
        case "$i" in
                -m*)    ;; # -m and -M start command-line "use" direct
+ives,
                -M*)    ;; # "n"s in them should be ignored
                -*n*)   looptype=n;;
                -h)             echo 'x12cat: "magic" x12 spooler wrap
+per around command-line perl.
  -splits files by segment terminator
  -auto sets $f and $c to (regex-escaped) field and component separato
+rs
  -auto sets the autosplit to the field separator (for the -a autospli
+t)
  -allows -pe or -ne operations on file (or none at all to just cat th
+e file)'; exit;;
                -*)             ;;
                *)              break;;
        esac
done
if [ "x$looptype" = "x" ]; then
        looptype=p
fi

perl -l -$looptype -e 'BEGIN{$SIG{PIPE}="exit"; $|=1; $/=\108; ($f,$c,
+$/)=(<> =~ /^ISA(.).{100}(.)(.?\r?\n?)/); ($f,$c)=("\Q$f","\Q$c"); se
+ek ARGV,0,0; $.=0}' -F'/$f/' "$@"
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The idea of that script (I call it x12cat) is that I can do fairly simple things like:

$ x12cat -ne 'print if /^GS/' some_file.x12
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to grep a file for GS segments. Or to do something more interesting (showing off how it ties into perls -a, or "autosplit", comand-line parameter):

$ x12cat -ane '$paid += $F[4] if $F[0] eq "CLP"; END{print $paid}' som
+e_835_file.x12
[download]

which would print the sum of all CLP04 fields (total amount paid in an 835 electronic remittance advice file).

------------
:Wq
Not an editor command: Wq
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