What would really help me is if you would rewrite

echo -e "abc\ndef\nghi\n" | perl -wlne '! /def/ and print "$_";'
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for me with "-we" in place of "-wple" with all the short hand and defaults removed so I could see exactly what is going on.

Perl does that for you, at least the part after the pipe char, if you load B::Deparse (comments mine):

qwurx [shmem] ~> perl -MO=Deparse,-x -wlne '! /def/ and print "$_";'
BEGIN { $^W = 1; }                   # this is -w
BEGIN { $/ = "\n"; $\ = "\n"; }      # this is -l
LINE: while (defined($_ = <ARGV>)) { # and here is what -n does...
    chomp $_;                        # this belongs to -l
    print "$_" unless /def/;
}                                    # this belongs to -n too
-e syntax OK
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The only line without comment is -e, i.e. your command line script body.

Here's another example - count lines, invented by Abigail:

perl -ne '}{ print $.'
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The }{ construct - named eskimo greeting - splits the implicit while loop into a while loop block and a bare block:

perl -MO=Deparse,-x -ne '}{print$.'
LINE: while (defined($_ = <ARGV>)) {  # -n
    ();                               # script body - a noop
}                                     # script body
{                                     # script body
    print $.;                         # script body
}                                     # -n
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The bare block is used to output the current line number of the (special) filehandle ARGV.