Either of the literals  "\\\\" or  '\\\\' interpolate in a  m// or  qr// operator to a pair of backslash characters  \\ (escaped-backslash) which match a single backslash character.

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"print '\\';
 print '\\\\';
 print qq{\\};
 print qq{\\\\};
 ;;
 print qr{\\};
 my $bb = '\\\\';
 print qr{$bb};
 ;;
 my $PathOnly = 'c:\Dir1\Dir2\Dir3';
 ;;
 my @SubDirs = split(m/\\/, $PathOnly);
 dd \@SubDirs;
 ;;
 @SubDirs = split($bb, $PathOnly);
 dd \@SubDirs;
"
\
\\
\
\\
(?-xism:\\)
(?-xism:\\)
["c:", "Dir1", "Dir2", "Dir3"]

["c:", "Dir1", "Dir2", "Dir3"]
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