... I must know, how many backslashes in a row ...

A way:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = '\\\\\---\--\\\\---\\--\\\-';
 print qq{'$s'};
 ;;
 printf '   %d', $_ for map tr{\\}{}, $s =~ m{ \\+ }xmsg;
"
'\\\---\--\\---\--\\-'
   3   1   2   1   2
[download]

Update: map expression was  scalar(tr{\\}{\\}) but I realized scalar wasn't necessary.