Multiline substitution to obtain a tree view - bash

Question

I have a bash script that generates the following output from a certain input using sed and `awk:
# ├── CHILDA1
# │ └── CHILDB1
# │ └── CHILDB2
# │ └── CHILDB3
# │ └── CHILDB4
# │ └── CHILDB5
# │ └── CHILDB6
# │ └── CHILDC1
# │ └── CHILDC2
# │ └── CHILDB7
# ├── CHILDA2
# └──────────────
Is there a way to replace the nest connectors, if they are not the last one, in order to obtain something like this?
# ├──┐CHILDA1
# │ ├── CHILDB1
# │ ├── CHILDB2
# │ ├── CHILDB3
# │ ├── CHILDB4
# │ ├── CHILDB5
# │ ├──┐CHILDB6
# │ │ ├── CHILDC1
# │ │ └── CHILDC2
# │ └── CHILDB7
# ├── CHILDA2
# └──────────────
The first output has been obtained with simple single lines substitutions, I guess the second one needs to check for the row above at the same column (character position). I don't know how tree handles this, but the result I would like to obtain is very similar.
Unicode characters obtained from https://en.wikipedia.org/wiki/Box_Drawing

Answer 1

It would be easier to process the file from the bottom up. This can be achieved using tac.
Through #flags, the following tracks the position of children whose parent has not yet been encountered.
tac |
perl -CSD -Mutf8 -pe'
if ( /[└├]/ ) {
my $i = $-[0]; # Position of the match.
substr($_, $i, 1, "├") if $flags[$i];
$flags[$i] = 1;
my $j = $i+3; # Position of its children.
substr($_, $j, 1, "┐") if $flags[$j];
$flags[$j] = 0;
while ( $i-- ) {
substr($_, $i, 1, "│") if $flags[$i];
}
}
' |
tac
Output
# ├── CHILDA1
# │ ├── CHILDB1
# │ ├── CHILDB2
# │ ├── CHILDB3
# │ ├── CHILDB4
# │ ├── CHILDB5
# │ ├──┐CHILDB6
# │ │ ├── CHILDC1
# │ │ └── CHILDC2
# │ └── CHILDB7
# ├── CHILDA2
# └──────────────
All in Perl:
perl -CSD -Mutf8 -e'
my #lines = reverse <>;
for ( #lines ) {
if ( /[└├]/ ) {
my $i = $-[0]; # Position of the match.
substr($_, $i, 1, "├") if $flags[$i];
$flags[$i] = 1;
my $j = $i+3; # Position of its children.
substr($_, $j, 1, "┐") if $flags[$j];
$flags[$j] = 0;
while ( $i-- ) {
substr($_, $i, 1, "│") if $flags[$i];
}
}
}
print reverse #lines;
'