Using sed to append a line with alt characters - bash

Question

I have this file I want to add a line with and I seem to have a problem when using alt characters.
Here's the script piece:
#testfile.txt
Main
├────►projectA
└────►projectC
sed "/├────►projectA/a ├────►projectB/" testfile.txt
sed doesn't seem to find the "├────►projectA" portion. Grep won't even find it.
grep "├────►projectA" testfile.txt
grep returns nothing.
So how can you make it found so I can add my line below it?
Edit: I found my problem. I was using the wrong character in my sed command. This script is on a different system so I had to make an example off the top of my head.
I'm trying to add spaces as well after the /a but it trims it. Is there a way to preserve the spaces?
(e.g. "[5 spaces] ├────►projectB")
I can't add spaces to the above line because stakoverflow formatting trims it as well. So I say [5 spaces] to represent the amount of whitespace.

Answer 1

It seems to me like you're trying to use sed to append a literal string (i,.e. a string containing any characters) but sed doesn't understand literal strings, only regular expressions and backreference-enabled replacements, see Is it possible to escape regex metacharacters reliably with sed. You should instead be using a tool like awk that understands literal strings.
Is this all you want to do?
$ awk '{print} index($0,"├────►projectA"){print "├────►projectB"}' file
#testfile.txt
Main
├────►projectA
├────►projectB
└────►projectC
If you want 5 leading blanks, just add 5 leading blanks to the string in the print statement:
$ awk '{print} index($0,"├────►projectA"){print " ├────►projectB"}' file
#testfile.txt
Main
├────►projectA
├────►projectB
└────►projectC
If you just want to duplicate whatever indent the preceding line has, here's a modified version of your input file:
$ cat file
#testfile.txt
Main
├────►projectA
└────►projectC
and here's how to print the new line with whatever indent (blanks and/or tabs) the preceding line uses:
$ awk '{print} s=index($0,"├────►projectA"){print substr($0,1,s-1) "├────►projectB"}' file
#testfile.txt
Main
├────►projectA
├────►projectB
└────►projectC

Answer 2

This might work for you (GNU sed):
sed '/^├────►projectA$/{p;s/A/B/}' file
Match on ────►projectA, print the line then substitute B for A.
Use the sed command l0 to see each lines representation in octal and ascii.
Thus this is the same as above:
sed '/^\o342\o224\o234\o342\o224\o200\o342\o224\o200\o342\o224\o200\o342\o224\o200\o342\o226\o272projectA$/{p;s/A/B/}' file
To add 5 spaces to front of such a line, use:
sed '/^├────►projectA$/{p;s/^/ /;s/A/B/}' file
Or you may prefer:
sed '/^\(├────►project\)A$/{p;s/ \1B/}' file