Powershell .split and append while keeping split format - string

Question

Hello my question is how do i keep the format for a string that has had the .split run on it. What i want
$test="a.b.c.d.e"
$test2="abc"
#split test
#append split to test2
#desired output
abc
a
b
c
d
e
I know if i perform split on a string such as
$test="a.b.c.d.e"
$splittest=$test.split(".")
$splittest
#output
a
b
c
d
e
However when i try to make it so that i want to append the above split to a string
$test2="abc"
$test2+$splittest
#output
abca b c d e
while
$splittest+$abc
#output
a
b
c
d
e
abc
Is there a way to append the split string to another string while keeping this split format or will i have to foreach loop through the split string and append it to the $test2 string one by one.
foreach ($line in $splittest)
{
$test2="$($test2)`n$(splittest)"
}
I would prefer not to use the foreach method as it seems to slow down a script i am working on which requires text to be split and appended over 500k times on the small end.

Answer 1

What you're seeing is the effect of how PowerShell's operator overload resolution.
When PowerShell sees +, it needs to decide whether + means sum (1 + 1 = 2), concatenate (1 + 1 = "11"), or add (1 + 1 = [1,1]) in the given context.
It does so by looking at the type of the left hand side argument, and attempts to convert the right hand side argument to a type that the chosen operator overload expects.
When you use + in the order you need, the string value is to the left, and so it results in a string concatenation operation.
There are multiple ways of prepending the string to the existing array:
# Convert scalar to array before +
$newarray = #($abc) + $splittest
# Flatten items inside an array subexpression
$newarray = #($abc;$splittest)
Now all you have to do is join the strings by a newline:
$newarray -join [System.Environment]::NewLine
Or you can change the output field separator ($OFS) to a newline and have it joined implicitly:
$OFS = [System.Environment]::NewLine
"$newarray"
Finally, you could pipe the array to Out-String, but that will add a trailing newline to the entire string:
#($abc;$splittest) |Out-String