I'm trying to delete any line in a text file with certain text, and here's what I have:

write $+(-dw*,mydeleteword,*) mytextfile.txt

The only problem is, whenever a line is found with that phrase, it deletes the entire file! How can I make it only delete the one line.

/write -dw*matchtext* mytextfile.txt

first off
write $+( -dw*,mydeleteword,*) mytextfile.txt

the -dw doesn't belong inside the $+()

That worked perfectly! But I have another problem!

More than one instance of my search text exsists in the file, how do I delete all of them, not just one.

/filter

if your file is named test.txt it would be like this
//filter -ffcx test.txt test.txt *matchtext*

/help /filter

there is a lot of options that you can use