All I want to do is. . .
. . .use ed.
How to use
ed, a line oriented text editor.
ed sample.txt sample.txt: No such file or directory
The message above warns that the sample.txt file is newly created.
a the quick brown fox jumped over the lazy dog .
That was an append command, which added text to the file.
The dot on a line by itself terminated the append.
On line 1, replace the first substring matching an f followed by a lowercase alphabetic followed by x with ‘dragon’. The substitute command accepts basic regular expressions.
the quick brown dragon jumped over the lazy dog
Print all lines from 1 to the last.
That wrote the file to disk. The ‘q’ command ends the editing session.