ed is a line-oriented text editor that has two modes: command mode and input mode. In command mode characters on the
standard input are interpreted as commands, and in input mode they are interpreted as text.
Explain the details of error conditions rather than the default ``?'' on the standard
error.
-o, --output
Write output to the standard output and error messages to the standard error. By default output
is written to the file being edited and error messages are printed on the standard output.
-p, --prompt=string
Sets the command line prompt to string. The default is no prompt.
-q, --test
For testing; enable verbose messages and reset the QUIT signal handler to the default
action.
-s, --silent
Disable verbose messages.
-O, --lenient
Enable lenient regular expression interpretation. This is the default if getconf
CONFORMANCE is not standard.
-S, --strict
Enable strict regular expression interpretation. This is the default if getconf CONFORMANCE
is standard. You'd be suprised what the lenient mode lets by.