Echoing stdin when running an ed(1) script

Question

Given the following ed script,

$ cat helloworld
a
hello
world
.
,n
,s,o,O,g
,n
Q

I would like to obtain somehow the interactive output

$ ed
a
hello
world
.
,n
1   hello
2   world
,s,o,O,g
,n
1   hellO
2   wOrld
Q
$

instead of the expected

$ cat helloworld | ed
1   hello
2   world
1   hellO
2   wOrld
$

Is that possible, maybe using a third-party utility? Thanks in advance!

Edit: I guess I should add some motivation. I would like to produce some sample ed sessions, and probably save them with script(1). If this process is performed "live", any modifications would basically imply typing the whole tutorial again (bad) or alternatively "figuring out" the output, potentially based on a long editing session (worse).

Answer 1

It sounds like you want to simulate an interactive terminal session, in which the user types a command, waits for a response (or, given that the target is ed, sometimes waits for a response), then types another command, etc. You could write an expect script to do this, but it may be good enough to just send a line at a time to both the terminal and the target process, with a brief pause between each line.

    $ while IFS= read -r line
      do
        printf '%s\n' "$line" >/dev/tty
        printf '%s\n' "$line"
        sleep 0.5
      done < helloworld | ed
a
hello
world
.
,n
1   hello
2   world
,s,o,O,g
,n
1   hellO
2   wOrld
Q

To better distinguish input from output, you could add color or other highlighting to the
echo "$line" >/dev/tty line, or, in this particular case, enable the prompt character in ed (the P command) so that a * will show up in front of each ed command.

Answer 2

Well, after monkeying around with it, this is what I'd use:

 awk '{ print; system("sleep 0") }' edscript | tee /dev/tty | ed

or, without tee:

awk '{ print >"/dev/stderr"; print | "ed"; system("sleep 0") }' edscript

If print >"/dev/stderr" doesn't work on your system you could use print | "cat >&2".

---

With gnu sed:

sed -u -n -e 'p;w /dev/stderr' -e 's|.*||e' edscript | ed

---

Another way that works just as well:
Use split to split your edscript on each line:

split -l1 edscript

this will produce pieces like xaa, xab...xah.
You could then use the pieces like this:

for i in x*; do awk '{ print >"/dev/stderr"; print }' $i; done | ed

or

for i in x*; do sed -n -e 'p;w /dev/stderr' $i; done | ed

to get the expected result. Then you rm x*...

Answer 3

I did something... complicated. I've been looking into ex/ed recently - I'm not very good with either - and this marked an opportunity to dive a little deeper. This parses the ed script first and passes it off to ed in-stream:

b='[:blank:]'
sed -e 'h;/\n/!i\' -e 0i -e 's/^\(.*[^\]\)*\(\\\\\)*\\$//;tn'"
/^\n*\([0-9;$,.$b]*[gGvV].*\\\\\n[$b]*\)*\([0-9,$.;${b}]*[aic][$b]*\)\
\(\n\(.*\)\n\.\)*\(\n.*\)*$/{ s//\4/;:n" -e 'G;//{N;D
    };g;s//\1\2/;l;x;s//\4/;l;H;s/.*/./;a\' -e '.
};l;g;i\' -e .\\ -e 1,.p\\ -e u <ed_script | ed

It is less complicated then before - and now virtually all of the complication lies in a single regex spanning two lines. That one long regex handles virtually all of the testing for the entire script.

The idea is that, as near as I can tell, you can only get to insert mode with one of either the append, insert, or change commands. insert mode then takes all input literally up to the next occurring line consisting of only a . dot. Any other continued command that spans multiple lines - even a sequence of such where G, g, V, or v are involved - is necessarily continued to the next line with a trailing \backslash - though, as usual, a \backslash escapes itself in that context.

So, while it's entirely possible I'm mistaken, I think this handles all cases. For every input line that doesn't match a [aic] ... . dot series sed inserts a series of commands that looks like:

0i
command-line$
.
1,.p
u

...instructing ed to insert an unequivocal look (as written by sed) at its own command, then to print it, and last to undo the whole operation - which has the very convenient result of getting the edit done, printing it, reversing it, and restoring the last address in a single action.

For those that lines that do match in a sequence of either trailing backslashes or an [aic] ... . series it is a little more complicated. In those cases sed recursively pulls them in until it encounters the end of the series before doing its look. I was careful to separate the [aic], ., and actual literal input into separate prints - each of those types will get its own look - such that the literal input is strung together as much as possible (sed will break a look output at 80 chars by default).

I guess it's easier just to show you. You'll notice the ? prompt below - this occurs because the g command given before it is not valid command - not because sed mangles the input (I hope). Here is the output from a modified version of your example dataset:

g \\\n  a$
hello\nworld\\\n\n  0a\n  world\\\nworld\nworld$
.$
?
,n$
1       hello
2       world\
3
4         0a
5         world\
6       world
7       world
,s,o,O,g$
4$
  0a
.,$n$
4         0a
5         wOrld\
6       wOrld
7       wOrld
,s,$,\\\n\\\n\\\\$
\
,n$
1       hellO
2
3       \
4       wOrld\
5
6       \
7
8
9       \
10        0a
11
12      \
13        wOrld\
14
15      \
16      wOrld
17
18      \
19      wOrld
20
21      \
Q$