"sed" question - undocumented features like comments

[Guy Harris]

> Gee, I tried running a script with multiple lines of comments sprinkled
> throughout it on the 4.2 and S5 "sed"s and they both worked exactly the
> same...  First *line*?  I don't believe anybody'd be so sloppy as to require
> all comments to fit into *one* line.

I checked up on it and -- good grief, they *were* that sloppy.  It turns out
that the S5 "sed" we're running here has the Berkeley comment code stuck in.
The change is trivial; change line 171 of "sed0.c" (or thereabouts; it's
line 171 in the S5R2V1 VAX distribution) from

	if(*cp == '\0')  continue;

to

	if(*cp == '\0' || *cp == '#')    continue;

Your line numbers may differ on V7, S3, other S5's, etc..

Note that 1) if you continue a command on multiple lines using \, "#" at the
beginning of those continuation lines will NOT be treated as a comment
indicator, and 2) "#" in the middle of a command (i.e., not at the beginning
of a line or separated from the beginning of the line only by whitespace)
will also not be treated as a comment indicator.  This is a feature; it
means that old scripts won't break by virtue of "#" characters which used to
be legitimate parts of commands suddenly becoming comments....

Also note that, even in "sed"s without this code, you shouldn't have the
first line of a script be a comment which immediately follows the "#" and
begins with a lower-case "n" unless you want the script always to be run as
if "sed" had been invoked with the "-n" flag.  If the first two characters
of a script are "#n", it turns on the "-n" flag, as mentioned before...

	Guy Harris