[TUHS] ed: multiple addresses (with semicolons)

markus schnalke meillo at marmaro.de
Fri Jul 8 18:09:47 AEST 2022


now I did find nroff sources to the manpages of earlier editions
-- still learning about the organization of the code on the TUHS

Already in the 1st Edition the ed(1) manpage writes:

	Commands may require zero, one, or two addresses.  Commands
	which require no addresses regard the presence of an
	address as an error. Commands which require the presence of
	one address all assume a default address (often ".") but if
	given more than one address ignore any extras and use the
	last given. Commands which require two addresses have
	defaults in the case of zero or one address but use the
	last two if more than two are given.

Hence this features was already present from the beginning. My
question must thus shift to QED: Was it present there as well or
was it newly introduced to ed? As it is not listed as a
differences to QED, it seems to have been taken from there

My interest in general use cases and stories around the feature
is still present. ;-)


[2022-07-08 09:47] markus schnalke <meillo at marmaro.de>
> Hoi,
> via a recent message from Chris Pinnock to the list I became aware
> of the book ``Ed Mastery'' by Michael W. Lucas. At once I bought
> and read it. Although it is not on the mastery level it claims and
> I would have liked it to be, it still was fun to read.
> This brought me back to my ed interest. I like ed a lot and despite
> my young age, I've actually programmed with ed for fun and have
> prepared the troff slides for a talk on early Unix tools (like ed)
> with ed alone. I use the Heirloom version of ed.
> Anyways, I wondered about the possibility to give multiple
> addresses ... more than two for relative address searches.
> For example, to print the context of the first occurance of `argv'
> within the main function, you can use:
> 	/^main(/;/\<argv\>/-2;+4n 
> For the last occurance it's even one level more:
> 	/^main(/;/^}/;?\<argv\>?-2;+4n
> (The semicolons mean that the next search or relative addressing
> starts at the result of the previous one. I.e. in this case: We go
> to the `main' function, from there go to the function end, then
> backwards to `argv' minus two lines and print (with line numbers)
> this line and four lines more.)
> The manpage of 6th Edition mentiones this possibility to give more
> than two addresses:
> 	Commands may require zero, one, or two addresses.  Commands
> 	which require no addresses regard the presence of an address
> 	as an error.  Commands which accept one or two addresses
> 	assume default addresses when insufficient are given.  If
> 	more addresses are given than such a command requires, the
> 	last one or two (depending on what is accepted) are used.
> 	http://man.cat-v.org/unix-6th/1/ed
> You can see it in the sources as well:
> 	https://www.tuhs.org/cgi-bin/utree.pl?file=V6/usr/source/s1/ed.c
> (Search for  ';'  to find the line. There's a loop processing the
> addresses.)
> V5 ed(1) is in assembler, however, which I cannot read. Thus there
> must have been a complete rewrite, maybe introducing this feature
> at that point. (I don't know where to find v5 manpage to check
> that as well.)
> I wonder how using multiple addresses for setting starting points
> for relative searches came to be. When was it implemented and what
> use cases drove this features back in the days? Or was it more an
> accident that was introduced by the implementation, which turned
> out to be useful? Or maybe it existed already in earlier versions
> of ed, althoug maybe undocumented.
> For reference, POSIX writes:
> 	Commands accept zero, one, or two addresses. If more than the
> 	required number of addresses are provided to a command that
> 	requires zero addresses, it shall be an error. Otherwise, if more
> 	than the required number of addresses are provided to a command,
> 	the addresses specified first shall be evaluated and then discarded
> 	until the maximum number of valid addresses remain, for the
> 	specified command.
> 	https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ed.html
> Here more explanation rom the rationale section:
> 	Any number of addresses can be provided to commands taking
> 	addresses; for example, "1,2,3,4,5p" prints lines 4 and 5, because
> 	two is the greatest valid number of addresses accepted by the print
> 	command. This, in combination with the <semicolon> delimiter,
> 	permits users to create commands based on ordered patterns in the
> 	file. For example, the command "3;/foo/;+2p" will display the first
> 	line after line 3 that contains the pattern foo, plus the next two
> 	lines. Note that the address "3;" must still be evaluated before
> 	being discarded, because the search origin for the "/foo/" command
> 	depends on this.
> As far as I can see, multiple addresses make only sense with the
> semicolon separator, because the comma separator does not change
> the state, thus previous addresses can have no effect on later
> addresses. The implementation just does not forbid them, for
> simplicity reasons.
> meillo

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