[TUHS] ed: multiple addresses (with semicolons)

[TUHS] ed: multiple addresses (with semicolons)

[markus schnalke]

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

[TUHS] Re: ed: multiple addresses (with semicolons)

[markus schnalke]

Hoi,

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

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
unchanged.


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


meillo



[2022-07-08 09:47] markus schnalke <meillo@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
> 

[TUHS] ed: multiple addresses (with semicolons)

[Douglas McIlroy]

The interpretation of a string of addresses separated by commas and/or
semicolons was already defined in the v1 man page for ed.

Ed was essentially a stripped-down version of Multics qed. The latter
was originally
written by Ken. Unfortunately the "Multics Condensed Guide" online at
multicians.org describes how strings of addresses were interpreted
only by canonical examples for the various editing requests.

I  have no specific memory of semicolons in qed. I have a vague
recollection that semicolons originated in ed, however you should put
no trust in this. Maybe Ken remembers.

Doug