Re: [9fans] ed regular expressions in sam

[revcomninos]

Thank you. Those distinctions are very helpful. I agree that thinking in terms 
of lines is easier to reason about. I am going to have to change some of my 
thinking and break old habits. 
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Re: [9fans] ed regular expressions in sam

[Silas McCroskey]

> I have yet gotten to this usage of "g" after "s".

The key difference here is not in the behavior of suffixed 'g', but in
how selections are made and operated on in the first place.

Ed's "selection" (aka dot, as you can reference it with '.') is always
a full, single line. It can *iterate* over multiple lines with
prefixed 'g', but each command (e.g. 's') will be run against only one
line at a time. As a result, suffixed 'g' always means "allow multiple
edits within this line" (alternatively, *not* suffixing with 'g' means
"only edit the first occurence of each line").

Sam's "selection" is more arbitrary -- it can be (and frequently is)
less than a line or multiple lines at once. In this case 'g' takes on
a different meaning -- "allow multiple edits within this selection" --
meaning if you *don't* pass 'g', and you're working with a multi-line
selection, only the first match in the entire selection will be
changed by the 's', regardless of whether other matches occurred on
separate lines.

As rob pointed out, interposing an 'x' without a regex will split the
selection into lines and iterate over each, getting you back to the
line-at-a-time behavior that is often easier to reason about.

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Re: [9fans] ed regular expressions in sam

[revcomninos]

Thank you for the clarification. This first usage conforms to ed. I am 
currently working slowly through "A Tutorial for the Sam Command Language" 
http://doc.cat-v.org/bell_labs/sam_lang_tutorial/ but I have yet gotten to this 
usage of "g" after "s".
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Re: [9fans] ed regular expressions in sam

[Silas]

In sam, g has two uses - either as a guard or after an s command where all 
substitutions are made

Quoting sam(1) (available at )
after an s command:
> If the command is followed by a g, as in
>    s/x/y/g, all matches in the range are substituted.
as a guard:
> g/regexp/ command
> v/regexp/ command
>    If the range contains (g) or does not contain (v) a
>    match for the expression, set dot to the range and run
>    the command.

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Re: [9fans] ed regular expressions in sam

[revcomninos]

I.e. in sam. In ed, g is frequently used at the end of the line. 
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Re: [9fans] ed regular expressions in sam

[revcomninos]

Thank you all for your responses. They were extremely helpful. The first 
example, which uses "g" threw me a little because I am not used to "g" at the 
end of the line. I presume it here means something like, "without changing the 
value of dot?"
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Re: [9fans] ed regular expressions in sam

[Rob Pike]

I would

,x s/.*/echo "&"/

as it seems most direct. The ,x idiom is the thing that turns sam into ed.

-rob


On Tue, Jul 20, 2021 at 9:18 PM  wrote:

> or:
> 
> ,x/^/i/echo "
> ,x/$/i/"
> 

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Re: [9fans] ed regular expressions in sam

[umbraticus]

or:

,x/^/i/echo "
,x/$/i/"


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Re: [9fans] ed regular expressions in sam

[revcomninos]

Thank you. I will test this an revert back.
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Re: [9fans] ed regular expressions in sam

[Alex Musolino]

> In ed it is trivial to edit either side of a line such as changing
> the line,
> 
> I use sam and ed
> 
> to,
> 
> echo "I use sam and ed."
> 
> simply with,
> 
> g/.*/s//echo "&."/
> 
> I am trying to figure out how to do the same in sam. 

,s/^.*$/echo "&."/g

or, perhaps closer to your ed example:

,x/^.*$/s//echo "&."/


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[9fans] ed regular expressions in sam

[revcomninos]

In ed it is trivial to edit either side of a line such as changing the line,

I use sam and ed

to,

echo "I use sam and ed."

simply with,

g/.*/s//echo "&."/

I am trying to figure out how to do the same in sam. 


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