Re: blank lines as "^\s*$"

After posting the reply I saw the typo(line-2), & then while fixing it re-wrote the regex.
sed -e '
/[^ \t]/,$!d
/[^ \t]/b
:a
$d
N
/\n[ \t]*$/ba
' yourfile


--- In [email protected], "RAKESH" <sharma__r@...> wrote:
>
> 
> Thanks for the detailed distinctions in blank lines vs. the empty ones. Although I was aware of the differences(hence mentioned upfront my assumptions), and chose to use the /^$/ variety since it doesn't get in the way of the sed code in terms of legibility.
> 
> recapitulating, (i.e., /^$/ based )
> #-----------------------------
> /./,$!d
> /./b
> :a
> $d
> N
> /\n\n*$/ba
> #-----------------------------
> 
> Now this is how the above would appear using the /^\s*$/ approach
> Note: repl. \t => literal TAB since "sed" doesn't support \t
> and there's no way to show it's a TAB otherwise in here.
> #------------------------------------------
> /[^ \t]/,$!d
> /[^ \t/b
> :a
> $d
> N
> h
> s/.*\n//
> /^[ \t]*$/{
> g;ba
> }
> g
> #------------------------------------------
> 
> Notice the complexity increase in this case, which is due to fact that "sed" doesn't come armed with the \s \S regexes, otherwise this would have been a breeze, as you yourself state.
> 
> Just so that the OP gets an idea of a sed-based flow is why I chose the code that I gave. Once the hang of that is got, then the OP can upgrade to the /^\s*$/ approach if needed.
> 
> Rakehs
> 
> --- In [email protected], Sven Guckes <maillists-yahoo@> wrote:
> >
> > * Rakesh Sharma <sharma__r@> [2013-07-05 14:15]:
> > > Note: blank line => /^$/ i.e.,
> > > one which has no characters,
> > > not even spaces &/or TABs in it.
> > 
> > well, a line with *no* characters in it i'd call "empty".
> > 
> > so - here's my definition of "blank lines":
> > a "blank line" is contains only "blank characters";
> > "blank characters" are characters
> > which do not show up with any dots
> > (unless a font gives them any dots).
> > 
> > an empty line is a special case of a blank line
> > because all characters contained are "blank".
> > it is certainly valid for every contained element
> > as there are none for which it requires such quality.
> > (okay.. a little bit of set logic here..)
> > 
> > you may define a subset of these blank characters
> > to be valid only, eg spaces and tabs.
> > 
> > in the editor vim you can use the pattern "\s" for these.
> > (i think the notation of '\s' has been taken from
> > "perl compatible regular expressions" aka PCRE.)
> > 
> > so "blank lines" match the pattern "^\s*$"
> > which also matches with empty lines.
> > 
> > too bad we dont have "anchors" for
> > "start of data" and "end of data".
> > these would probably make the
> > given problem a breeze.
> > 
> > Sven
> > 
> > -- 
> > $ man 7 regex
> > Standard character class names are:
> > alnum alpha blank cntrl digit graph
> > lower print punct space upper xdigit
> >
>