Re: [gentoo-user] About sed

[Rafael Barreto]

For that I understood, this command will return the line of CLOCK= in
/etc/conf.f/clock without any comments. Is this right? Well, what I really
want is replace just CLOCK="fool1" by CLOCK="fool2" keeping the comments in
line.

By the way, \1 do really what? If i put \0 the result is the entire line.
So, could you explain me this a little more? Thanks...

2005/11/7, gentuxx <gentuxx@×××××.com>:
>
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> Willie Wong wrote:
>
> >On Mon, Nov 07, 2005 at 01:44:42AM -0200, Rafael Barreto wrote:
> >
> >>Hi,
> >>
> >>I'm learning about the use of the sed command and I have some
> questions. I'm
> >>trying to read in /etc/conf.d/clock the CLOCK variable with:
> >>
> >>sed '/^CLOCK="*"$/p' /etc/conf.d/clock
> >>
> >>This command, in principe, must print in screen the line that contains
> >>CLOCK= in the begin, contains anything between double quotes and ends.
> Well,
> >>this doesn't return anything. If I enter the above command without $,
> all is
> >>ok. But, if I would like to return just that line contains
> CLOCK="anything"
> >>and nothing more? For example,
> >
> >
> >No it doesn't. What you want is the regexp ^CLOCK=".*"$ if you want
> >anything (including nothing) between the double quotes, or
> >^CLOCK=".+"$ if you want something (excluding nothing) between the
> >double quotes.
> >
> >The reason that removing the trailing $ worked is that it matched the
> >CLOCK=" part, the * character specifies 0 or more iterates of the
> >previous character, which is "
> >
> >HTH
> >
> >W
>
> Also, as you pointed out, lines with trailing comments would not be
> returned based on the expression (even as modified):
>
> sed '/^CLOCK=".*"$/p /etc/conf.d/clock
>
> This is because the expression, as is, does not allow for anything
> after the last double quote ("). The following expression should
> match the line you want, and print out ONLY the 'CLOCK="foo"':
>
> sed -n '/^CLOCK=/s/^\(CLOCK=".*"\).*$/\1/p /etc/conf.d/clock
>
> How this works is as follows (since you're trying to learn sed):
>
> 1) the '-n' suppresses all output except that which was changed by
> your expression/commands.
> 2) the first expression ( /^CLOCK=/ ) gives sed the "address" at which
> to make the changes.
> 3) the second expression ( s/^\(CLOCK=".*"\).*$/\1/p )tells sed what
> to do when it reaches that address. This is better broken down into
> smaller steps:
> a) the first half of the substitution expression (
> s/^\(CLOCK=".*"\).*$/ ) tells sed to match the capital letters C
> - -L-O-C-K which start a line ( ^ ),
> b) followed by an equals sign (=), a double-quote ("),
> c) followed by 0 or more of any character type - except newlines
> - - ( .* ),
> d) followed by another double-quote (").
> e) Then, because of the parentheses metacharacters ( \( \) ),
> store the match in the holding space (memory).
> f) Then match 0 or more of any character type ( .* ), ending the
> line ( $ ).
> g) the second half ( /\1/ ) substitutes the characters "captured"
> in the parentheses metacharacters, for the whole line
> h) and prints ( /p ) the result
>
> So, while Willie's suggestion is correct, this should give you a more
> complete solution.
>
> HTH
>
> - --
> gentux
> echo "hfouvyAdpy/ofu" | perl -pe 's/(.)/chr(ord($1)-1)/ge'
>
> gentux's gpg fingerprint ==> 34CE 2E97 40C7 EF6E EC40 9795 2D81 924A
> 6996 0993
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