Re: [lopsa-discuss] A sed challenge

[Jesse Trucks]

Phil,

That is impressively obfuscated.
Jesse


jtru...@lopsa.org
Director, LOPSA
http://lopsa.org




On Nov 30, 2009, at 11:16 PM, Phil Pennock wrote:

-- Jesse Trucks, GCUX

On 2009-11-30 at 21:20 -0500, Tom Limoncelli wrote:

I have a file called rc-addition that contains:


# BEGIN project
a
bunch
of
lines
# END project



it and append the new text to the end.

This sounds like a job of sed but my sed fu is weak.

I want to append it to the end of /etc/rc.machine but if there is already a "# BEGIN project" / "# END project" it should replace that text, or delete

See, you're editing a file.  I do wonder why people fixate on stream
processing tools for editing a file, when there are command-line

stream-orientated.

The only trick parts are:
(1) one line, so no here-script, so need portable echo with newline
    interpretation, so use printf
(2) A marked line disappears once deleted, so to preserve line need to
    go back one, which would fail if "# BEGIN project" is on the first

    end.
(3) For portability, putting a single-quote into the middle of a
    single-quoted string in shell requires using '"'"' -- using
    double-quotes means escaping the $ instead.  Choose your poison.



One line, 139 characters.

136 if you remove the H\n at the start, but diagnostics are good.

All hail the one true Unix text-editor!

Regards,
-Phil
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interfaces available to script file-editing. And no, {sed -i} is still line; thus we insert a dummy line at the start and delete it at the printf 'H\n1\ni\nX\n.\n$\nka\ng/^# BEGIN project$/-\\\nka\\\n+1,/^# END project/d\n'"'"'ar rc-addition\n1d\nw\nq\n' | ed -s /etc/ rc.machine

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