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Newbie help with sed

Newbie help with sed

Newbie help with sed

(OP)
Hey forum
I've not used sed much.
When I pipe a text file to
| sed -n '4,$p'
What does sed actually do to the file ?
man sed did not help me at all.
TIA's


RE: Newbie help with sed

Why don't you try with a few files and find out yourself? wink

ok, here you go:
print (p) from fourth (4) to last ($) line.

I agree that reading man sed isn't easy. But it's worth it...

RE: Newbie help with sed

btw, for completeness's sake:
do not (-n) print other lines

RE: Newbie help with sed

Actually, it doesn't to anything to the text file. It just prints the results of the command to the screen. Also piping a text file into sed is not the most efficient way to use sed. Here's a better example and also overwrites the input file. Make a copy of text file first in case you screw it up.

line=`sed -e '4,$p' textfile.txt.bak 2>/dev/null`
echo "$line" > textfile.txt.bak

Hope this helps.

RE: Newbie help with sed

Quote (pavNell):

Also piping a text file into sed is not the most efficient way to use sed.
Piping stuff into sed is efficient enough for most purposes. Unless you've actually got a performance problem, don't fix it. It just obfuscates what you are trying to do.

[rant]
Personally, I can't stand all those bash/korn scripts that are  constantly shelling out to cut, sed, awk, and echo just to get the job done. If your scripting language can't cut it on it's own, pick one that can (hint: Perl)
[/rant]

Steve

"Every program can be reduced by one instruction, and every program has at least one bug. Therefore, any program can be reduced to one instruction which doesn't work." (Object::PerlDesignPatterns)

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