Newbie help with sed

[bluegroper]

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

 

[hoinz]

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

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...

 

[hoinz]

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

 

[geirendre]

Some helpfull links

http://www.ibm.com/developerworks/linux/library/l-sed1.html

http://www.oreilly.com/catalog/sed2/

http://www.grymoire.com/Unix/Sed.html

http://sed.sourceforge.net/sed1line.txt

http://www.cornerstonemag.com/sed/

 

[pavNell]

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.

 

[stevexff]

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

[small]"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:erlDesignPatterns)[/small]