topic Re: how to remove content in a file in Operating System - HP-UX

how to remove content in a file

ust3 — Wed, 29 Aug 2007 05:55:25 GMT

I hv a text file that has 500000 lines , some lines begins the word "Error" , if I want to delete all lines except the lines begins the word "Error" ( that means only keep "Error" lines ) , what can I do ? thx

Re: how to remove content in a file

Pete Randall — Wed, 29 Aug 2007 06:01:21 GMT

grep "Error" filename > newfile

Pete

Re: how to remove content in a file

Marcin O. — Wed, 29 Aug 2007 06:02:19 GMT

Hi

ex.
cat file1 | grep "^Error" >file2

Marcin

Re: how to remove content in a file

James R. Ferguson — Wed, 29 Aug 2007 06:28:25 GMT

Hi:

Using 'grep' is certainly one way to do this. As shown by Marcin, you probably want to anchor your match to the beginning of the line since you said '...except lines [that begin with] the word "Error"'.

It is wasteful to 'cat' the file into a pipe to 'grep'. That adds another process!

You could also use Perl and to select lines beginning with "Error" and having a word-boundry on either side (\b).

# perl -ne 'print if /\bError\b/' file

Regards!

...JRF...

Re: how to remove content in a file

Marcin O. — Wed, 29 Aug 2007 07:12:44 GMT

Hi
Of course all above methods are correct, but I check speed of processing those three methods. If you interested in

1. only grep
2. cat+grep
3. perl
on file with 4M lines, result was:
1. 4.1s
2. 4.5s
3. 9.5s

Marcin

Re: how to remove content in a file

Hein van den Heuvel — Wed, 29 Aug 2007 07:49:42 GMT

ust3,

Please be VERY explicit about 'Error'.
Spelled EXACTLY so, or more upper/lower combinations
Exactly in the beginning of the line, or 'close' (how close!).
Or are you looking for 'Error' anywhere as seperate word(the first perl solution)?

Marcin,

Whiel you are trying... please re-try perl again with an anchorred RE where it does not have to scan the whole line:

# perl -ne 'print if /^Error/' file

Hein.

Re: how to remove content in a file

James R. Ferguson — Wed, 29 Aug 2007 07:54:21 GMT

Hi (again):

Ooops, thanks Hein, I beat the anchor drum and then mistyped myself :-{

Also, while I would expect Perl to have a small startup overhead, its value in cases like this lies in its superior regular expression engine.

Regards!

...JRF...

Re: how to remove content in a file

Sandman! — Wed, 29 Aug 2007 08:32:12 GMT

# awk '$0~/^Error/' file

Re: how to remove content in a file

Peter Nikitka — Wed, 29 Aug 2007 09:51:56 GMT

Hi,

even shorter as Sandman's solution:
awk '/^Error/' file

or taking '"Error" is the first word' into account:
awk '$1=="Error"' file

mfG Peter

Re: how to remove content in a file

Arturo Galbiati — Thu, 30 Aug 2007 02:33:56 GMT

Hi,
sed -n '/^Error/p' file

HTH,
Art