how to remove specific lines from a file


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# 15  
Quote:
Originally Posted by bluemoon1
As my home work, I tried to figure it out how it works (though I know it works) but still no luck:-( Would someone elabrate a little of the syntax for me?[...]
In awk, uninitialized variables ("no" in our case) have the numeric value zero, which in awk means false
therefore the following code means IF (0) AND /str/ (the current record contains the pattern "str"), which means IF FALSE AND TRUE (true for the records that contain the pattern), then skip this record (that's the meaning of the "next" statement).
FALSE AND TRUE == FALSE (it would have been true if both elements were true), so, the records that contain the pattern "str" before we set the variable no to 1 (which in awk means TRUE) are not affected, nothing happens:

Code:
no&&/str/{next}

The following code means: if the current record contains the pattern "The F", assign the value 1 to the variable no, then skip the record ("next"):

Code:
/The F/{no=1;next}

Then we need just: 1 (TRUE), in awk this means use default action,
which is print the current record (not affected/skipped! by the previous actions):
Code:
1

We can write all this also as:

Code:
awk '/The F/,0{if($0~/str/)next}1' filename

(another homework Smilie)
# 16  
Dear radoulov

Thank you so much! Now that I understand how it works, I'm actually able to add a little more to it to solve the problem I had (removing all the lines including different keywords):
nawk 'no&&/str1|str2|str3|...../{next};/The F/{no=1;next}1' filename

However, when I tried to run this line it compaint syntax error:
awk '/The F/,0{if($0~/str/)next}1' filename

I tried to fix with no luck:-(
I think I was able to recognize the second part- if there is a matching pattern(str) found in current line($0), skip it(next) otherwise print (1).
But I don't know how to interpret the first half. Please help me;-)

Bluemoon
# 17  
Quote:
Originally Posted by bluemoon1
[...]
However, when I tried to run this line it compaint syntax error:
awk '/The F/,0{if($0~/str/)next}1' filename

I tried to fix with no luck:-(
If you are on Solaris, you have to use nawk or /usr/xpg4/bin/awk,
not the old broken /usr/bin/awk.

Quote:
I think I was able to recognize the second part- if there is a matching pattern(str) found in current line($0), skip it(next) otherwise print (1).
But I don't know how to interpret the first half. Please help me;-)
Right,
the first part is a range selector: start,end - from the pattern "The F" to 0 (0 is false, so to the end of the file(s)).
# 18  
Thanks radoulov! And yes, it works exactly as you described on Solaris:-)
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