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Perl - Grep function regular expression

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# 1  
Old 08-18-2010
Perl - Grep function regular expression
For some reason,
@logs is a list of log files
@filter is a list of expressions to grep out
Code:
foreach (@logs){
open READ, "<$_" or die $!;
@temp=<READ>;
close READ;

    foreach (@filter){
        print grep /$_/,@temp ;    
        
}
}

returns a regex error in one of the files it's parsing.

while
Code:
print grep $_,@temp ;

returns the entire file

while
Code:
print grep /string/,@temp ;

works fine.


I can not seem to wrap my head around it today. Any clues?
# 2  
Old 08-19-2010
what u wanna get actualy?
you just opening every file and reading it then trying to grep some filter-shit from it's content..
is it what u want?
i'm not sure if grep can work for the whole array..
why not to do it when u actualy opened the file and while($line=<FILE>){grep it} ?
anyway try to use $somevar, not $_
tip78
# 3  
Old 08-19-2010
Try to use the list context , ex (not tested):

Code:
foreach (@logs){
open READ, "<$_" or die $!;
@temp=<READ>;
close READ;

    foreach $var (@filter){
          @u=(@u,grep /$var/,@temp );    
        
}
}

foreach $u (@u){ print "u:".$u."\n"; }

# 4  
Old 08-19-2010
Everything you have checked is right.. Understand as mentioned below.

Quote:
Originally Posted by adelsin
For some reason,
@logs is a list of log files
@filter is a list of expressions to grep out
Code:
foreach (@logs){
open READ, "<$_" or die $!;
@temp=<READ>;
close READ;

    foreach (@filter){
        print grep /$_/,@temp ;    
        
}
}

returns a regex error in one of the files it's parsing.
When the file has a line with just single open paranthesis, then you will get regex error ?! What is the big deal in this ?

If you want to avoid then escape it using either quotemeta function, or use \Q. Using some input directly as regex is not good, as you have this risk.
Quote:
Originally Posted by adelsin
while
Code:
print grep $_,@temp ;

returns the entire file
What does grep will do ? If for current iteration the return value is true then the current $_ will be pushed in to the result array, so you get the entire array, as each time you have some value at $_ and that returns true.

Quote:
Originally Posted by adelsin
while
Code:
print grep /string/,@temp ;

works fine.






I can not seem to wrap my head around it today. Any clues?

If you dont understand the basics, you will end up in confusions.
# 5  
Old 08-19-2010
Quote:
When the file has a line with just single open paranthesis, then you will get regex error ?! What is the big deal in this ?
It would exit the program at this point.

I ended up having to go with passing $_ to a scalar variable and then placing the scalar variable into an array.

Code:
foreach (@logs){
open READ, "<$_" or die $!;
@temp=<READ>;
close READ;
    foreach (@filter){
        my $alt=$_;
        print grep {/\Q$alt\E/i} @temp ;    
        }
}

Thank you all for your help.


Quote:
If you dont understand the basics, you will end up in confusions.
This is why I'm here. I was able to figure out the problem after I thought about what was happening for awhile and researched how the grep() function operated. And remembered about Quotemetas.


Just out of curiosity, when I do the following:
Code:
foreach (@logs){
open READ, "<$_" or die $!;
#@temp=<READ>;
        foreach (@filter){
        my $alt=$_;
        print grep {/\Q$alt\E/i} <READ>;    
        }
close READ; 
}

It seems not to go through the @filter array, but rather only the first value of it. Why would this be when trying to read directly from the file?
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