Shell Programming and Scripting

Please post error as well as script.

There is no error in the script you provided it is me who made the error when I wrote it. I had wrote num_type at the beginning and then sum_type for the print that is why I had no output.
Can you explain me what the script does exactly ?

Thanks.

Hi,

Code:

#!/usr/bin/perl

$filename=shift;   ## First command line argument (log file name) will come in $filename
$sum_type=shift;   ## second command line argument (Summary Type)  will come in $sum_type
chomp($sum_type,$filename);  ## The chomp() function will remove (usually) any newline character from the end of a string. 			     
open(FH,"<","$filename") || die "cannot open file \n";  ## open file for read else exit from the script

while (<FH>) {
chomp;
if (/\s$sum_type\sSUMMARY\s\[(\w+)\.\w+\]\s(\w+)\scnt\/(\d+)\s/) { 
## pattern matching with log file record


#\w  Match "word" character (alphanumeric plus "_")
#\W  Match non-word character
#\s  Match whitespace character
#\S  Match non-whitespace character
#\d  Match digit character
#\D  Match non-digit character

#*      Match 0 or more times
#+      Match 1 or more times
#?      Match 1 or 0 times

print "$sum_type SUMMARY $1 $2 $3 \n";

#$1 -  If record match with pattern then whatever in first "()" (i.e. (\w+) ) is $1
#$2 -  If record match with pattern then whatever in second "()" (i.e. (\w+) ) is $2
#$3 -  If record match with pattern then whatever in third "()" (i.e. (\d+) ) is $3

 
}
}
close(FH);

A big thanks to you pravin. It is really clear now

Hi Samb95

I can try to explain what pravin has done here.

Command line arguments are stored in the aray @ARGV in perl.

By doing a shift he is removing the elements and putting them in respective variables.

$firstname = shift;
$sum_type = shift;

Might i add its good practice to use "use strict" and "use warnings" modules and declare the variables preceded by a "my" keyword.

He then opens a file in read mode "<" and assigns it a file handler FH.

He loops through the file using FH. chomp removes the new line at the end of the input line read from the file.

Next you encounter the reg ex. looks formidable but simple. ( You should have a look at the reg exp tutorials ).

Since no argument is mentioned the reg ex acts on the $_ which contains the currernt input line of the file.

What he is doing is
1: \s$sum_type\sSUMMARY\s : looking for a space followed by your keyword followed by a space, the word SUMMARY followed by another space.

2: \[(\w+)\.\w+\]\s(\w+)\scnt\/(\d+)\s : escape the brackets to match an open square bracket.
Then look for one or more word characters (includes alphanumeric ) = \w+
Notice he has enclosed them in ( ) meaing it will be assigned to the perl special variable $1.

3: next he has matched a "." Since "." is a special character it has been escaped by a backslash. And the rest follow the similar analogy.

Hope this helps.

---------- Post updated at 10:27 AM ---------- Previous update was at 10:23 AM ----------

Just to be safe,

When ever you read command line arguments, your program should do checking to see if the user has entered the correct number of arguments. If not throw an error and quit the program.

Thanks for the advices and explanation abhijithtk, I will add them in the code.