Recursive grep in perl - perl

Question

I am new to perl. I have a directory structure. In each directory, I have a log file. I want to grep pattern from that file and do post processing. Right now I am grepping the pattern from those files using unix grep and putting into text file and reading that text file to do post processing, But I want to automate task of reading each file and grepping pattern from that file. In the code below the mdp_cgdis_1102.txt have grepped pattern from directories. I would really appreciate any help
#!usr/bin/perl
use strict;
use warnings;
open FILE, 'mdp_cgdis_1102.txt' or die "Cannot open file $!";
my #array = <FILE>;
my #arr;
my #brr;
foreach my $i (#array){
#arr = split (/\//, $i);
#brr = split (/\:/, $i);
print " $arr[0] --- $brr[2]";
}

Answer 1

It is unclear to me which part of the process needs automating. I'll go by "want to automate reading each file and grepping pattern from that file," whereby you presumably already have a list of files. If you actually need to build the file list as well see the added code below.
One way: pull all patterns from each file and store that in a hash (filename => arrayref-with-patterns)
my %file_pattern;
foreach my $file (#filelist) {
open my $fh, '<', $file or die "Can't open $file: $!";
$file_pattern{$file} = [ grep { /$pattern/ } <$fh> ];
close $fh;
}
The [ ] takes a reference to the list returned by grep, ie. constructs an "anonymous array", and that (reference) is assigned as a value to the $file key.
Now you can process your patterns, per log file
foreach my $filename (sort keys %file_pattern) {
print "Processing log $filename.\n";
my #patterns = #{$file_pattern{$filename}};
# Process the list of patterns in this log file
}
ADDED
In order to build the list of files #filelist used above, from a known list of directories, use core File::Find
module which recursively scans supplied directories and applies supplied subroutines
use File::Find;
find( { wanted => \&process_logs, preprocess => \&select_logs }, #dir_list);
Your subroutine process_logs() is applied to each file/directory that passed preprocessing by the second sub, with its name available as $File::Find::name, and in it you can either populate the hash with patterns-per-log as shown above, or run complete processing as needed.
Your subroutine select_logs() contains code to filter log files from all files in each directory, that File::Find would normally processes, so that process_file() only gets the log files.
Another way would be to use the other invocation
find(\&process_all, #dir_list);
where now the sub process_all() is applied to all entries (files and directories) found and thus this sub itself needs to ensure that it only processes the log files. See linked documentation.

Answer 2

The equivalent of
find ... -name '*.txt' -type f -exec grep ... {} +
is
use File::Find::Rule qw( );
my $base_dir_qfn = ...;
my $re = qr/.../;
my #log_qfns =
File::Find::Rule
->name(qr/\..txt\z/)
->file
->in($base_dir_qfn);
my $success = 1;
for my $log_qfn (#log_qfns) {
open(my $fh, '<', $log_qfn)
or do {
$success = 0;
warn("Can't open log file \"$log_qfn\": $!\n);
next;
};
while (<$fh>) {
print if /$re/;
}
}
exit(1) if !$success;

Answer 3

Use File::Find to traverse the directory.
In a loop go through all the logfiles:
Open the file
read it line by line
For each line, do a regular expression match (
if ($line =~ /pattern/) ) or use
if (index($line, $searchterm) >= 0) if you are looking for a certain static string.
If you find a match, print the line.
close the file
I hope that gives you enough pointers to get started. You will learn more if you find out how to do each of these steps in Perl by yourself (I pointed out the hard ones).