I often combine Unix's find-exec and perl-pie like this:

$ find /path/to/files -name "*.xml" -exec perl -p -i -e 's/this/that/g
+' {} \;
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Depending on the snippet/string/filename relationship, you may be able to repeat the above, just changing find's -name and perl's "this" and "that":

$ find /path/to/files -name "*.txt" -exec -perl -p -i -e 's/these/thos
+e/i' {} \;
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Or you can create a simple perl or other script and use find to pass in the filename:

$ find /path/to/files -type f -exec changeIt.pl {} \;
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However, as this is a professional application, it is important that it be provably correct. Like most people, I, and I suspect you, learn by making mistakes. Given the possibly intense time pressure you are under, do you want to wind up doing your 'learning' in front of your boss? It might be safer to 'just do it' in a language you know, i.e., C or C++, and learn Perl at a more leisurely pace in preparation for the next rush assignment.

Here's some example code snippets. Hopefully it will help narrow down what you need to focus on for this project.

# start your program with these. trust me
use strict;
use warnings;


# hash table of search strings and insertion code
my %insertions = (
    'search string' => 'code insertion',
    foo => 'bar',
    alpha => 'beta',
);


# read in array of filenames from a directory
opendir (my $DH, $directory);
my @files = $readdir $DH;
closedir $DH;


# iterate over array of filenames
for my $filename (@files){
    
    # process your file here
    # or use a subroutine
    subName($filename);
}


# basic subroutine
sub subName{

    # get first arg passed
    my $filename = shift;

    # if you need a return value
    return $foo;
}


# opening files. $TFH = target filehandle
open (my $TFH, ">", $targetfile);
open (my $SFH, "<", $sourcefile);

# read source file line by line
while (my $line = <$SFH>){ 
    print $TFH, $line;

    # use regular expression to find matching string 
    if ($line =~ /$matchString/){   
        print $TFH, $snippet;
    }
}
close $TFH;
close $SFH;
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This is precisely how I started using perl - making small and huge changes to hundreds or thousands of files simultaneously (which then made me think about how to make it such that such silliness wasn't repeated in so many files in case it changed again - which it has). I knew sed and awk, but they got far too convoluted far too quickly. I started with perlintro and went from there. Coming from C++, you should have no problem (which is my background as well, though I had been doing some shell scripting, too).