LinuxQuestions.org - perl: global replace using hash

The task at hand is to change string1 to string2 in a known list of source files. I've written the perl below to fetch string1 and string2 from a separate file and store them in a hash. The problem is that when I try to make the substitution, the hash values do not seem to match string1 from the source file. (I believe this is the problem since when I hard-code string1 and string2, I get the desired result.) Once changed, the text is written back to the original file, so editing in-place is certainly an option, but the process has to be scripted rather than invoked from a command line.

I've included the lc function when loading the hash, since I know at some point in the future, someone will use a capital letter in a key in the input file, but even without the lc function, the result is the same.

TIA for any assistance.
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#!/usr/bin/perl

use strict ; # enforce good programming rules.
use Cwd ; # include module to allow retrieval of current working directory.

#-------------------------------------------------------------------------------------
# Print begin message.
# ====================

print "Beginning Software Distribution Process: " ; system "date +%Y%m%d-%T" ;
print "\n" ;

#-------------------------------------------------------------------------------------
# Set pkg_name variable.
# ======================

my $dir = getcwd; # get current working directory.
my @dir = split /\//, $dir ; # split full path into directory names and load into array.
$_ = @dir[$#dir] ; # set default variable ( $_ ) to last element of directory array.
s/.tmp$// ; # remove .tmp from default variable.
my $pkg_name = $_ ; # store resulting package name.

print "Package name set to: $pkg_name\n" ;
print "\n" ;

#-------------------------------------------------------------------------------------
# Set directory variables.
# ========================

my $PKG_HOME = $dir ;
print "Package home set to: $PKG_HOME\n" ;
print "\n" ;

#-------------------------------------------------------------------------------------
# Set file variables.
# ===================

my $location = "$PKG_HOME/path.logon" ;
my $file_lst = "$PKG_HOME/objects.lst" ;

#-------------------------------------------------------------------------------------
# Create global variables.
# ========================

my $hash_param ; # individual hash rows.
my $key ; # key for hash_param row.
my $value ; # value for hash_param row.
my $code_module ; # holds name of each code module.

#-------------------------------------------------------------------------------------
# Open parameter file and hash old/new database names, and path to appropriate logon file.
# ========================================================================================

my $success = open FILE_PATH, "<$location" ;
unless ($success) {
&err_open ( $location )
}

while (<FILE_PATH>) {
($key, $value) = split(/:\s*/, $_) ;
chomp ( $key ) ; chomp ( $value ) ;
$hash_param { lc ( $key ) } = $value ;
}

close FILE_PATH ;

#-------------------------------------------------------------------------------------
# Read code module name and call chg_schema subroutine.
# =====================================================

$success = open CODE_MODULE, "<$file_lst" ;
unless ($success) {
&err_open ( $file_lst )
}

while ($code_module = readline CODE_MODULE) {
&chg_schema ( $code_module ) ;
}

close CODE_MODULE ;

exit 0 ;

#-------------------------------------------------------------------------------------
# Subroutine to change code schema.
# =================================

sub chg_schema {

my $file = <$_[0]> ;
print "file: $file\n:" ;
my $success = open FILE_IN, "<$file" ;
unless ($success) {
&err_open ( $file )
}

local $/ ; # enable slurp mode so that entire file is stored in a single variable.

my $lines = lc(<FILE_IN>) ;

print "lines: $lines" ;
close FILE_IN ;

print "old_db: " ; print $hash_param {"old_db"} ; print "\n" ;
print "new_db: " ; print $hash_param {"new_db"} ; print "\n" ;

if (exists $hash_param{"sandbox"}) {
print "old_db value exists\n" ;
} else {
print "no match for old_db\n" ;
}

$success = open ( FILE_OUT , ">$file" ) ;
unless ($success) {
&err_open ( $file )
}

for ( $lines ) {
#$# s/sandbox/production/g ;
s/$hash_param {"old_db"}/$hash_param {"new_db"}/g ; #%#
print FILE_OUT ;
}

close FILE_OUT;
}

#-------------------------------------------------------------------------------------
# Subroutine to process file-open errors.
# =======================================

sub err_open {
system "touch tiv_inst.err" ;
system "date +%Y%m%d-%T" ;
die "File open failure: $_[0]\n$!" ;
}

### File contents listed below; actual files do not include '#' symbol. ###
#-------------------------------------------------------------------------------------
# Contents of path.logon.
# =======================
#old_db: sandbox
#new_db: production
#path: /home/ken/chek

#-------------------------------------------------------------------------------------
# Contents of objects.lst.
# ========================
#test1.vew

#-------------------------------------------------------------------------------------
# Contents of test1.vew.
# ======================
#replace view sandboxv.test1 as
#select * from sandboxt.event;