use strict;
use warnings;

if (@ARGV != 2){# Test for correct number of arguments
  print "This script takes exactly 2 arguments";
  exit;
}

# Open input and output files
open(my $in,  "<", $ARGV[0]) or die "Can't access input file: $!";
open(my $out, ">", $ARGV[1]) or die "Can't write output file: $!";

while (<$in>) {# Loop over the lines of the input file
  if(/text1/i) {# check if line contains "text1"
    s/text1/replaced/gi # replace all instances of "text1" with "replaced"
  }
  print $out $_ # Write the modified line into the output file
}

perl myscript.pl inputfile.txt outputfile.txt

for %f in (*.txt) do perl myscript.pl %f %~nf_out.txt