perl -p -i.bak -e 's/\$Log/\$History/gi' *
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Creates backupfiles with the extension .ext and modifies the original files where all occurances of $Log are replaced with $History. This is done for every file in this case since you choice *.

 $InputArray is a scalar not an Array.
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To replace any occurance of $Log to $History: try this but on a backup please. the first argument is the dir where the files life.

#!/usr/bin/perl
use File::Find;
my @dirs = @ARGV;
@ARGV = ();
File::Find::find(
  {
    wanted => sub { push @ARGV, $File::Find::name if -f }
  },
  @dirs
);
local $^I;
while ( defined( $_ = <ARGV> ) ) {
  s/\$Log:/\$History:/gi;
  print;
}
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