The problem is that in case if $string contains characters like $ or @ or % then these values are getting replaced by the perl keys.

"Interpolation", as it's called, goes only one level deep. Hence, it's the string contents of the variable $string that is inserted in the command line. Contrary to what you seem to believe, nothing else is replaced.

And %hash is never interpolated in a string. Never.

What may happen is that the invoked shell may treat shell metacharacters in this command line special (for example, replace parts of the command line by environment variables). But that's not Perl's fault. That's why $d may appear to disappear from your command line.

Use of String::ShellQuote may help you in alleviating that problem.

Alternately use the LIST form of system yourself directly (or IPC::Run if you need the output from the subprocess) and take any intermediary shell out of the picture to begin with and you won't need to worry about quoting.

my $test_sh_ret = system( "test.sh", $string );
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bart is correct, but special shell quoting modules may be overkill. I think you can probably get away with the multi argument version of system iff you don't need the output to come back from the qx.

You can also open my $in, "-|", qw(program), "$sting" or die $! to get the output and use the multi-arg pipe. Huzzah.

...

my $PATH = "!please don't show this!";

my $command = 'echo test.sh';
my $args    = "\\\$PATH is a name";     # try: "\$PATH is a name";

print "args: ",  $args, "\n";
print "dummy: ", $PATH,"\n";

my $output = qx{ $command $args };      # use qx for backticks!
print "\ncommand line echo: ", $output, "\n";
...
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$ ls
hello
$ perl -e 'my $dir = q(not$socooldir); system "mkdir $dir" and die "ex
+ecution failed\n"'
$ ls
hello  not
$ perl -e 'my $dir = q(not$socooldir); $dir = quotemeta $dir; system "
+mkdir $dir" and die "execution failed\n"'
$ ls
hello  not  not$socooldir
$ perl -e 'my $dir = q(not$socooldir); system "mkdir \Q$dir" and die "
+execution failed\n"'
mkdir: cannot create directory `not$socooldir': File exists
execution failed
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Of course, perl has its own mkdir function, internally. Please note that the third execution fails because directory already exists, indicating that \Q$dir and quotemeta $dir result in the same directory name.

One more thing, please don't use `shellcmd args` in void context, because you ask for something to return but effectively discard it. Assign it to a scalar or an array to capture the output if you want it so.

my @lines = `shellcmd args`; # list context
my $line = `shellcmd args`; # scalar context
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