Please add use strict; to the top of your program. Then Perl will tell you what happens:

Global symbol "$JAVA_HOME" requires explicit package name at 564926.pl
+ line 4.
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Perl sees the variable $JAVA_HOME and replaces it with its value, which is empty. The strict pragma prevents you from inventing variables.

If all you want to do is get at the value of environment variables, these are all available in the %ENV hash:

my $res = $ENV{JAVA_HOME};
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If you want to know how to pass strings that look like variable names to the shell via backticks, you need to quote the special chars:

my $res = `echo \$JAVA_HOME`;
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If you want to know how to pass strings that look like variable names to the shell via backticks, you need to quote the special chars:

my $res = `echo \$JAVA_HOME`;
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To be completely thorough and pedantic, you can also use the qx operator with single quotes:

my $res = qx'echo $JAVA_HOME';
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-QM
--
Quantum Mechanics: The dreams stuff is made of

Your mistake is that perl interpolates $JAVA_HOME before the echo command is executed and I guess $JAVA_HOME in your code isn't defined.

Try $ENV{JAVA_HOME} to get the variable you want.

If you insist (for any reason) to use the echo command's output or need to bypass the perl interpolation, write \$JAVA_HOME.

Enjoy,
Mickey

Update: mickeyn found the problem.