As moritz said, this is actually a shell command. eval is both a shell and a Perl command, but in this case it is the shell version.

In most UNIX shells (not csh), $? is the status of the previous command (in Perl it is the exit status of the previous child process - not the same thing). In a shell, parentheses create a sub-shell which is a new shell environment (I use the term loosly) in the same process, so eval '(exit $?0)' in shell exits the sub-shell (not the current process). In shells, an evaluation of non-zero is considered false, and 0 is considered true (consider 0 to be 'success').

exec also is in both shells and Perl, and it replaces the current program with a new one in the same process, so it will replace the shell with perl.

In this case, the if 0 will be considered part of the command by a shell. However, in Perl the if 0 has precedence, so none of that will be executed if we are running perl, zero being false in perl (and most languages). Try:
print "A " && print "B " && print "C " if 0;

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In reply to Re: What is the intention and logic of this line in the beginning of the script? by cdarke
in thread What is the intention and logic of this line in the beginning of the script? by accessdenied

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