system("foo.pl","&");

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This calls foo.pl with the character & as its first argument. 

system("foo.pl  & ");

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This calls /bin/sh (or your appropriate system shell) and passes it the whole string as command. The shell then interprets the & as a directive to background the command.

The next two are equivalent, but only in the second the shell is involved: 

system("foo.pl", "&");
system("foo.pl '&' ");

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In reply to Re: system function behaviour by shmem
in thread system function behaviour by dharanivasan

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