As system always starts a new shell (or no shell at all, in case the command doesn't contain any shell metacharacters), the only way to make shell functions available is by sourcing the definitions in that new shell.  And in case you need a ksh, you'll also want to start the shell yourself: 

system('/bin/ksh', '-c', '. /env.ksh ; shellFunction');

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Or, in case env.ksh is huge, and you want to avoid re-sourcing it every time, you could open a pipe to the shell, e.g. 

my $pid = open my $shell, "| /bin/ksh" or die "Couldn't start ksh: $!"
+;
print $shell ". /env.ksh\n";

print $shell "shellFunction\n";

# later
print $shell "shellFunction2\n";
# ...

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In reply to Re: shell within system() call by almut
in thread shell within system() call by claudius

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