If (1) the first word of the input line matches the name of a file found in one of the directories listed in the path ($ENV{PATH}), and (2) that file starts with #!/.../perl, and (3) that perl is the same as the Perl under which psh is running, psh will fork and run the script using the already-loaded Perl interpreter. The idea is to save the exec half of the fork-exec that the executable strategy would do; typically the exec is more expensive. Right now this strategy can only handle the -w command-line switch on the #! line. Note this strategy only makes sense before the "executable" strategy; if it came after, it could never trigger.