which

#!/usr/bin/env perl
#

use strict;

my ($VERSION) = '1.0.0.0' =~ /([.\d]+)/;

my $opt_a = 0;

if (@ARGV) {
    if ($ARGV [0] eq '-a') {
        $opt_a = 1;
    }
    if ($ARGV [0] eq '--version') {
        $0 =~ s{.*/}{};
        print "$0 (Perl bin utils) $VERSION\n";
        exit;
    }
    if ($ARGV [0] eq '--help') {
        $0 =~ s{.*/}{};
        print <<EOF;
Usage: $0 [OPTION] [COMMAND [COMMAND [COMMAND ... ]]]

For each command, report the full path to this command, if any.

Options:
       --version:  Print version number, then exit.
       --help:     Print usage, then exit.
       --:         Stop parsing options.
EOF
        exit;
    }
    if ($ARGV [0] eq '--') {
        shift;
    }
}

# set up defaults.
my @PATH = ();
my $PATHVAR = 'PATH';
my $path_sep = ':';
my $file_sep = '/';
my @PATHEXT = ();

my $Is_DOSish = ($^O eq 'MSWin32') ||
                ($^O eq 'dos') ||
                ($^O eq 'os2') ;

if ($Is_DOSish) {
    $path_sep = ';';
}
if ($^O eq 'MacOS') {
    $path_sep = '\,';
    $PATHVAR = 'Commands';
    # since $ENV{Commands} contains a trailing ':'
    # we don't need it here:
    $file_sep = '';
}

# Split the path.
if (defined($ENV{$PATHVAR})) {
    @PATH = split /$path_sep/ => $ENV{$PATHVAR};
}
# Add OS dependent elements.
if ($^O eq 'VMS') {
    my $i = 0;
    my $path_element = undef;
    while (defined($path_element = $ENV{"DCL\$PATH;$i"})) {
        push(@PATH, $path_element);
        $i++;
    }
    # PATH may be a search list too
    $i = 0;
    $path_element = undef;
    while (defined($path_element = $ENV{"PATH;$i"})) {
        push(@PATH, $path_element);
        $i++;
    }
    # PATH and DCL$PATH are likely to use native dirspecs.
    $file_sep = '';
}

# trailing file types (NT/VMS)
if (defined($ENV{PATHEXT})) {
    @PATHEXT = split /$path_sep/ => $ENV{PATHEXT};
}
if ($^O eq 'VMS') { @PATHEXT = qw(.exe .com); }

COMMAND:
foreach my $command (@ARGV) {
    if ($^O eq 'VMS') {
        my $symbol = `SHOW SYMBOL $command`; # line feed returned
        if (!$?) {
            print "$symbol";
            next COMMAND unless $opt_a;
        }
    }
    if ($^O eq 'MacOS') {
        my @aliases = split /$path_sep/ => $ENV{Aliases};
        foreach my $alias (@aliases) {
            if (lc($alias) eq lc($command)) {
                # MPW-Perl cannot resolve using `Alias $alias`
                print "Alias $alias\n";
                next COMMAND unless $opt_a;
            }
        }
    }
    foreach my $dir (@PATH) {
        if ($^O eq 'MacOS') {
            if (-e "$dir$file_sep$command") {
                print "$dir$file_sep$command\n";
                next COMMAND unless $opt_a;
            }
        }
        else {
            if (-x "$dir$file_sep$command") {
                print "$dir$file_sep$command\n";
                next COMMAND unless $opt_a;
            }
        }
        if (@PATHEXT) {
            foreach my $ext (@PATHEXT) {
                if (-x "$dir$file_sep$command$ext") {
                    print "$dir$file_sep$command$ext\n";
                    next COMMAND unless $opt_a;
                }
            }
        }
    }
}