Article 6978 of comp.lang.perl:

Article 6978 of comp.lang.perl:
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From: Tom Christiansen <[email protected]>
Subject: Re: How to determine whether running Perl 4 or perl 5?
Message-ID: <[email protected]>
Originator: [email protected]
Sender: [email protected] (USENET News System)
Reply-To: [email protected] (Tom Christiansen)
Organization: University of Colorado, Boulder
References: <[email protected]>
Date: Tue, 19 Oct 1993 11:44:20 GMT
Lines: 119

From the keyboard of [email protected] (Stephen O. Lidie):
:Can a Perl program determine at run time whether Perl 4 or Perl 5 is in
:control?

Of course you can use $], although for really old versions,
you must use it as a string and not a number. The problem is
that perl4 probably won't compile perl5 code at all, so you won't
get that far.

To deal with this, I have on occasion used this. It has its limits.
I may make it better and take a path of directories.

#!/usr/local/bin/perl
#
# preambulate -- wrap a perl program with a system-independent preamble.
#
# Tom Christiansen [email protected]

$mypath = '/usr/local/bin/perl';
($myversion, $mypatchlevel) = $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;

unless (@ARGV) {
unshift(@ARGV, '-');
$was_stdin++;
}

while ($file = shift) {
open(file, $file) || die "can't open $file: $!";
$mode = (stat(file))[2] & 0777;
if ($file ne '-') {
$TMP = "$file.tmp";
open (TMP, ">$TMP") || die "can't create $TMP: $!";
} else {
open (TMP, ">&STDOUT");
}
print TMP <<'EOF';
#!/bin/sh -- need to mention perl here to avoid recursion

'true' || eval 'exec perl -S $0 $argv:q';
eval '(exit $?0)' && eval 'exec perl -S $0 ${1+"$@"}'
& eval 'exec perl -S $0 $argv:q'
if 0;

VERSION_SANITY: {
package VERSION_SANITY;
local($_);
EOF
print TMP <<"EOF";
\$PERL_PATH = '$mypath';
local(\$version, \$patchlevel) = ($myversion, $mypatchlevel);
EOF

print TMP <<'EOF';

local($want_vp) = sprintf("%d.%03d", $version, $patchlevel);
local($need_perl) = $PERL_PATH . $want_vp;

die "can't get version"
unless $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;

sub try_version {
warn "current perl version ($got_vp) too low, execing $need_perl\n";
exec $need_perl, $0, @ARGV;
warn "exec of $need_perl failed: $!";
}

if ($1 < $version || $2 < $patchlevel) {
local($got_vp) = sprintf("%d.%03d", $1, $2);
&try_version if -x $need_perl;
for $need_perl (reverse sort </usr/local/bin/perl* /usr/bin/perl*>) {
next unless $need_perl =~ /perl(\d+)\.(\d+)$/;
&try_version if $1 >= $version && $2 >= $patchlevel;
}
warn "WARNING: perl version too low: $got_vp < $want_vp; good luck...\n";
}
}

@VS'info = (__FILE__, __LINE__); eval <<'___VERSION_SANITY___';

# BEGIN REAL PROGRAM

EOF

while (<file>) {
print TMP;
}

print TMP <<'EOF';

# END REAL PROGRAM

___VERSION_SANITY___

if ($@) {
$_ = $@;
($file, $line) = @VS'info;
s/ file $eval$ at line (\d+)/" $file at line " . ($1 + $line)/eg;
s/ at $eval$ line (\d+)/" in $file at line " . ($1 + $line)/eg;
die $_;;
}

exit 0;

EOF

unless ($file eq '-') {
close TMP;
chmod $mode, $TMP;
rename ($file, "$file.bak") || die "can't rename $file to $file.bak: $!";
rename ($TMP, $file) || die "can't rename $TMP to $file: $!";
}
}
--
Tom Christiansen [email protected]
"Will Hack Perl for Fine Food and Fun"
Boulder Colorado 303-444-3212