One way is to use the core Config module and calculate the limits from the byte size:

    #!/usr/bin/perl -wl

    use Config;

    print $Config{intsize};
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Another way, as you guessed, is with POSIX:

    use POSIX;

    print POSIX::INT_MAX; 
    print POSIX::INT_MIN; 
    print POSIX::UINT_MAX;
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Or perhaps even this:

    print 0.5 * (-1 + unpack "I", pack "I", -1);
    print 0.5 * (-1 - unpack "I", pack "I", -1);
    print             unpack "I", pack "I", -1 ;
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--
John.