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References quick reference

by tye (Sage)
on Apr 05, 2001 at 02:39 UTC ( #69927=perltutorial: print w/replies, xml ) Need Help??

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  1. or download this
        $scalar        ${$sRef}
        @array         @{$aRef}
    ...
        %hash          %{$hRef}
        $hash{KEY}     ${$hRef}{KEY}
        @hash{@list}   @{$hRef}{@list}
    
  2. or download this
        ${$sRefs[0]}   ${$sRefs{key}}   ${getScalarRef()}
        @{$aRefs[0]}   @{$aRefs{key}}   @{getArrayRef()}
        %{$hRefs[0]}   %{$hRefs{key}}   %{getHashRef()}
        @{ $bool ? \%hash1 : \%hash2 }{qw(some keys)}
    
  3. or download this
        $scalar        $$sRef
        @array         @$aRef
    ...
        %hash          %$hRef
        $hash{KEY}     $$hRef{KEY}
        @hash{@list}   @$hRef{@list}
    
  4. or download this
        $array[0]     ${$aRef}[0]     $aRef->[0]
        $hash{KEY}    ${$hRef}{KEY}   $hRef->{KEY}
    
  5. or download this
        ${$aRef->[0]}[1]    $aRef->[0]->[1]    $aRef->[0][1]
        ${$aRef->[0]}{KEY}  $aRef->[0]->{KEY}  $aRef->[0]{KEY}
        ${$hRef->{KEY}}[1]  $hRef->{KEY}->[1]  $hRef->{KEY}[1]
        ${$hRef->{A}}{B}    $hRef->{A}->{B}    $hRef->{A}{B}
    

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[oiskuu]: glibc getlogin just does ttyname() and falls back on getutline(); it's not security related at all. (reminds me of sendmail and remote finger services of the naive early spam era)
[Corion]: But yes, "who started this process" is interesting information :)
[tye]: no, I really believe that "login user" was added as a fundamental bit of info about each process in order to enhance the usefulness of auditing
[Corion]: Ah - if that information is saved in a file, then you could theoretically spam that file and confuse getlogin(). So, don't use it for authentication :)
[tye]: that is what getlogin() certainly *used* to do. I don't believe that is what it certainly should do.
[davido]: /var/run/utmp is 664 i think.
[tye]: Note that my "man getlogin" says that it uses stdin when it should use /dev/tty (calling a glibc bug). But that does not appear to be the case when I test it. But maybe Perl's getlogin() is not using glibc's getlogin().
[oiskuu]: well, run a strace and see what the getlogin does for you.... As I said. SELinux probably has those security labels. But not regular linux.
[tye]: for example, read https://unix. stackexchange.com/ questions/146138/ loginuid-should-be -allowed-to-change -or-not-mutable-or -not
[tye]: I'm not using SELinux and it certainly appears to disagree with you. shrug

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