I mean open does not detect error if you "open" a directory.

Sure it does 

$ perl -e " open $dirname, q/../ or die $!, $/, $^E, $/ "
Permission denied
Access is denied

$ perl -e " open $dirname, q/../ or die join qq/\n/, $!,$^E,grep( { $!
+{$_} } keys %! ) "
Permission denied
Access is denied
ERROR_INVALID_DATA
EMARCH_ENC_I17_IMM5C_INST_WORD_POS_X
EMR_SETBRUSHORGEX
EVENT_SYSTEM_CONTEXTHELPEND
EACCES at -e line 1.

[download]

Also last code with "wantarray" and "scalar" looks useless.

No, its is not useless. You must not know perl well.

In reply to Re^6: Wrong idioms (open $fh, '<', undef) by Anonymous Monk
in thread Wrong idioms by McA

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