perl misc

保护hash数据结构的包：

use Hash::Util qw(lock_keys lock_value lock_hash);

# Do not allow any new keys to be added to our hash.  #Existing keys will remain, and their values can still be modified.

# The hash keys must be locked before locking values.lock_keys(%employee); # We do not allow employees to change their name. lock_value(%employee,"name"); # Lock all the keys and the values in our hash, making it # completely read-only. No keys or values can be changed, # added or deleted. lock_hash(%constants);

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my $year=substr($d,0,4);

my $month=substr($d,4,2);

my $mday=substr($d,6,2); 

my $d_info = strftime("%w %d", 0, 0, 0, $mday , $month - 1, $year - 1900, -1, -1, -1);

这时如果month是以0开头的比如09，通过$month-1后,strftime可以按照期望的work。

但是如果直接写 09 - 1 时，就不work了。

因为09被当成8进制，不被strftime接受了。

这个又一次体现了在perl中context的特性。

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一些one-line command

perl -naF 'next if /^#/; print "$F[3]\n"'

perl -e 'for("MachineB","MachineC","MachineD"){`scp command.pl $_:`; `ssh $_ command.pl`; }'.

ls | perl -e '@a=<>;print $a[rand(@a)]'

perl -pi.bak -e 's/Bill Gates/Microsoft CEO/g; s/CEO/Overlord/g'

perl -n -e 'chomp;print $_,$.%5?":":"\n"' ufile

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perldoc -q/-f str

#帮助查询

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$num = ord($char);

$char = chr($num);

#数字比字符快，有心情可以用用数字代替字符