On 2024-07-19 at 09:02, Michel Verdier wrote:
> On 2024-07-19, p...@gmx.it wrote:
>
>> $ perl -le 'for( keys %ENV ){print "$_ --> $ENV{$_}"}' |grep perl
>> _ --> /usr/bin/perl
>>
>> the key for perl is "_" in environment variable? under this key, why
>> 'env perl' just works?
>
> Perl $_ is the current (unnamed) value of your loop "for". You could
> write it like this:
> foreach my $key (keys %ENV) { print "$key=$ENV{$key}" }
>
> https://perldoc.perl.org/variablesI think the question was not about the '$_' variable in the perl expression, but about the '_' variable in the output, which in this case contains the full path to the 'perl' binary. $ env | grep ^_ _=/usr/bin/env That appears to be a (shell?) environment variable. Greg commented on it, as being a weird thing that you will probably never need to worry about. I have done some experimenting with it, and it appears to hold the equivalent of argv[0] for the command line which invoked the current process - but the logic for determining what that is may well not be intuitive for many people. 'echo $_' produces the full path to 'echo'. 'sh /tmp/testme' (where that file is a '#!/bin/sh' script which runs 'echo $_') produces the full path to 'sh'. 'bash /tmp/testme' (with the script shebang line still pointing to /bin/sh) produces the full path to 'bash'. 'chmod +x /tmp/testme' followed by '/tmp/testme' produces '/tmp/testme'. All in all, I think I agree with Greg's description. -- The Wanderer The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. -- George Bernard Shaw
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