Set environment variable for one time system command windows

rmahin has asked for the wisdom of the Perl Monks concerning the following question:

Hi all, have a question that I hope is easy to answer.

I have multi-threaded server application that needs to set an environment variable, and then execute a command, but not set it for the rest of the threads. Here is an example that shows something similar to what I am doing,

use strict;
use warnings;

if($^O =~ /mswin32/i){
    system("set test=hello && echo %test%");
}else{
    system("test=hello; export test; echo \$test");
}
[download]

The unix portion of the code works flawlessly, the windows portion however just outputs '%test%'. I have tried using ';' and '&' in addition to the '&&' all with no success. is there a way to accomplish what I'm trying to do?

Thanks.

Comment on Set environment variable for one time system command windows Download Code

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Re: Set environment variable for one time system command windows by BrowserUk (Patriarch) on Mar 27, 2013 at 19:10 UTC
The problem is that the variable substitution %test% is done before the command is executed. Ie. the variable in the echo is expanded before the set is exectuted. However, if the second command is an executable rather than a built-in command, the variable is set when the executable runs: `C:\test>set test= & perl -E"system q[set test=fred & perl -E\"say $ENV +{test}\"]" fred` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^2: Set environment variable for one time system command windows by rmahin (Scribe) on Mar 27, 2013 at 19:57 UTC
Well damn haha, just assumed that since the echo wasn't working the variable was not getting set. Thanks for clarifying.	[reply]
Re: Set environment variable for one time system command windows by samwyse (Scribe) on Mar 27, 2013 at 19:55 UTC
In both branches of your if statement, your string contains meta-characters, but on unix the shell expands environment variables as each statement is executed, while on windows they are only expanded once when the line is read. On my windows server, this is what happens when I run your command: `R:\>set test=hello && echo %test% %test%` [download] I need to invoke the shell once more to make it work. `R:\>set test=hello && cmd /c "echo %test%" hello` [download] This should work: `use strict; use warnings; if($^O =~ /mswin32/i){ system(qq!set test=hello && cmd /c "echo %test%"!); }else{ system("test=hello; export test; echo \$test"); }` [download]	[reply] [d/l] [select]
Re^2: Set environment variable for one time system command windows by rmahin (Scribe) on Mar 27, 2013 at 19:59 UTC
This is basically what BrowserUK said as well, thanks for the extra verification	[reply]
Re: Set environment variable for one time system command windows by aitap (Curate) on Mar 27, 2013 at 19:41 UTC
Since running a command requires a separate process, fork it and set the environment variable via %ENV, then exec your program: `if (fork == 0) { local $ENV{myvariable} = "test"; exec("echo ".($^O eq "MSWin32" ? "%myvariable%" : '$myvariable')) or +die "exec: $!\n"; } __END__ text` [download] Sorry if my advice was wrong.	[reply] [d/l]


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