Start an MS window in background from a perl script

rlambert7 has asked for the wisdom of the Perl Monks concerning the following question:

I want to start "notepad" in the background from a perl script. On my PC I have both Cygwin and ActivePerl. This is my test script:

system("notepad.exe &")

Actually, I have two scripts. The only difference between the two is the very first line in the script.

The script on Cygwin starts with:

#!/usr/bin/perl

The ActivePerl script starts with:

#!c:/Perl/bin/perl

The Cygwin script does just what I want, it starts a Notepad window, and the script terminates. The ActivePerl script starts a Notepad window, but also brings up a little message window stating that it can't find the file "&.txt", and the perl script is waiting on the Notepad window. Obviously, it "thinks" I am passing the file name "&" as the file to open with Notepad. What's wrong? What do I have to do to make the ActivePerl script open the Notepad window in the background (like it does with the Cygwin Perl script)?

Thanks.

Comment on Start an MS window in background from a perl script

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Re: Start an MS window in background from a perl script by ikegami (Patriarch) on Sep 19, 2007 at 05:56 UTC
`&` is a `sh` thing. The same can be achieved using `start` in `cmd`. Update: Better yet, the Windows-specific `system(1, "...command...");`.	[reply] [d/l] [select]
Re^2: Start an MS window in background from a perl script by syphilis (Archbishop) on Sep 19, 2007 at 14:14 UTC
`&` is a `sh` thing But, in a sense, that's an oversimplification. I mean, if I run (in Cygwin's bash shell): `Rob@desktop2 ~ $ perl -e 'system "notepad &"'` [download] then that works as intended. But if I invoke ActivePerl (in the very same Cygwin shell) by running: `Rob@desktop2 ~ $ /cygdrive/c/_32/ap822/bin/perl -e 'system "notepad &"'` [download] then I get the precise (undesired) behaviour as described by the op - where I get told that &.txt does not exist. Is it simply a case of "ActivePerl always assumes that it's being run in the cmd shell" ? ... or is there a more erudite way of explaining this ? Cheers, Rob	[reply] [d/l] [select]
Re^3: Start an MS window in background from a perl script by ikegami (Patriarch) on Sep 19, 2007 at 14:48 UTC
There's no assumption being made as to which shell launched Perl. As documented, the shell used by `system` is constant. On most platforms, that shell is `/bin/sh` (no matter what the user's login shell is or which process launched `perl`), so `system`'s argument must be a `sh` command. `&` can be used to run a background task in `sh`. On Windows (cygwin aside), that shell is `cmd`, so `system`'s argument must be a `cmd` command. `start` can be used to run a background task in `cmd`.	[reply] [d/l] [select]
Re^2: Start an MS window in background from a perl script by rlambert7 (Acolyte) on Sep 19, 2007 at 17:30 UTC
Thanks everyone for your posts. The suggestion of using 'system(1, "...command...");" worked. THANKS. Interestingly, before I even tried to use "system", I thought there might be more than one parameter I could pass to it, but I couldn't find documentation on it, so please let me ask a couple of questions about Perl documentation. I tried "perldoc system", but it said there was no documentation on "system". Where/how could I find the syntax for "system", and a brief synopis? Also, how can I list all of the functions contained in a Perl module, and how do I find a synopsis and syntax of a specific function within a module? (For example, "perldoc Win32::TestGui" gives me some information, but not all of what I would need to effectively use that module). Thanks, again.	[reply]
Re^3: Start an MS window in background from a perl script by pKai (Priest) on Sep 19, 2007 at 20:49 UTC
To get information on functions from perldoc you use the `-f` switch. So it's `perldoc -f system`	[reply] [d/l] [select]
Re^3: Start an MS window in background from a perl script by ikegami (Patriarch) on Sep 19, 2007 at 17:42 UTC
OS-specific differences are documented in perlport. Your last paragraph is really unrelated. Why don't you start a new SoPW thread?	[reply]
Re: Start an MS window in background from a perl script by andreas1234567 (Vicar) on Sep 19, 2007 at 06:20 UTC
Consider Win32::Process. The synopsis looks very much like your `notepad` example. -- Andreas	[reply] [d/l]
Re: Start an MS window in background from a perl script by pKai (Priest) on Sep 19, 2007 at 10:40 UTC
The ampersand thing (-> put the process into the background) is something specific to nix (so will work under Cygwin), which will not be understood by MSWin. A convenient wrapper around this distinction is the Proc::Background module, which will fork under nix and use Win32::Process under Win, depending on the hosting OS.	[reply]
Re: Start an MS window in background from a perl script by duff (Parson) on Sep 19, 2007 at 14:11 UTC
Similar to the suggestions to use Win32::Process, you may want to look at Win32::Job. duff	[reply]


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