I have written a script using perl comnsole Term::ReadLine::Gnu.
How can I run while I'm in the console external commands in the background?
I've managed to support various external commands such as ls -l etc. but I also wish to support running commands in the background such as emacs &, but I can't seem to be able to get a process to run in the background.
Is there a solution?
To execute something in the background, you can use system:
#!/usr/bin/env perl
use strict;
use warnings;
system q(emacs &);
print "hello";
This will open emacs in the background and print "hello" straight away. If you removed the & in the command it would wait for emacs to close before printing "hello".
As pointed out by #Brad in the comments, note that this will only work on systems where the shell understands the &. If you were running on Windows for example, you would have to change the system line to something like this:
system q(start /b program.exe);
See the system documentation for more details.
Related
I'm new to mojolicious but have been using Perl for some time. I have to jump through some hoops but I can get the interactive Perl debugger (and Komodo) working with remote connections for Apache but I can't find anything about interactive debugging with hypnotoad or morbo.
The command line examples in the basic tutorial on http://mojolicio.us/perldoc/Mojolicious/Guides/Tutorial#Hello-World work fine because you can launch them with perl -d, but I don't see anyway to tell the hypnotoadctl script to put the service in interactive debug mode ala apache.
Is this not possible? Hints? Tips? Pointers?
morbo and hypnotoad are perl programs, so you can launch them with the -d switch.
perl -d $(which morbo) myMojoApp.pl
It's probably easiest to sprinkle a bunch of $DB::single = 1 statements around you app where you want your initial breakpoints to go and run c as the first debugger command. When you run a request that hits a breakpoint, you'll get a debugger prompt in the terminal that launched morbo.
hypnotoad will be trickier to use with the debugger because it quickly closes all the standard filehandles, calls fork several times, and becomes a daemon.
As JHThorsen points out, standard Mojolicious tests are actually ordinary Perl scripts, so you can debug your tests with:
perl -d t/mytest.t
The -Ilib adds the lib/ directory to the #INC include list so your modules will be loaded.
One catch is that many modules are not loaded until execution time, so if the debugger hassles you about symbols that aren't loaded yet, you'll probably want to set breakpoints after forcing a debug prompt with a carefully inserted
$DB::single = 1;
Thanks to 'pink_mist'. You can do:
perl -d myMojoApp.pl daemon -l http://*:29849
But application config is not applyied. I do not know why.
I can use system in Perl 5 to run external programs. I like to think of system like a miniature "Linux command line" inside Perl. However, I cannot find documentation for system in Perl 6. What is the equivalent?
Perl6 actually has two commands that replace system from Perl 5.
In Perl6, shell passes its argument to the shell, similar to Perl 5's system when it has one argument that contains metacharacters.
In Perl6, run tries to avoid using the shell. It takes its first argument as a command and the remaining arguments as arguments to that command, similar to Perl 5's system when it has multiple arguments.
For example:
shell('ls > file.log.txt'); # Capture output from ls (shell does all the parsing, etc)
run('ls','-l','-r','-t'); # Run ls with -l, -r, and -t flags
run('ls','-lrt'); # Ditto
See also this 2014 Perl 6 Advent post on "running external programs".
In addition to using shell or run, which replace system from Perl 5, you can also use NativeCall to invoke the libc system function.
On my Windows box, it looks like this:
use NativeCall;
sub system(Str --> int32) is native("msvcr110.dll") { * };
system("echo 42");
How would I determine what script, program, or shell executed my Perl script?
Example: I might want to have human readable output if executed from shell (customized for each type of shell), a different type of output if called as a script from another perl script, and a machine readable format if executed from a program such as a continuous integration server.
Motivation: I have a tool that changes its output based on which shell executes it. I'd normally implement this behavior as an option to the script, but this tool's design doesn't allow for options. Other shells have environment variables that indicate what shell is running. I'm working on a patch to support Powershell, which has no such special variable.
Edit: Many of these answers happen to be linux specific. Unfortuantely, Powershell is for Windows. getppid, the $ENV{SHELL} variable, and shelling out to ps won't help in this case. This script needs to run cross-platform.
You use getppid(). Take this snippet in child.pl:
my $ppid = getppid();
system("ps --no-headers $ppid");
If you run it from the command line, system will show bash or similar (among other things). Execute it with system("perl child.pl"); in another script, e.g. parent.pl, and you will see that perl parent.pl executed it.
To capture just the name of the process with arguments (thanks to ikegami for the correct ps syntax):
my $ppid = getppid();
my $ps = `ps --no-headers -o cmd $ppid`;
chomp $ps;
EDIT: An alternative to this approach, might be to create soft links to your script, make the different contexts use different links to access your script and inspect $0 to build logic around that.
I would suggest a different approach to accomplish your goal. Instead of guessing at the context, make it more explicit. Each use case is wholly separate, so have three different interfaces.
A function which can be called inside a Perl program. This would likely return a Perl data structure. This is far easier, faster and more reliable than parsing script output. It would also serve as the basis for the scripts.
A script which outputs for the current shell. It can look at $ENV{SHELL} to discover what shell is running. For bonus points, provide a switch to explicitly override.
A script which can be called inside a non-Perl program, such as your continuous integration server, and issue machine readable output. XML and/or JSON or whatever.
2 and 3 would be just thin wrappers to format the data coming out of 1.
Each is tailored to fit its specific need. Each will work without heuristics. Each will be far simpler than trying to guess the context and what the user wants.
If you can't separate 2 and 3, have the continuous integration server set an environment variable and look for it.
Depending on your environment, you may be able to pick it up from the environment variables. Consider the following code:
/usr/bin/perl -MData::Dumper -e 'print Dumper(\%ENV);' | grep sh
On my Ubuntu system, it gets me:
'SHELL' => '/bin/bash',
So I guess that says I'm running perl from a bash shell. If you use something else, the SHELL variable may give you a hint.
But let's say you know you're in bash, but perl is run from a subshell. Then try:
/bin/sh -c "/usr/bin/perl -MData::Dumper -e 'print Dumper(\%ENV);'" | grep sh
You will find:
'_' => '/bin/sh',
'SHELL' => '/bin/bash',
So the shell is still bash, but bash has a variable $_ which also show the absolute filename of the shell or script being executed, which may also give a valuable hint. Similarily, for other environments there will most probably be clues left in the perl %ENV hash that should give you valuable hints.
If you're running PowerShell 2.0 or above (most likely), you can infer the shell as a parent process by examining the environment variable %psmodulepath%. By default, it points to the system modules under %windir%\system32\windowspowershell\v1.0\modules; this is what you would see if you examine the variable from cmd.exe.
However, when PowerShell starts up, it prepends the user's default module search path to this environment variable which looks like: %userprofile%\documents\windowspowershell\modules. This is inherited by child processes. So, your logic would be to test if %psmodulepath% starts with %userprofile% to detect powershell 2.0 or higher. This won't work in PowerShell 1.0 because it does not support modules.
This is on Windows XP with PowerShell v2.0, so take it with a grain of salt.
In a cmd.exe shell, I get:
PSModulePath=C:\WINDOWS\system32\WindowsPowerShell\v1.0\Modules\
whereas in the PowerShell console window, I get:
PSModulePath=E:\Home\user\WindowsPowerShell\Modules;C:\WINDOWS\system32\WindowsP
owerShell\v1.0\Modules\
where E:\Home\user is where my "My Documents" folder is. So, one heuristic may be to check if PSModulePath contains a user dependent path.
In addition, in a console window, I get:
!::=::\
in the environment. From the PowerShell ISE, I get:
!::=::\
!C:=C:\Documents and Settings\user
Seems most are using the traditional way of print for debugging purpose, is there anyone that uses remote debug for perl in linux?
There are reasonably straightforward directions here: http://search.cpan.org/dist/Enbugger/lib/Enbugger.pod#From_gdb
Though that presupposes you have a long-running perl process (mod_perl, fastcgi, etc) that wasn't expecting to be run under the debugger. If you are just using vanilla CGI, you can configure your webserver to run perl -d and set the debugger to remote debugging via its TTY or RemotePort options. Or go ahead and use Enbugger in your actual perl code as in the directions above (again, setting TTY or RemotePort).
What sort of debugging? An actual perl debugger or using warn() with tail -f /var/log/apache/error.log?
In the end i would suggest swicting to Log::Log4perl. Unless you need an actual step by step debugger.
You you need an actual debugger, you likely won't want to use Apache in the mix. You can run your cgi from the command line and pass arguments CGI.pm.
I have this command that I load (example.sh) works well in the unix command line.
However, if I execute it in Perl using the system or ` syntax, it doesn't work.
I am guessing certain settings like environment variables and other external sh files weren't loaded.
Is there an example coding to ensure it will work?
More Updates on coding execution failure (I have been trying with different codes):
push (#JOBSTORUN, "cd $a/$b/$c/$d; loadproject cats; sleep 60;");
...
my $pm = new Parallel::ForkManager(3);
foreach my $job (#JOBSTORUN) {
$pm->start and next;
print(`$job`);
$pm->finish;
}
print "\n\n[DONE] FINISHED EXECUTING JOBS\n";
Output Messages:
sh: loadproject: command not found
Can you show us what you have tried so far? How are you running this program?
My first suspicion wouldn't be the environment if you are running it from a login shell. any Perl script you start (well, any program, really) inherits the same environment. However, if you are running the program through cron, then that's a different story.
The other mistakes I usually make in these situations is specifying the relative paths incorrectly. The paths are fine from the command line, but my Perl script has some other current working directory.
For general advice, see Interact with the system when Perl isn't enough. There's also a chapter in Learning Perl about this.
That's about the best advice you can hope for given the very limited information you've shared with us.