I have a Perl Module that i created and i want to run one of the subroutine in it on a schedule. I know I can just make a small perl script that calls the subroutine and call it from the crontab but if there is a way to call the subroutine right from the crontab that would be cool!
Is this possible?
You can use Perl's -e switch for executing code from the command line, e.g.
perl -e 'use your_module; your_function()'
Make that even shorter with the -M switch for loading a module:
perl -Myour_module -e 'your_function()'
The perlrun man page is your friend.
You can run the subroutine from the command line using something like
perl -MYour::Module=some,functions,to,import,such,as,foo -e 'foo();'
So you will be able to do the same from the crontab. Note that the cron usually runs with a restricted set of environment variables, so you may need to add a -I/path/to/your/modules option.
If you want a more elegant solution, your module can be configured to detect that it is being run as a script and behave differently in that situation. See this discussion: In Perl, how can I find out if my file is being used as a module or run as a script?
Related
I came across the following example. I tried to google but could not find much so I'm posting this question here.
What is the benefit of executing the perl script like this?
How can we make the shell script work like a "normal" shell script once we are through executing the perl code?
Here's the code:
#!/bin/ksh
#! -*- perl -*-
eval 'exec $PERLLOCATION/bin/perl -x $0 ${1+"$#"} ;'
if 0;
print "hello world\n";
# how can I make it behave like a "normal" shell script from this point onwards? What needs to be done?
# echo "hello world" ### this results in error
This idiom is described in the perlrun documentation.
The -x switch scans the whole file and ignores anything that appears before the first line that begins with #! and also contains the word perl.
It means that your system will run the script with the Perl interpreter whether you invoke the script with perl or with a shell command (sh/bash/ksh/etc.)
That is,
$ perl this_script
and
$ sh this_script
will both run the script with perl.
To address your second question, this idiom has just about nothing to do with combining shell script and Perl script in the same file. There are a few different ways to approach that problem, but maybe the most readable way is to write in shell script, but use the shell's heredoc notation to invoke perl code.
#!/bin/bash
# this is a bash script, but there is some Perl in here too
echo this line is printed from the shell
echo now let\'s run some Perl
perl <<EOF
# this is now perl script until we get to the EOF
print "This line is printed from Perl\n";
EOF
echo now this is from the shell script again
1. If you start a Perl script in the usual way:
#!/usr/bin/perl
print "hello world\n";
the #! line will only work if the Perl interpreter is actually installed under /usr/bin. The perl/ksh bilingual script you show is a tricky kluge to make the script work even if perl is installed somewhere else. For more information, see e.g. this.
2. You can't. When the shell process encounters the exec command, it terminates and hands control over to perl. (Technically, it executes perl in place of the shell, without creating a new process.) The only way to run more shell commands after that would be to launch a new shell.
It's way simpler than what's already been posted.
#!$PERLLOCATION/bin/perl
doesn't work because the shebang (#!) line is interpreted by the kernel (not the shell), and the kernel doesn't do variable interpolation.
The code invokes ksh to expand the environment variable and to launch the specified installation of Perl.
I have perl scripts starting with #!/usr/bin/perl or #!/usr/bin/env perl
First, what does the second version mean?
Second, I use Ubuntu. All the scripts are set as executables. When I try to run a script by simply invoking it's name (e.g. ./script.pl) I get : No such file or directory. when I invoke by perl ./script.pl it runs fine.
Why?
The #!/usr/bin/env perl uses the standard POSIX tool env to work around the "problem" that UNIX doesn't support relative paths in shebang lines (AFAIK). The env tool can be used to start a program (in this case perl) after modifying environment variables. In this case, no variables are modified and env then searches the PATH for Perl and runs it. Thus a script with that particular shebang line will work even when Perl is not installed in /usr/bin but in some other path (which must be in the PATH variable).
Then, you problem with ./script.pl not working: you said it has the executable bit(s) set, like with chmod +x script.pl ? But does it also start with a shebang (#!) line ? That is, the very first two bytes must be #! and it must be followed by a file path (to perl). That is necessary to tell the kernel with which program to run this script. If you have done so, is the path correct ? You want to try the #!/usr/bin/env perl variant ;-)
Using #!/usr/bin/env perl gets around the problem of perl not necessarily being in /usr/bin on every system; it's just there to make the script more portable
On a related note, for your second problem, is there a /usr/bin/perl and/or /usr/bin/env? If not, that would explain why running the scripts directly doesn't work; the shebang isn't handled if you run the script as an argument to perl
I've got a batch script that does some processing and calls some perl scripts.
My question is if there was a way to put the perl code directly into the batch script and have it run both types of scripts.
Active Perl has been doing this for years!
Below is a skeleton. You can only call perl once though. Because passing it the -x switch says that you'll find the perl code embedded in this file, and perl reads down the file until it finds a perl shebang (#!...perl) and starts executing there. Perl will ignore everything past the __END__ and because you told DOS to goto endofperl it won't bother with anything until it gets to the label.
#rem = '--*-Perl-*--
#echo off
perl -x -S %0 %*
goto endofperl
#rem -- BEGIN PERL -- ';
#!d:/Perl/bin/perl.exe -w
#line 10
use strict;
__END__
:endofperl
Yes you can.
In fact this is exactly what the pl2bat tool does: it transforms a perl program into a batch file which embeds the perl program. Have a look to pl2bat.bat itself.
So you can take the .pl, convert it with pl2bat, and then tweak the batch part as you need. The biggest part of the batch code must be put at the end of the file (near the :end_of_perl label) because in the code at the top you are limited to not using single quotes.
However:
this simple approach will not work if you need to embed more that one perl file
this will be a maintenance nightmare.
So I suggest instead to write the whole process in one Perl program.
Update: if you have one script and some Perl modules that you want to combine in a single batch file, you can combine the Perl file using fatpack, and then apply pl2bat on the result.
There is a way to do this, but it wont be pretty. You can echo your perl code into a temp .pl file and then run that file from within your .bat.
How do I run a Perl script on OS X?
You can run your Perl script by invoking the Perl interpreter and giving your file as input:
perl myprogram.pl
The easiest way to run a perl script is with the option:
perl myprogram.pl
However, you may find it more useful to add a shebang line at the top of the perl file.
#!/usr/bin/perl
print "Hello World!\n";
In order to execute this script, you need to add execute permissions to your program. Run:
chmod +x myprogram.pl
Now, in order to run your script, you can simply type:
./myprogram.pl
A good tutorial on Perl in OSX can be found here:
http://www.mactech.com/articles/mactech/Vol.18/18.09/PerlforMacOSX/index.html
A generic documentation on executing Perl code is of course perldoc perlrun.
To answer your question directly:
You can run a perl script on any Unix system by either having the code evaluated and executed from command line:
perl -e 'print "Hello World\n"';
Or you can save your Perl script to a file (customarily having .pl extension, say script1.pl and with the first line being #!/usr/bin/perl) and then you can execute it as any Unix program (after setting proper execute permissions)
/path/to/script/script1.pl
You can also execute a script from a file by running perl interpreter as the command and giving the script as a parameter (in this case execute permissions to the script are not needed):
perl /path/to/script/script1.pl
For some reason the whole directory didn't work for me but I just did
perl ~/Desktop/file.pl
(you could also use any folder that is in your user-folder after the ~/)
I have written a library in Perl that contains a certain function, that returns information about a server as a character string. Can I call this function from a shell directly?
My boss asks "Can you call it from a shell directly for the time being?" Because he said that, I think I should be able to do it, but how do I do it?
perl -MServerlib=server_information -e 'print server_information()'
Is another way to do this, but only if Serverlib exports server_information sub. If it doesn't, you would need to do the below instead:
perl -MServerlib -e 'print MServerlib::server_information()'
As perl's command line arguments are a bit inscrutable, I'd wrap it in a simpler perl script that calls the function. For example, create a script serverinfo which contains:
#!/usr/bin/perl
require 'library.pl';
say library::getServerInformation();
then run:
chmod u+x serverinfo
The advantage of doing it this way is the output and arguments of the script can be corrected if the function itself changes. A command line script like this can be thought of as an API, which shouldn't change when the implementation changes.