I have a command
my $output = `somecommand parm1 parm2`;
When I try to run this Perl script I get the message
Can't exec "somecommand" at .....
It seems it is not seeing anything past the first space in between the backticks. I have a friend who runs this in a different environment and it runs fine.
What could I have in my environment that would cause this? I am running Perl v5.20 but so is my friend.
Perl's not ignoring the command parameters, it's just mentioning only the part of the command that it has a problem with -- it can't find somecommand
Whatever your somecommand is, it's not a shell command and it's not in a directory listed in your PATH variable
Change PATH to add its location to the end and it will work for you. You can do that system-wide or you dan modify it temporarily in your Perl code by manipulating $ENV{PATH} before you run the command
Related
Running Lubuntu -
Beginner Perl programmer
Script is XXX.pl located at ~/projects/XXX/XXX.pl
First line is the shebang
#!/usr/bin/perl
Permission to run is set to Anyone.
In directory ~/projects/XXX, the command
~/projects/XXX$ perl XXX.pl
works as desired, but the command
~/projects/XXX$ XXX.pl
Fails with XXX.pl: command not found
What am I missing ?
The two usual options to execute your Perl script are:
perl XXX.pl
or
./XXX.pl
Both ways assume that your current working directory contains the script XXX.pl, otherwise it won't work.
As already pointed out by jm666 in the comments, you can usually not execute a program or script from your current working directory without prepending ./, primarily because of security reasons. Now, you may wonder why it's necessary.
Explanation:
Your shell uses the contents of an environment variable called $PATH to find out about where external commands (non-builtin programs) are located in your filesystem. If you want to see what's in $PATH, just type the following in your shell:
echo $PATH
Now you can see that the $PATH variable does NOT contain your current working directory. The consequence is that your shell is not able to find the program XXX.pl. By prepending ./ you instruct the shell to execute the program which comes after.
But there are two requirements if you want to execute your Perl script with ./script.pl:
The script has to be executable (check with ls -l)
The first line (shebang line) has to be #!/path/to/your/perl because your shell needs that information to find the perl interpreter in order to run your script
However, #1 and #2 are NOT required when you execute your script with
perl XXX.pl
because it invokes the perl interpreter directly with your script.
See how to make Perl scripts executable on Linux and make the script itself directly executable with chmod for some more details.
Can the script be found?
Is . in your path? If it's not, add it to your path, or use ./XXX.pl instead of XXX.pl.
Can the script be executed?
Do you have execute permission to the file? Fix using chmod u+x XXX.pl.
Is the interpreter correct?
which perl will tell you which interpreter is used when you use perl XXX.pl. That's the path that should be on your shebang (#!) line.
I am looking for a nice way to get the following done:
So I have a script that I need to run in Python in Unix by calling from a Perl script that was, in turn, called from my Excel VBA macro in Windows using Plink. The Python script, due to dependency issues, has to run in either csh or bash, and I will need to use export/setenv to add a few libraries before running the script. However by default, perl runs in sh shell and as such, there is no way I can add in all the dependencies and have the Python script to run.
So, I am just wondering if there is EITHER: 1. a way for me to add dependencies to sh shell in the perl script, OR 2. force my perl script to run in csh (preferred, since for some reason .bashrc for the account runs into permission issues).
Thanks a lot!
How about "3. Set the appropriate environment variable in the Perl or Python scripts"?
$ENV{'PATH'} = ...
...
os.environ['PATH'] = os.pathsep.join(newpaths + os.environ['PATH'].split(os.pathsep))
(dunno how to get the path separator in Perl, sorz)
To force the shell to csh, try the following in Perl :
`/bin/csh -c "command_name"`;
Edit:
You can use ENV variable, like this. Try that :
$s = `/bin/bash -c 'VAR_FOO=753; echo \$VAR_FOO'`;
print $s;
I ended up just change the .cshrc script, apparently the addition to PATH, for some reason, did not work for me. After that, everything runs smoothly by putting all into one line
so basically it looks something like this
/path/to/.cshrc && /python/path/to/python
Hope that helps!
I have this perl script that I need to distribute to my coworkers who want to run the script from anywhere in the unix environment. What can I do on my part to make running this PERL script easy for them? For example, they can just have the PERL script somewhere in their directory and run just typing
./xyz.pl ttt.conf
with no path declared (like /home/abc/bin/ddd/xyz.pl ttt.conf).
The way I used to do it is add a "bin" directory in your home directory, and add it to the $PATH variable.. then you can add any script you want to use to that directory.
I am no longer familiar with the exact syntax, but something like:
in .bashrc:
$PATH = ( $PATH , $HOME/bin )
Then place the script in /home/user/bin (assuming $HOME == /home/user). When you reload the shell, it will be usable like any normal command/program.
ETA: See robert's comment below on syntax. Also, to allow your co-workers to use a script of yours, you can simply use a hard-coded path, such as /home/patrick/bin.
Put the script in /usr/local/bin (or anywhere else in $PATH). Your sysadmin may have to help you.
The technique I use is:
#!/usr/bin/env perl
This is a common way of getting the command interpreter to find Perl without either (a) moving the file, or (b) declaring the explicit path for Perl in the shebang.
It's mentioned under portability at: http://en.wikipedia.org/wiki/Shebang_(Unix)
You all are kind of right... but that perl script can sit in your path till the cows come home... and it ain't gonna run... until you set the executable bit....
:bin localadmin$ ./perlextip
-bash: ./perlextip: Permission denied
:bin localadmin$ chmod +x perlextip
:bin localadmin$ ./perlextip
Exit 0! Yeehaw.
Also, it should be noted that it need not be IN your path.... You can just call it by the full path, preceeded with a period and a slash, to execute it..
:/ localadmin$ ./ServiceData/UNIX/bin/extip
Exit 0! Yeehaw.
You can also create an alias for such a command in your ~/.bash_profile, or the such, which will let you make a system-wide shortcut of sorts, and you can even throw in a sudo, or the like, if you were so inclined... Then just call that "extip" by name anywhere, you'll be prompted for a password and, all will be well in the world.
alias extip='sudo ./ServiceData/UNIX/bin/extip'
Maybe it's dumbest question in the world, but I seriously have problems with it and could use help. I am trying to run perl script on linux. It's a simple text editing script, nothing fancy. I googled for it and I found that I had to chmod +x it and then just run myscript.pl in the console. Since it's supposed to modify a text file I did myscript.pl > myfile.txt after chmoding it
But it doesn't work. I get: bash: perl myscript.pl: command not found
Unless myscript.pl is in your path you will need to specify the current directory.
$ ./myscript.pl
You can check if the current directory is in your path with $ echo $PATH. If you're frequently using this script you can put it in the path by moving it to a directory that's part of your path, usually ~/bin.
Or by adding the current directory to the $PATH environment variable. Check the documentation for your shell for instructions.
Can you post the first few lines of your script?
Specifically, if you have #!/usr/bin/perl are there any typos on that line, extra spaces, etc.?
Also do a ls /usr/bin/perl (or whatever is on that line) to make sure it's actually there.
It doesn't look like perl is installed on your Linux machine. Do you get the same thing when you try this: # perl -e 'print "hi";' ?
As Chirael said, it sounds like your shebang line (the directive at the top of the file, that tells the shell how to run the script) is invalid somehow. You can bypass the shebang line entirely by invoking your script as:
perl myscript.pl > myfile.txt
You also don't need to set the script's executable bit, as with this method of invocation, you are only reading the script, not executing it (from the shell's perspective).
According to this thread, it could be from different representation of the new line.
Have you written the script on a windows box and copied over to your linux box?
What is your text editor?
I had the same issue, and traced it to DOS line endings (^M). Running dos2unix on the .pl file fixed the issue.
Please use,
./myperl.pl > outfile.txt
to give the current directory path
thanks
I have a perl script (part of the XMLTV family of "grabbers", specifically tv_grab_oztivo).
I can successfully run it like this:
/sw/bin/perl /path/to/tv_grab_oztivo --output /path/to/tv.xml
I use the full paths to everything to eliminate issues with the Working Directory. Permissions shouldn't be a problem.
So, if I run it from the Terminal (Mac OSX) it works just fine.
But when I set it to run via a cron job, nothing appears to happen at all. No output is created etc.
There isn't anything wrong with the crontab as far as I can see, because if I substitute a helloworld.pl for the actual script, it runs just fine at the right time.
So, what can I do to debug? I can see from looking at %ENV in the two cases that the environment is very different, but what other approaches can I take to debugging? How can I see the output of the cron job, which might be some kind of perl "die" message or "not found" message from the shell or whatever?
Or should I be trying to somehow give the cron version of the command the same environment as when it's running as me?
It's often because you don't get the full environment when running under cron. Best bet is to capture the ouput by using the command:
( /sw/bin/perl /path/to/tv_grab_oztivo ... ) >/tmp/qq 2>&1
and then have a look at /tmp/qq.
If it does turn out to be a missing environment, then you may need to put:
. ~/.profile
or something similar, into the execution chain of your cron job, such as:
( . ~/.profile ; /sw/bin/perl /path/to/tv_grab_oztivo ... ) >/tmp/qq 2>&1
If you're looking at %ENV in the two cases, I'd suggest that, as a first step in your perl script, set %ENV to what it is in a cron job, and then trying to run it from the command line. You may need to exec yourself once for this to take full control:
BEGIN {
if (exists $ENV{something_in_your_env_not_in_cron}) {
%ENV = (...);
exec $^X, $0, #ARGV;
}
}
Now try running it, and seeing if there's anything you can do to debug it (including running under perl -d if required). Most likely, you'll find that you end up adding items back into %ENV one at a time until it magically starts working (LD_LIBRARY_PATH is a good one for this, but ORACLE_HOME or DB2HOME for Oracle or DB2 apps might be good choices, too). Then you can either set the variable in your script, or in the crontab.
I'd run a simple shell script by absolute path from the cron command.
Inside that script, I'd ensure that I trapped stdout and stderr to a known (or knowable) file. I'd also ensure that enough of your environment is set. On Unix, you get almost no environment set at all when you run a command via cron - I'm not sure about MacOS X. The standard culprit for problems is PATH. I have a separate .cronfile that sets my working environment enough that I usually don't have problems - that's an analogue of .profile.
On occasion if you can't figure out what's going wrong with your command line, the simplest way to fix it is to turn the whole thing into a shell script. Ideally you shouldn't have to do this, but it can be the fastest way to solve the problem.
File: /files/cron1.sh
#!/bin/sh
/sw/bin/perl /path/to/tv_grab_oztivo --output /path/to/tv.xml
And then in cron:
/files/cron1.sh
This allows you to test the script independent of cron. Remember though that your login shell runs with different environment variables than cron does.
cron usually captures the output of stdout and stderr and e-mailes any output to the crontab owner.
Did you double check your crontab entry to make sure it's valid and will execute at the right time?
Make sure that the script does not need any environment variables set. Otherwise wrap it in another (bash) script, where you can set the environment variables that the other script expects.