I want to use system commands like mkdir and rmdir while running a java program.
How can I do that?
Why do you want to use the command line? FYI, there are built-in platform-independent File classes.
http://www.exampledepot.com/egs/java.io/deletefile.html
http://www.roseindia.net/java/beginners/java-create-directory.shtml
Make directory:
new File("dir path").mkdir();
Remove directory:
new File("dir path").delete();
'new File' here is a bit of a misnomer, it isn't actually creating the directory or a file. It's creating a Java resource hook which you can use to query or operate upon an existing filesystem resource, or create a new one at your request. Otherwise, use Runtime.getRuntime().exec("command line here") for using command line operations (not advised!!).
Edit: sorted out the problem the question poster was having:
String envp[] = new String[1];
envp[0] = "PATH=" + System.getProperty("java.library.path");
Runtime.getRuntime().exec("command line here", envp);
Note the insertion of envp into the exec(..) method call, which is basically the PATH variable from the environment.
As the other mentioned, you shouldn't do this for simple file management. But to have it mentioned: The Java API has a class called Runtime, that allows system calls... for example:
Runtime.getRuntime().exec("some_command");
The best is not to, but rather find the pure Java API function that does it. It is cleaner, easier to understand and much less error prone. It is also the only way to do Java that is write once run everywhere. Once you are calling shell commands, you are tied to that shell.
In your case you are looking for the java.io.File class, and specifically the mkdir and delete methods.
For reference of people stumbling onto this question and wondering why Runtime.getRuntime().exec("mkdir foo") doesn't work even when incorporating the environment as per Chris Dennett's answer, the most probable reason is that you don't have a program called "mkdir" on your system. While most Unix-like systems have a program of this name, it isn't absolutely necessary for them to have one, and Windows doesn't have one, because in both cases the shell interprets this command itself, rather than passing it to an external program.
To make it work, try ...exec ("cmd /c mkdir foo") for NT-family Windows (or "command /c mkdir foo" for Windows 95 family), or exec ("sh -c \"mkdir foo\"") for Unix.
The fact that there isn't a platform-independent way to do this is yet another reason to prefer the Java APIs for performing the task.
Hi Agree to the fact of not been platform independent but just for testing an app I had to use it.
The solution in my case for the
Runtime.getRuntime().exec("my_command_name") ;
for not working was i had to give the full path to where the batch/sh/executable file was
ie:
Runtime.getRuntime().exec("/d/temp/bin/mybatfile");
Related
I am a high school student working on a project that will convert the video from a YouTube link into an MP3 and download it. However, the way that the video form YouTube is downloaded and converted is through the Mac OS terminal by using YouTube-dl.
This is what I put into the terminal:
youtube-dl -f bestvideo+bestaudio \"ytsearch:{https://www.youtube.com/watch?v=5X-Mrc2l1d0}\"
This works in terminal, but when I try to use:
Runtime.getRuntime().exec("cd /Users/poppa/Desktop/IA Vids");
and there's an error saying "No such file or directory"
Another Problem that I am having is running the code that is inputted into the Terminal from Java. I'm using IntelliJ IDEA if that helps. Thank You!
You have a space in the directory path. Try putting double quotes around like this:
Runtime.getRuntime().exec("cd \"/Users/zeidakel/Desktop/IA Vids\"");
Also note that executing cd command from JVM may have no effect on current user dir when (for example) creating files with new File("path")
If cd means change directory (and isn't the name of an executable), then it almost certainly won't take effect, even if it is executed correctly. The process spawned by exec() will have a working directory, and it can be changed -- but that change will only affect the spawned process.
In addition, having spaces in arguments to exec() is inherently problematic. exec() is not a shell, and you won't be able to protect the string from being split at the spaces by using shell mechanisms like quotes. Instead, you need to split the command into arguments yourself, knowing where the splits should be, and then use the form of exec() that takes a String[] as input. That is, split the arguments into an array of strings yourself, rather than relying on exec() to do it for you (wrongly).
Runtime.exec() is fraught with difficulties, and needs very careful handling. I've written extensively about this subject here:
http://kevinboone.me/exec.html
I am interested in executing the cmd.exe move command from a Java application.
I know how to invoke external processes from within Java. There are 100's of questions on this point in StackOverflow. What I can't figure out, is what the command line should look like.
For example, in a DOS window, this is the command I type:
move dirA dirB
and the directory dirA is moved to directory dirB. Exactly what I want done. For reasons that require far too much context, and will detract from the question, a pure java solution is not an option in the specific context I am concerned with. (Oh the joys of operating in an enormous and complex legacy systems!)
What is the external system command I invoke from java to do that? It seems like it should just be:
"cmd move dirA dirB"
However, that fails for me. I am familiar with this question, but it does not directly answer my question.
No guarantees but I suppose, that you need to prepend the command to run the Windows command shell cmd /c to the command you want to execute. The /c switch terminates the command shell after the desired command completes.
Try:
Runtime.getRuntime().exec("cmd /c move dirA dirB");
EDIT:
As Ian Roberts
have noticed in his comment below, it is also important to take into consideration situation when one or both of directories have spaces in their paths. It is thus much safer to use separate strings to form the finall command, i.e like below:
new ProcessBuilder("cmd", "/c", "move", pathToDirA, pathToDirB).start()
I want to create a folder that starts with . character. I tried File(path).mkdir() but does not work. I cannot create from "right click->new folder". Windows blocks creating folders starting with dot character. From command prompt I can easily create via mkdir [folder_name]. Do I have any mistakes here. If not how can I execute this command in java or any other suggestion will be helpful?
Note: Process p = Runtime.getRuntime().exec("mkdir .test"); //Does not work
Note2: My code will be platform dependent.
new File("C:\\Temp\\.folder").mkdir();
Works for me. Note that mkdir() returns a boolean which indicates success or failure. It can fail if you have no permission to create the folder, for example.
(Note: When you ask a question, explain what "does not work" means.)
Platform independant OS functions are not so simple in java but you could wrap it around an ant mkdir task that would be platform independant. The usage is slightly roundabout but is/could be quite powerful
When I execute a command using ProcessBuilder, how does it know where to look for that command? Using this hack/trick I've modified my PATH variable (verified by inspecting processBuilder.environment()) to be bad (empty, working dir, etc) but ProcessBuilder can still execute sort, echo, bash, etc. just fine. How is it doing this?!
Note: My particular development environment is OSX but this code will also run on Red Hat Enterprise Linux.
The documentation says
[...] a command, a list of strings which signifies the external program file to be invoked and its arguments, if any. Which string lists represent a valid operating system command is system-dependent. [...]
Which in essence mean that where it looks for programs to execute depends on the particular system and JVM you're running on.
I can't find a complete matrix of JVM / System behaviors, but supposedly it behaves similar to the popular shells of the system (bash for *nix and cmd for windows) i.e. it searches the directories in the PATH environment variable from left to right and executes the first executable file it finds.
If you want to take control of finding commands, then, well, take control of finding commands. Don't let ProcessBuilder search. Use your own code to find what you want to run, and then put an absolute pathname into the parameter to ProcessBuilder.
I am trying to run a perl command with Java runtime exec in linux/ubuntu/gnome. The command generates an pdf file, but it saves it in my home folder. Is there any way that the exec method can set an output path for the commands executed? Thanks in advance.
The exec method just runs the command on the operating system, so you'll want to change the command you're running with exec more than anything in "Java" per se.
There are a few possibilities:
Change the working directory of your java program. The .pdf is being saved in your working directory because this is where the program is being run.
Unfortunately it's not simple to change this value after the program has been launched. It is, however, trivial to change before the program starts; just change the working directory before starting the program.
Move the file to it's desired location after it's been created in your home directory.
Change the command so that it includes the target location. Your perl script may have an option that will enable you to save it's output to a certain location (usually -o or --output). Using this your program would change from:
Runtime.exec("perl someprogram");
to something like:
Runtime.exec("perl someprogram -o /path/to/some.file")
You might be able to use "output redirection", if there is no option to do this.
Try something like what's below as your argument:
Runtime.exec("perl someprogram > /path/to/some.file")
Unfortunately, without knowing more details of your situation I can't provide more concrete advice.
While each approach has benefits and drawbacks, it's probably best to just implement the one that you understand best; if you can't get one to work, try another.
A good, free online resource for learning is Introduction to Linux: A Hands On Guide.
Section 2.2 has details on cd which you can use for 1..
Section 3.3, section 3 teaches about the mv command, which will be useful in 2..
Section 5.1 is about I/O redirection. Knowing about "output redirection" and the > operator, are important for 4..
For 3., you'll have to consult the documentation of the perl program you're using.
You could modify the Perl script to accept an absolute path for the output.
You can trying setting the working directory using exec(java.lang.String[], java.lang.String[], java.io.File) where File is the directory the command is executed from.
If all else fails, you'll can always copy the generated file from the Home directory to your final location.