Develop Reference

Shell command in Java with Runtime.getRuntime().exec();

Is this a simple and good way to execute a Shell command via Java?
Runtime.getRuntime().exec( some command );
Or is this bad practice?

It depends.
The original purpose and basic functionality of a Unix shell is to let you run programs, optionally passing them arguments. For example the command ls runs the ls program, and the command grep foo bar runs the grep program with the arguments foo and bar. If your command only runs a (fixed) program with fixed if any arguments, Runtime.exec can do it. There are two subcases:
the overloads taking a String parse the line into 'words' (program name and arguments) using any whitespace; this is essentially the same as the default parsing (with no quoting) done by standard shells.
if you need any different parsing, for example if your command would use any quoting in shell, you must do that parsing yourself and pass the results to one of the overloads taking a String[].
But note that when you run a program from an interactive shell -- one using a terminal or equivalent (sometimes called a console) for input and output -- the program's input and output default to that terminal. The I/O for a program run by Runtime.exec is always pipes from and to the Java process, and some programs behave differently when their input and/or output is/are pipe(s) -- or file(s) -- instead of a terminal. Plus you must write code to send (write) any desired input and receive (read) any output. Of course, shells can be and sometimes are run without a terminal too.
However, shells can be and routinely are used to do much much more than the basics:
shell can execute commands with contents different from the input by variable (formally parameter) substitution (possibly with modification/editing), command substitution, process substitution, special notations like squiggle and bang, and filename expansion aka 'globbing' (so called because in the early versions of Unix it was done by a separate program named glob). Runtime.exec doesn't do these, although you can write Java code to produce the same resulting command execution by very different means.
shell executes some commands directly in the shell rather than by running a program, because these commands affect the shell process itself,
like cd umask ulimit exec source/. eval exit alias/unalias, or variables in the shell like set shift unset export local readonly declare typeset let read readarray/mapfile,
or child process like jobs fg bg, or special parsing like [[ ]] and (( )) (in some shells). These are called 'builtin' and Runtime.exec can't do them,
with two partial exceptions: it can run a program with a different working directory and/or env var settings, equivalent to having previously executed cd or export or equivalent.
Shell also often has builtins that duplicate, or modify, a 'normal' program; these commonly include test/[ echo printf kill time. Runtime.exec can only do the program version, not the builtin version.
shell has control structures (compound commands) like if/then/else/elif/fi and while/for/do/done and trap && || ( ) { }. Runtime.exec can't do these, although in some cases you could use Java logic to produce the same results.
shell can also have user-defined functions and aliases that can be used as commands; Runtime.exec does not.
shell can redirect the I/O of programs it runs, including forming pipes. Runtime.exec can't do these, but see below.
Since 1.5, Java also has ProcessBuilder, which provides the same functionality and more, in a more flexible and arguably clearer API, and thus is generally recommended instead. ProcessBuilder does support redirecting I/O for the program it runs, including using the terminal/console if the JVM was run on/from one (which is not always the case), and since 9 it can build a pipeline. It does not have the word-splitting functionality of Runtime.exec(String) but you can easily get the same result with string.split("[ \t]+") or in most cases just " +".
Note shell is itself a program, so you can use either Runtime.exec or ProcessBuilder to run a shell and pass it a command, either as an argument using option -c (on standard shells at least) or as input, and unsurprisingly this shell command can do anything a shell command can do.
But this can be a portability issue because different systems may have different shells, although any system claiming Unix certification or POSIX conformance must have a shell named sh that meets certain minimum requirements.
The actual shell used on different systems might be any of bash dash ksh ash or even more. OTOH this is true for other programs as well; some programs that typically differ significantly on different systems are awk sed grep and anything to do with administration like netstat.
A few of the existing Qs that show shell commands that don't work in Runtime.exec at least as-is:
a command for sherlock.py is interpreted differently from linux command line and java process api
Execute shell script multiple commands in one line using Process Builder in Java (Unix)
Check in Java if a certain application is in focus
Problem in executing command on AIX through Java
ProcessBuilder doesn't recognise embedded command
File not Found when executing a python scipt from java
Java system command to load sqlite3 db from file fails
Curl To Download Image In JAVA
Keytool command does not work when invoked with Java
use javap from within a java program on all the files
Using SSMTP and ProcessBuilder
Process Builder Arguments
Whitespace in bash path with java
java.lang.Runtime exception "Cannot run program"
Why does Runtime.exec(String) work for some but not all commands?
How to save Top command output in a text or csv file in java?
Execute bash-command in Java won't give a return
Using Java's Runtime.getRuntime().exec I get error with some commands, success with others -- how can this be determined?
Java and exec command - pipe multiple commands
Java exec() does not return expected result of pipes' connected commands
How to make pipes work with Runtime.exec()?
How to use Pipe Symbol through exec in Java
In Runtime.getRuntime().exec() getting error: /bin/bash: No such file or directory
Java exec linux command
How to use pipes in a java Runtime.exec
Java Runtime.getRuntime().exec and the vertical bar
Whenever I execute terminal command from code it gives "cannot run program" error=2 No such file or directory
Command line proccess read linux in java
Java Command line system call does not work properly

How can I execute .jar file from the terminal without specifying its name

How can I execute .jar file in folder from the Windows cmd without specifying its name.
I have tried below command (as there is only 1 jar in that folder I used *) but its not working(Error: Unable to access jarfile *.jar
).
java -jar *.jar

I am not sure it would be a good idea to just run everything in a directory, but you could:
FOR %A IN ("*.jar") DO (java -jar "%~A")

So what you appear to be asking is how to run the command
% java -jar somelongname.jar
as
% java -jar *.jar
to avoid some typing. That's not possible, because neither the Windows CMD shell or the java command is going to expand the *.jar wildcard pattern.
(On Linux / Unix / MacOS, the shell does wildcard expansion before passing arguments to a command. On Windows, it is the responsibility of the command to do this. In practice, it appears that the java command only expands wildcards in the arguments that are going to be passed to your application; see Stop expanding wildcard symbols in command line arguments to Java)
So if you want to avoid typing those pesky characters on Windows, you will need to do something like:
write a simple BAT file to run "java -jar somelongname.jar", or
write a clever BAT file to identify and run a JAR file that matches "*.jar", or
use Powershell.
For what it is worth, I think what you are trying to do is rather dangerous. This is a bit like typing "di*" to run the "dir". What if there is some other more dangerous command on the PATH that is going to match instead of "dir"?

Restarting process on -XX:OnOutOfMemoryError using shell script gives: Unrecognized option: -9

I'm trying to restart process when OOME happens. Java binary is launched using two shell scripts, one of them imports other. I don't have any control of the first one but can modify the second one as I want.
This is a prototype what I'm trying to do:
First shell script test.sh:
#!/bin/sh
JAVA_OPTS="$JAVA_OPTS -Xmx10m"
. test1.sh
echo $JAVA_OPTS
java $JAVA_OPTS $es_params TestMemory
Second shell script test1.sh:
#!/bin/sh
pidfile="test.pid"
touch $pidfile
params="$parms -Dpidfile=$pidfile"
kill_command="kill -9 \$(cat $pidfile)"
dir=$( cd $(dirname $0) ; pwd -P )
path="$dir/$(basename $0)"
start_command="$path $#"
restart_command="$kill_command;sleep 2;$start_command"
JAVA_OPTS="$JAVA_OPTS -XX:OnOutOfMemoryError=\"$restart_command\""
Generally what it does is JAVA_OPTS is constructed inside test1.sh and then used to run Java binary, which just writes PID in pidfile and then creates OOME.
Problem happens during execution, java can't understand what is a parameter and what is a class to run. I think it might be a problem of quoting, I tried different ways to escape JAVA_OPTS, but without any result. I'm either getting:
Unrecognized option: -9
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
Or
Error: Could not find or load main class "-XX:OnOutOfMemoryError=kill
If I just take a value of JAVA_OPTS and put it manually in test.sh it runs perfectly.
Any ideas how can I change test1.sh to make it work? I think I tried almost every possible way of putting double and single quotes, but without any success. Also if I put restart_command in restart.sh file and use it instead of the variable, it works fine.
After running set -x I saw that shell modifies every single space character to ' ' - adds ' on both sides. Escaping doesn't gives any result. Any idea how to avoid this? So final commend is:
+ java -Xmx10m '"-XX:OnOutOfMemoryError=kill' '$(cat' 'test.pid);sleep' '2;/Users/davidt/test/TestMemory/bin/test.sh' '")' -Des.pidfile=test.pid TestMemory
Update
I can run simplified command successfully
java "-XX:OnOutOfMemoryError=echo 'Ups'" $es_params TestMemory
But it seems a general problem, shell just hates spaces into variables I guess:
JAVA_OPTS="\"-XX:OnOutOfMemoryError=echo 'Ups'\""
set -x
java $JAVA_OPTS TestMemory
This script fails and the last line is interpreted as:
java '"-XX:OnOutOfMemoryError=echo' ''\''Ups'\''"' TestMemory
I tried different options to escape

This is a shell problem. Based on the evidence, I'd say that one of the ; characters ... and possibly some why space ... is being interpretted by the shell when you don't want / need this to happen.
If you run set -x in the shell before running the command that is trying to start the JVM, you will see the actual command that is being used.
It seems shell translates every single space to ' ',
Not exactly. The single quotes are inserted by the shell into the output you are getting from set -x. They simply indicating where the argument boundaries are. They are not really there ... and they are certainly NOT being passed to the java command.
Any idea how to [a]void it?
What you need to do is start from the (final) command that you are trying execute ...
java -Xmx10m -XX:OnOutOfMemoryError="kill NNNN;sleep 2;/Users/davidt/test/TestMemory/bin/test.sh" -Des.pidfile=test.pid TestMemory
... and work backwards, so that the shell variables, expansions and escaping give you what you need.
The other thing to note is that this:
java -Xmx10m -XX:OnOutOfMemoryError="kill $(cat test.pid); ..."
probably won't work. The kill $(cat test.pid) command is using shell syntax and requires shell functionality to interpolate the contents of the PID file. I doubt that the JVM is going to know what to do with that. (Or more accurately. It will do what you have literally told it to do, but that will not be what you want ...)
If you really need to interpolate the pid file content when the restart command is run as you appear to be trying to do, then suggest that turn the restart command into a free-standing shell script, and set the file mode so that it is executable. It will be simpler and a lot easier to get working.
As a general piece of advice, is is a bad idea to be too clever with shell scripts. The exact semantics of variable expansion and command parsing are rather tricky, and it is easy to get yourself really confused ... if you are trying to do this at multiple levels.

I ended up put the script I wanted to execute in a separate file and gave it as a parameter to JVM to execute when OOME happens.
echo "echo 'UPS'" >> oome_happened.sh
JAVA_OPTS="\"-XX:OnOutOfMemoryError='oome_happened.sh'\""
set -x
java $JAVA_OPTS TestMemory

Like #DaTval said, you should put the command in a script. The script should be someting like.
#!/bin/bash
kill -9 $PPID
Kill the caller of scripts.

run java.exe with arguments from powershell

I'm trying to call wlst/jython/python from powershell
set classpath with setWLSEnv.cmd is not set in the right session? so I have tried to set -cp as argument
& C:\bea\tpc\weblogic1033\server\bin\setWLSEnv.cmd;
$cp='C:\bea\tpc\WEBLOG~1\server\lib\weblogic.jar'
$wlst='weblogic.WLST'
$script='C:\domains\tpc\Domain\bin\status.py'
$java="C:\PROGRA~1\Java\JROCKI~1.0\bin\java"
& "$java $cp $wlst $script"
#or
. "`"$java`" -cp `"$cp`" $wlst `"$script`""
#or
& "`"$java`" -cp `"$cp`" $wlst `"$script`""
I have tried to quote the command string in various ways without success
The term '"C:\PROGRA~1\Java\JROCKI~1.0\bin\java" -cp "C:\bea\tpc\WEBLOG~1\server\lib\weblogic.jar" weblogic.WLST "C:\domains\tpc\SasTT
pcDomain\bin\status.py"' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of
the name, or if a path was included, verify that the path is correct and try again.
At C:_WORK_\SAS\statusAll.ps1:15 char:2
+ . <<<< ""$java" -cp "$cp" $wlst "$script""
+ CategoryInfo : ObjectNotFound: ("C:\PROGRA~1\Ja...\bin\status.py":String) [], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException

When you use the call operator &, the next token needs to be the name of a command and nothing else. So instead of this:
& "$java $cp $wlst $script"
Try this:
& $java $cp $wlst $script
Sometimes getting arguments to native exes can get ugly. A technique that usually works but is unsafe if any of your arguments come from user input is this:
Invoke-Expression "$java $cp $wlst $script"

In addition to the trouble with how you're formatting your command into a string, setWLSEnv.cmd is a script for the Windows Command Prompt. PowerShell cannot execute this file; it does not know how to interpret it, much like how Notepad does not know how to interpret a docx file. Windows associates .cmd files with the command prompt, so your first line is equivalent to
& cmd.exe /c C:\bea\tpc\weblogic1033\server\bin\setWLSEnv.cmd
(Note that the semicolon is unnecessary since you don't have any other commands on the same line.)
This creates a new process using cmd.exe. This new process executes the batch file, setting the environment variables you expect, and then the process exits, discarding the environment changes.
If you need setWLSEnv.cmd to set environment variables prior to executing your program, you should write a batch file that calls it instead of a PowerShell script. Otherwise, you will need to find or write a PowerShell equivalent to set up your environment.

Java option -XX:OnOutOfMemoryError does not work when called through exec in bash script

I have a java application and I want to run a script whenever it experiences and OutOfMemoryException
This works great:
$ java -server -XX:OnOutOfMemoryError="./oom_script %p" TestOOMClass
Unfortunately my application is run by a bash script in production. The script boils down to this:
cmd='java -server -XX:OnOutOfMemoryError="./oom_script %p" TestOOMClass'
##does a lot of checking and cmd building here
exec -a app ${cmd}
When run like this java never respects the double quotes and thinks %p is the class. how do I prevent this? I've tried double escaping but that doesn't work.

Since your program is run as a shell script, I would suggest putting this as the first line in your shell script after the shebang:
set -xv
Then, in the crontab, put 2>&1 at the end of the command line, so STDERR and STDOUT are merged. Crontab usually emails out the STDOUT of a command to root, so you can see what the output is. If not, then apend the following to the end of the command in your crontab:
> /somedir/output.$$ 2>&1
Make sure somedir exists, and after crontab runs your command, you'll see the verbose and debug output. Each line in your shell script will be displayed before it is executed -- both as written and as the shell actually interprets it.
The set -xv becomes very useful in debugging any sell script. There could be all sorts of environmental issues involved between the cronjob and the script running under your login. You might even find a shell issue. For example, crontab usually executes shell scripts in Bourne shell and you probably have Bash or Kornshell as your default shell. Whatever it is, you'll usually find out the issue very quickly when you turn on verbose/debug mode.
You don't even have to do this to the entire script. You can put set -xv anywhere in your script to turn on verbose/debug mode, and set +xv to turn it off.
I could make several pious high minded recommendations (use quotes, don't assume environment things, prefix your command line with "bash -c" to make sure you're using the right shell, etc.), but this would be guessing what could be wrong. In order to really debug this issue, I would need to see the machine, know the OS, see your entire shell script, and understand the entire environment. And, the first thing I would do is add set -xv in your shell script.

Quotes and escaping is an art. I would suggest you add echo ${cmd} before calling exec so you can see what it looks like then.
I would suggest using
cmd='java -server -XX:OnOutOfMemoryError=\\"./oom_script %p\\" TestOOMClass'
instead (untested). You need it to look like \" when being echoed.

an alternative i suggest (to bypass the problem, not solve it indeed) is to rung and bash script and access the $PPID:
PPID The process ID of the shell's parent. This variable is readonly.
then kill the process with that ID (please bare in mind that is an untested suggestion)