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I have commands in a bash script that are similar to this:

eval "( java -classpath ./ $classname ${arguments[@]} $redirection_options $file )" &
pid=$!

However if I do a ps $pid it shows the main script process instead of the process of the java program.

It obtains the correct process when I omit the eval, but in order to get some of the complicated arguments to work correctly I need to use it.

Any idea of how I can get the PID of the java program when it's executed within an eval command?

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  • TL;DR: use $! after your line with the ampersand & (such as myprogram &)
    – i_want_more_edits
    Commented Jul 19, 2022 at 15:01

1 Answer 1

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Your ampersand is backgrounding the eval line, causing the (top-level) shell to fork a child, the child shell to eval the string and in turn run your java program as a grandchild of the top-level shell. So, $! reports the pid of the child shell, which is the most recently backgrounded command.

Instead move the backgrounding inside your eval:

eval "(java ...) &"
pid=$!

As long as the parenthetical doesn't get complicated enough to become a subshell, the above will work.

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  • 1
    Yes, this is it :) EXPR="java -jar test.jar &"; eval $EXPR; echo $! should do
    – barti_ddu
    Commented Dec 2, 2010 at 21:19
  • FYI: I noticed this works from a terminal but if you have a script with an icon on the desktop, it doesn't work.
    – Mike Q
    Commented Oct 18, 2013 at 18:36
  • Make sure to add " double quotes around the expression being evaluated, and also make sure to add the & inside those double quotes, just before the final double quote.
    – Roel Van de Paar
    Commented Aug 22, 2020 at 1:49

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