Pass return value of a function in background process

02-15-2016

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If you need really put something to do in background, then do something (parallel) and after that wait the child process to end, solution could be something like:

Code:

child()
{
  parentfile=$1

  do_something
  stat=$?

  echo "mypid=$$
           mystat=$stat" > $parentfile
}


#########
# MAIN

# file to use get answer from child process
childfile=$$.child.txt

# start child
child $childfile >/dev/null 2>&1  &
# save child process PID
CHILDPID=$!

do_something

# wait child process to end
wait $CHILDPID

# source childfile answer
. $childfile
# and destroy it
rm -f $childfile 2>/dev/null 

# use values
echo "child pid=$mypid"
echo "stat=$mystat"

Other method is to use event methods to communicate between process (trap + kill). Use file to move values between process. I like more event methods. There are not any shared variables. Of course you can use also named pipes between process. Source file is so easy.

kshji

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jrunscript(1) General Commands Manual jrunscript(1) NAME
jrunscript - command line script shell SYNOPSIS
jrunscript [ options ] [ arguments... ] PARAMETERS
options Options, if used, should follow immediately after the command name. arguments Arguments, if used, should follow immediately after options or command name. DESCRIPTION
jrunscript is a command line script shell. jrunscript supports both an interactive (read-eval-print) mode and a batch (-f option) mode of script execution. This is a scripting language independent shell. By default, JavaScript is the language used, but the -l option can be used to specify a different language. Through Java to scripting language communication, jrunscript supports "exploratory programming" style. NOTE: This tool is experimental and may not be available in future versions of the JDK. OPTIONS
-classpath path Specify where to find the user's .class files that are accessed by the script. -cp path This is a synonym for -classpath path -Dname=value Set a Java system property. -Jflag Pass flag directly to the Java virtual machine on which jrunscript is run. -l language Use the specified scripting language. By default, JavaScript is used. Note that to use other scripting languages, you also need to spec- ify the corresponding script engine's jar file using -cp or -classpath option. -e script Evaluate the given script. This option can be used to run "one liner" scripts specified completely on the command line. -encoding encoding Specify the character encoding used while reading script files. -f script-file Evaluate the given script file (batch mode). -f - Read and evaluate a script from standard input (interactive mode). -help Output help message and exit. -? Output help message and exit. -q List all script engines available and exit. ARGUMENTS
If [arguments...] are present and if no -e or -f option is used, then the first argument is the script file and the rest of the arguments, if any, are passed as script arguments. If [arguments..] and -e or -f option are used, then all [arguments..] are passed as script argu- ments. If [arguments..], -e and -f are missing, interactive mode is used. Script arguments are available to a script in an engine variable named "arguments" of type String array. EXAMPLES
Executing inline scripts jrunscript -e "print('hello world')" jrunscript -e "cat('http://java.sun.com')" Use specified language and evaluate given script file jrunscript -l js -f test.js Interactive mode jrunscript js>print('hello world'); hello world js>34 + 55 89 js> thread(function() { print('hello world'); } hello world js> Run script file with script arguments jrunscript test.js arg1 arg2 arg3 test.js is script file to execute and arg1, arg2 and arg3 are passed to script as script arguments. Script can access these using "argu- ments" array. SEE ALSO
If JavaScript is used, then before evaluating any user defined script, jrunscript initializes certain built-in functions and objects. These JavaScript built-ins are documented in jsdocs. 06 Aug 2006 jrunscript(1)

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