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In this code I find a list all of the running java processes and give the below function a name to look for, it will do its best. But since I find my approach a little too ugly, could some POSIX shell script writer have a look and possibly give me some simplification recommendations?


#!/bin/sh

# here is an ugly constant vuze java process name
readonly vuze_java_process_name='org.gudy.azureus2.ui.swt.Main'

is_java_program_running()
# expected arguments:
# $1 = java program name
{
    # there will always be at least one java process:
    # jdk.jcmd/sun.tools.jps.Jps, which is actually
    # the program giving us the list of java processes
    java_process_list=$( jps -l | awk '{print $2}' )

    # this behaves strangely if there is zero processes (needs verification)
    # but since there is always at least one, no problem here
    java_process_list_count=$(( $( printf '%s\n' "${java_process_list}" | wc -l ) ))

    # set the result value as if we did not find it
    result=false

    # POSIX-ly simulate FOR loop
    i=1; while [ "${i}" -le "${java_process_list_count}" ]
    do
        # here we take one line from the list on $i position
        java_process_entry=$( echo "${java_process_list}" | sed --posix --quiet "${i}{p;q}" )
        # compare the given process entry with given java program name
        if [ "${java_process_entry}" = "${1}" ]
        then
            # set the result value
            result=true
            # end this loop
            break
        fi
        # increase iterator
        i=$(( i + 1 ))
    done

    # depending on if we found vuze process running,
    # return positive or negative result value
    if [ "${result}" = true ]
    then
        return 0
    else
        return 1
    fi
}

###
### EXAMPLE on Vuze
###

# keep Vuze alive forever, check in 5 seconds interval
while true
do
    sleep 5s

    if ! is_java_program_running "${vuze_java_process_name}"
    then
        my_date_time=$(date +%Y-%m-%d_%H:%M:%S)
        printf '%s  %s\n' "${my_date_time}" "(re-)starting Vuze"
        ( /home/vlastimil/Downloads/vuze/vuze > /dev/null 2>&1 & )
    fi
done
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2
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Instead of simulating a for (( expr1 ; expr2 ; expr3 )) loop, use a POSIX

    for java_process_entry in $java_process_list

Notice that now you don't need to compute the number of lines, neither invoke sed.


There is noting wrong with early return. return 0 as soon as the desired process is found.


There is no need to store the entire list in a variable, neither invoke awk. Process the jps output sequentially.

All that said, consider

    is_java_program_running()
    {
        jps -l | while read pid java_process_entry; do
            if [ $java_process_entry = "${1}" ]; then return 0; fi
        done
        return 1
    }
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1
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(On top of what @vnp already wrote.)


When these lines are the last in a function:

if [ "${result}" = true ]
then
    return 0
else
    return 1
fi

Then you can write simply:

[ "${result}" = true ]

Because the exit code of a function is the exit code of its last executed statement.

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  • \$\begingroup\$ In fact, given that the only other possible value of $result is false, we can just expand and execute it. \$\endgroup\$ – Toby Speight Feb 25 at 19:06

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