BackgroundProcess

#!/bin/bash
# Written by Manuel Iglesias. glesialo@gmail.com

CommandName=${0##*/}
CommandOptionString="-c"
RunInBackgroundOptionString="-b"
KillProcessOptionString="-k"
ProcessFinishedOptionString="-f"
TempDir="/tmp"
KillProcessTimeout="1" # Max time for killed process's parent to save child process' info. '$CommandName -k ' fails if parent still running after timeout.
KillSignal="TERM"
CommandLineVarName="CommandLine"    # Process info output.
ElapsedTime_mSVarName="ElapsedTime_mS"  # Process info output.
ExitCodeVarName="ExitCode"      # Process info output.
StandardOutVarName="StandardOut"    # Process info output.
StandardErrorVarName="StandardError"    # Process info output.



Usage() {
echo -e "'$CommandName' can be used to launch/control a process running in background.
Usage: '$CommandName $CommandOptionString Command [Param [Param...]]'.
\tLaunches 'Command [Param [Param...]]' in background.
\tOutputs background process Id. Exitcode 0 if successful.
Usage: '$CommandName ProcessPid'.
\tOutputs background process' info (See below).
\tExitcode 0 if process is valid and no longer running (Info valid).
\tExitcode 1 if process valid and still running (Info not valid).
\tExitcode non 0 if not a valid process or any other problems
\t (Info not valid).
Usage: '$CommandName $ProcessFinishedOptionString ProcessPid'.
\tChecks if process with 'ProcessPid' Pid has finished running.
\tExitcode 0 if process is valid and no longer running
\tExitcode 1 if process valid and still running.
\tExitcode non 0 if not a valid process or any other problems.
\tDoes not output any info.
Usage: '$CommandName $KillProcessOptionString ProcessPid'.
\tKills process with 'ProcessPid' Pid (Previously
\t launched by '$CommandName').
\tOutputs background process' info (See below).
\tExitcode 0 if valid process and killed successfully
\t (Or had exited already) and info read successfully.
Background process' info:
\tText that, when parsed, provides the following variables and values:
\t '$CommandLineVarName': Command and parameters of process when launched.
\t '$ElapsedTime_mSVarName': Process' running Time (MilliSeconds).
\t '$ExitCodeVarName': Exit code of process.
\t '$StandardOutVarName': Output generated by process while running.
\t '$StandardErrorVarName': Error output generated by process while running.
\tNote: Parsing notes in: System_Docs/System/BashCodeRepository.
Note: Normal usage sequence:
\tLaunch a process in background and get its Pid.
\tDo other tasks.
\tCheck if backgroung process has finished running
\t using '$CommandName' and Pid.
\tRead info when backgroung process has finished.
\tParse background process' info and use Variables' contents.
\tIf background process has not finished in the allotted time
\t kill it with '$CommandName' (And get info of killed process).
Please read System_Docs/System/BashCodeRepository for examples of usage.
" 1>&2
return 0
}



CommandOption=false;RunInBackgroundOption=false;KillProcessOption=false;ProcessFinishedOption=false
if [[ "$1" == "$CommandOptionString" ]]
  then
    CommandOption=true
    shift
  else
    if [[ "$1" == "$RunInBackgroundOptionString" ]]
      then
        RunInBackgroundOption=true
        shift
      else
        if [[ "$1" == "$KillProcessOptionString" ]]
          then
            KillProcessOption=true
            shift
          else
            if [[ "$1" == "$ProcessFinishedOptionString" ]]
              then
                ProcessFinishedOption=true
                shift
            fi
        fi
    fi
fi

if [[ $# -lt 1 || "$1" == "-h" || "$1" == "-?" || "$1" == "--help" || "$1" == "-help" ]]
  then
    Usage
    exit 64
fi

if $CommandOption
  then
    if ! type "$1" &>/dev/null
      then
        echo -e "$CommandName: Command '$1' not in '\$PATH'. Aborting!" 1>&2
        exit 127
    fi
#   'coproc': Equivalent to ending command with '&'. '&' does not work if shell invoked with `` (ProcessId=`BackgroundProcess -c Command`).
#   &>/dev/null so that no error message is given when killed. Also to allow background processes to be launched from this background process (pipes?).
    if coproc $CommandName $RunInBackgroundOptionString "$@" &>/dev/null
      then
        eval "exec ${COPROC[0]}>&-" # Close coproc stdout pipe (See Books/Science/Computer_Science/Linux/Bash_scripting/Bash_Co_Processes).
        eval "exec ${COPROC[1]}<&-" # Close coproc stdin pipe (See Books/Science/Computer_Science/Linux/Bash_scripting/Bash_Co_Processes).
        echo "$!"
        exit 0
      else
        echo -e "$CommandName: Launching in background with 'coproc' failed with ExitCode: $?. Aborting!" 1>&2 # Should never happen but... just in case ;-).
        exit 70
    fi
fi

if $RunInBackgroundOption
  then
    TempFile="${TempDir}/${CommandName}_$$"
    TempErrorFile="${TempFile}.Error"
    >$TempErrorFile         # So that other users can not read file.
    chmod 600 $TempErrorFile        # So that other users can not read file.
    TempOutFile="${TempFile}.Out"
    >$TempOutFile           # So that other users can not read file.
    chmod 600 $TempOutFile      # So that other users can not read file.
    cd $TempDir # So that child process uses it as working directory (And does not tie up current wd).
    exec 0<&- # Close stdin.
    exec 1>&- # Close stdout.
    exec 2>&- # Close stderr.
    StartTime=$(date +%s.%N) # Seconds.Nanoseconds since 1970−01−01.
    Decimals=${StartTime##*\.}          # Fast Times1000.
    Decimals=${Decimals:0:3}            # Fast Times1000.
    StartTime="${StartTime%\.*}$Decimals"   # Fast Times1000.
    1>$TempOutFile 2>$TempErrorFile "$@"
    ExitCode=$?
    EndTime=$(date +%s.%N) # Seconds.Nanoseconds since 1970−01−01.
    Decimals=${EndTime##*\.}            # Fast Times1000.
    Decimals=${Decimals:0:3}            # Fast Times1000.
    EndTime="${EndTime%\.*}$Decimals"       # Fast Times1000.
    ((ElapsedTime_mS = EndTime - StartTime))
    echo -e "${CommandLineVarName}=\"$@\"
#
${ElapsedTime_mSVarName}=${ElapsedTime_mS}
#
${ExitCodeVarName}=${ExitCode}
#
${StandardOutVarName}=\"$(cat $TempOutFile)\"
#
${StandardErrorVarName}=\"$(cat $TempErrorFile)\"
#" >$TempFile
    chmod 600 $TempFile # So that other users can not read file.
    rm -f $TempErrorFile $TempOutFile
    exit 0
fi

if [[ $# -ne 1 ]]
  then
    Usage
    exit 64
fi

TempFile="${TempDir}/${CommandName}_$1"

if ProcessCommandName=$(2>/dev/null ps --pid=$1 h -o comm)
  then
    if [[ "$CommandName" == "${ProcessCommandName}${CommandName#${ProcessCommandName}}" ]] # 'ps' returns only the 15 first characters of command.
      then
        if $KillProcessOption
          then
            for Child in $(ps -o pid --no-headers --ppid $1)
              do
                pkill -${KillSignal} -P $Child &>/dev/null # Kill BackgroundProcess' Child's children (grandchildren).
              done
            pkill -${KillSignal} -P $1 &>/dev/null # -P means kill processes whose parent process ID is listed. Here: kill BackgroundProcess' children.
            ((KillProcessTimeout *= 10)) # Will be checked every 1/10 seconds.
            while &>/dev/null ps --pid=$1 && [[ $KillProcessTimeout -gt 0 ]]
              do
                sleep 0.1
                ((KillProcessTimeout--))
              done
            if &>/dev/null ps --pid=$1
              then
                echo -e "$CommandName: Warning! Process '$1' could not be killed." 1>&2
                exit 70
              else
                if [[ -f $TempFile ]]
                  then
                    cat $TempFile
                    rm -f $TempFile
                    exit 0
                  else
                    echo -e "$CommandName: Process killed but temporary file not found. No record of process '$1'." 1>&2
                    exit 70
                fi
            fi
        fi
        echo -e "$CommandName: Process '$1' still running." 1>&2
        exit 1
      else
        echo -e "$CommandName: Process '$1' running but not an instance of '$CommandName'. Aborting." 1>&2
        exit 70
    fi
fi

if [[ -f $TempFile ]]
  then
    if $ProcessFinishedOption
      then
        exit 0
    fi
    if $KillProcessOption
      then
        echo -e "$CommandName: Process '$1' has already exited. Kill request ignored." 1>&2
    fi
    cat $TempFile
    rm -f $TempFile
  else
    echo -e "$CommandName: Process not running and temporary file not found. No record of process '$1'." 1>&2
    exit 70
fi