The aim of this page📝 is to explain extracting process information and start timestamps in bash based on the particular example of using jobs and ps commands.

Pavol Kutaj

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Mar 29, 2024

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• The jobs command lists the current jobs in the shell, including job IDs and statuses, but does not include the start timestamp.
• The ps command displays information about processes, such as process IDs (PIDs) and start times. However, it cannot directly take job IDs as input to print the start timestamp.
• Using ps -p {{PID}} -o lstart retrieves the start timestamp of a process with a specific PID.
• Extracting the PID from the jobs command output can be done using awk or cut.
• awk '{print $2}' extracts the second field from each line of input.
• cut -d' ' -f2 extracts the second field based on a delimiter — you could do that as an alternative. I am finding awk more elegant here.
• The function get_job_start_time() parses jobs -l, extracts the PID, and retrieves the start timestamp.

CODE

get_last_job_start() {
    # prints the start time of the last background job (no matter what status)
    local last_job
    local pid
    last_job=$(jobs -l | tail -n 1)
    if [ -n "$last_job" ]; then
        pid=$(echo "$last_job" | awk '{print $2}')
        if [ -n "$pid" ]; then
            ps -p "$pid" -o lstart
        else
            echo "Failed to extract job ID"
        fi
    else
        echo "No background jobs found"
    fi
}