cat_and_bash_subprocesses.sh

#!/usr/bin/env bash                                                                                                                                                                          
                                                                                                                                                                       
# 'cat' seems to take multiple file descriptors (fd) - vaguely analgous to pointers - 
# and queues them, polling for available data and outputting it in a blocking FIFO manner. 
# It moves onto the next fd condition on the closing of the last.

function cat_subprocess_handeling() {                                                                                                                                            
    START=${SECONDS}                                                                                                                                                                                                                                                                                                                                    
    cat -- \                                                                                                                                                                                 
        <(                                                                                                                                                                                   
        # First FD redirct                                                                                                                                                                   
        START=${SECONDS}                                                                                                                                                                     
        echo "[1] pid:${$}"                                                                                                                                                                  
        { (sleep 3; echo "[1.1] pid:${$}"; echo "[1.1] Attempting to background..."; echo "[1.1] test 1"; echo "[1.1] test 2") & };                                                          
        END=${SECONDS}                                                                                                                                                                       
        ELAPSED=$(( END - START ))                                                                                                                                                           
        echo "[1] Executed in ${ELAPSED}"                                                                                                                                                    
    ) <(                                                                                                                                                                                     
        START=${SECONDS}                                                                                                                                                                     
        echo "[2] pid:${$}"; echo "[2] sleep test 1"; sleep 1; echo "[2] sleep test 2"                                                                                                       
        END=${SECONDS}                                                                                                                                                                       
        ELAPSED=$(( END - START ))                                                                                                                                                           
        echo "[2] Executed in ${ELAPSED}"                                                                                                                                                    
    ) <(                                                                                                                                                                                     
        START=${SECONDS}                                                                                                                                                                     
        echo "[3] pid:${$}";{ sleep 3 && echo "[3] async test 1" & };echo "[3] async test 2"                                                                                                 
        END=${SECONDS}                                                                                                                                                                       
        ELAPSED=$(( END - START ))                                                                                                                                                           
        echo "[3] Executed in ${ELAPSED}"                                                                                                                                                    
    )                                                                                                                                                                                                                                                                                                                                                     
    END=${SECONDS}                                                                                                                                                                           
    ELAPSED=$(( END - START ))                                                                                                                                                               
    echo "cat took ${ELAPSED} seconds to complete"                                                                                                                                           
}                                                                                                                                                                                            
                                                                                                                                                                                             
# time how_do_cat_and_subprocesses_interact                                                                                                                                                  
# START TIME - 15781                                                                                                                                                                         
# [1] pid:18994                                                                                                                                                                              
# [1] Executed in 0                                                                                                                                                                          
# [1.1] pid:18994                                                                                                                                                                            
# [1.1] Attempting to background...                                                                                                                                                          
# [1.1] test 1                                                                                                                                                                               
# [1.1] test 2                                                                                                                                                                               
# [2] pid:18994                                                                                                                                                                              
# [2] sleep test 1                                                                                                                                                                           
# [2] sleep test 2                                                                                                                                                                           
# [2] Executed in 1                                                                                                                                                                          
# [3] pid:18994                                                                                                                                                                              
# [3] async test 2                                                                                                                                                                           
# [3] Executed in 0                                                                                                                                                                          
# [3] async test 1                                                                                                                                                                           
# END TIME - 15784                                                                                                                                                                           
# cat took 3 seconds to complete                                                                                         
#                                                                                                                                                                                            
# real  0m3.003s                                                                                                                                                                             
# user  0m0.000s                                                                                                                                                                          
# sys   0m0.000s