How to get result from background process linux shell script? -

for example let's want count number of lines of 10 big files , print total.

for f in files     #this creates background process each file     wc -l $f | awk '{print $1}' & done 

i trying like:

for f in files     #this not work :/     n=$( expr $(wc -l $f | awk '{print $1}') + $n ) & done  echo $n 

you should use gnu parallel:

find . -maxdepth 1 -type f | parallel --gnu 'wc -l' | awk 'begin {n=0} {n += $1} end {print n}' 

or else xargs in parallel mode:

find . -maxdepth 1 -type f | xargs -n1 -p4 wc -l | awk 'begin {n=0} {n += $1} end {print n}' 

another option, if doesn't fit needs, write temp files. if don't want write disk, write /dev/shm. ramdisk on linux systems.

#!/bin/bash  declare -a temp_files  count=0 f in *   if [[ -f "$f" ]];     temp_files[$count]="$(mktemp /dev/shm/${f}-xxxxxx)"     ((count++))   fi done  count=0 f in *   if [[ -f "$f" ]];     cat "$f" | wc -l > "${temp_files[$count]}" &     ((count++))   fi done  wait  cat "${temp_files[@]}" | awk 'begin {n=0} {n += $1} end {print n}'  tf in "${temp_files[@]}"   rm "$tf" done 

by way, can though of map-reduce wc doing mapping , awk doing reduction.