wait_and_func_example.sh

#!/bin/bash

#This simple code demonstrates how to define a function, local and global variables in bash.
#And most importantly, how to launch background processes and wait for their termination
gvar="Glob value"
ncalls=0
avar="Test"
# Note for ksh users: in ksh to mark a function definition you should use either  function keyword
# or () after the function name, not both 
function a_proc(){
    echo ${gvar}
    local avar=$1 #ksh users: use 'typeset' instead of 'local'
    echo "Input: ${avar}"
    sleep 100
    avar=$(date)
    echo "Output: ${avar}"
    ncalls=$((${ncalls} + 1)) 
}

a_proc "$(date)" &
a_proc "$(date)" &
a_proc "$(date)" &
a_proc "$(date)" &
a_proc "$(date)" &
a_proc "$(date)" &
wait
#Although I am trying to update ${ncalls} assuming that this will change my global variable, but ...
#This is because I am launching the function in background, which works in a subshell, 
#so global variables won't be updated
echo "ncalls=${ncalls}"

echo "avar=${avar}"

##But look what happens with ncalls when launched in foreground
a_proc "$(date)"
echo "ncalls=${ncalls}"

##Conclusion: the local keyword (for bash, use typeset for ksh) can be useful if you want to make sure that you are not 
##changing a global variable in your function