UNIX for Dummies Questions & Answers

Now I'm the one scratching my head, no idea what you're saying here. Maybe first off we should explain what a process is.

A process is an independent virtual memory space that a program can execute inside. It has its own independent set of memory, set of open files, and its own program context.

You get a sub-process when this process makes the fork() system call. It creates a near-perfect copy of the old process all the way down to open files and what instruction its currently running, with one significant difference: the 'child' process will have zero returned to it from the fork() call, while the 'parent' process will have the new process' PID returned to it. Based on that the same program can take different directions. Also, when the 'child' terminates, the 'parent' is told about it via a signal.

So, they're independent, but may share some things like files, and they know which created which.

The only process with no parent at all is process 1, init. All other processes are created by fork(). So a child process isn't some special kind of process apart, it's just a description of which process created which.

Whenever you run a shell script it's probably running in a sub-process. the shell forks off a new process and runs the script inside it.

Maybe although you would need to define what you mean with "executions", "primary executions" and clarify what "said instructions" are referring to.
Known means well, known, the opposite of unknown. In that context, it means the variable names and contents are reachable and usable by the subprocess.

...And the process-fork concept tells you why. The new process gets a copy of the memory of its parent, including environment variables, but after the fork these memory spaces are independent -- changes in either child or parent are not reflected in the other.

In this example script1 invokes script2. Parameters exported from script1 are available to script2.

Code:

#!/bin/ksh
# This is script1
#
# Getting environment variables ready for script2
export myparameter1="first_parameter_for_script2"
export myparameter2="second_parameter_for_script2"
# Invoke the subprocess called script2
# script2 will see all exported environment variables
echo "Starting: script1"
echo "myparameter1=${myparameter1}"
echo "myparameter2=${myparameter2}"
./script2
echo "Finishing: script1"


#!/bin/ksh
# This is script2
#
# Indenting the echoes by 5 spaces for visual effect
echo "     Starting: script2"
echo "     ${myparameter1}"
echo "     ${myparameter2}"
echo "     Finishing: script2"



./script1
Starting: script1
myparameter1=first_parameter_for_script2
myparameter2=second_parameter_for_script2
     Starting: script2
     first_parameter_for_script2
     second_parameter_for_script2
     Finishing: script2
Finishing: script1