bash_process_capture.sh

# BASH Gist:
# Get the PID, standard out, standard error, and the exit code of a process
# Here we simulate a single program by running a subprocess with () in the background,
# just long enough to get the PID and start waiting on it to finish.
# The PID is nice to have available to query the status of the program or to send it a SIGNAL
#

# Step 1: Run the process in the background
# This set of commands simulates a single process that writes to stderr, stdout, and returns
# exit code 42
#
# '>'  redirects stadard out
# '2>' redirects standard err
# '&'  puts the process in the background at the next step
# '#'
( echo Sleeping... ; sleep 10 ; echo "Good morning" >&2 ; exit 42)  > stdout.txt 2> stderr.txt  &

# Step 2: Collect PID, wait, and collect results
# This set of commands:
# * Uses the spcial variable $! to access the PID of the previous process placed in the background
# * Calls the 'wait' command with the PID as the argument, which in turn waits for the process with that PID to complete
# * Uses the special variable $? to access the exit code of the process
# * Uses 'wait' to get the PID and to wait for the process to complete
echo -e "\nPID : $!" ; wait $! ; echo "EXIT: $?" ; echo "Standatd Out:" ; cat stdout.txt ; echo "Standard Error:" ; cat stderr.txt ;

PID : 60974
[1]+  Exit 42                 ( echo Sleeping...; sleep 10; echo "Good morning" 1>&2; exit 42 ) > stdout.txt 2> stderr.txt
EXIT: 42
Standatd Out:
Sleeping...
Standard Error:
Good morning



# Here's a more realistic looking example that captures a few other details of the process...
# Let's say we have a text file created with:
echo -e "one\ntwo\nThree\nfour\nFIVE\nsix\nSeven\neight\nine\nTeN"
#
# So, contents are...
Zero
One
Two
Three
Four
Five
Six
Seven
Eight
Nine
teN

# ...And we want to know how many files are in the system's
# home directories with the digital representation of the numbers as their file names...

# The same standard out and error redirection, plus
# * Save the exit code to a file
# * Save the command line to a file

# Let's pipe a few commands in order to:
# 1. Find all lines in the file containing the names of digits.
# 2. Sort that list so we can ...
# 3. ...Reduce that list to a list of unique digits found.
# 3. Then send those digits as arguments to 'xargs' ...
# 4. Which, in turn, executes a 'find' command to locate all files under the /home/ directory whose names match those digits
# In the process, it also:
# * Saves the search results to search-results.log
# * Saves any error messages to search-errors.log
# * Saves the exit codes of all progams in the pipe stream 
# 
sed 's/^Z.*/0/;s/^O.*/1/gI;s/^Tw.*/2/gI;s/^Th.*/3/gI;s/^Fo.*/4/gI;s/^Fi.*/5/gI;s/^Si.*/6/gI;s/^Se.*/7/gI;s/^E.*/8/gI;s/^n.*/9/gI;s/^te.*/10/gI' < NumberedFiles.txt | sort | uniq | xargs -n1  -I\; find /home/ -xdev -name  \;  > search-results.txt 2> search-errors.txt &
while ps -p $! >/dev/null ; do  printf "%20s bytes and counting...\n"  $(printf "%'d" $(stat search-results.txt --printf '%s'))  ; sleep 1 ; done &
wait $!
PS="${PIPESTATUS[@]}"
echo !! > /var/run/program.cmdline
env > /var/run/program.env
echo $! > /var/run/program.pid
wait $!
echo $? > mysearch.exit
echo "Results: ${PIPESTATUS[@]}" >search-exit-codes.log





# Bonus: Match and get upper cased versions
while read NUM ; do echo "${NUM^^}" ; done<<<$(grep -iE '^z|^o|^tw|^th|^fo|^fi|^si|^se|^e|^ni|^te' < NumberedFiles.txt)