[Shell: classic control flow (conditionals, loops)] #if #case #then #sh #while #for #if #case #switch #else

controlFlow.sh

##### if, elif, else, fi (CONDITIONAL) #####
# https://www.netacad.com/courses/os-it/ndg-linux-essentials --> Ch11: Basic Scripting
if [ "$1" = "hello" ]; then # square brackets are same as test command `test "$1" = "hello"`
  echo "hello yourself"
elif [ "$1" = "goodbye" ]; then
  echo "nice to have met you"
  echo "I hope to see you again"
else
  echo "I didn't understand that"
fi


##### case (CONDITIONAL; SWITCH) #####
# http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html
space=`df -h | awk '{print $5}' | grep % | grep -v Use | sort -n | tail -1 | cut -d "%" -f1 -`
case $space in
[1-6]*)
  Message="All is quiet."
  ;; # denote end of case section
[7-8]*)
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
  ;;
9[1-8])
  Message="Better hurry with that new disk...  One partition is $space % full."
  ;;
99)
  Message="I'm drowning here!  There's a partition at $space %!"
  ;;
*)
  Message="I seem to be running with an nonexistent amount of disk space..."
  ;;
esac
echo $Message

##### for (LOOP) #####
# loop through list of strings
SERVERS="serverA serverB serverC"
for S in $SERVERS; do
  echo "Doing something to $S" #serverA --> serverB --> serverC
done
# loop through list of files
for f in *; do
  echo "$f"
done

##### while (LOOP) #####
# loop through with test conditon
i=0
while [ $i -lt 10 ]; do
  echo $i
  (( i++ )) # increase x in place; same as `i=$(( $i + 1 ))`
done
echo “Done counting”