• The special variable ? has the exit/return value of the last program/command that ran.

if [ $? -eq 0 ]; then
    echo "All is well."
    exit 0
elif [ $? -eq 1 ]; then 
    echo "Doh!"
    exit 1
else
   echo "Really?!"
   exit 2
fi

if [$? -eq 0]; then echo "OK"; else echo "Error"; fi

for i in alpha beta gamma
do
    printf "$i\n"
done
 
a=alpha
b=beta
c=gamma
 
for j in "$a" "$b" "$c"; do
    printf "$j\n"
done

for i in $( ls ); do
  echo item: $i
done
 
LIST="$(ls *.html)"
for i in "$LIST"; do
   echo $1
done

===while loop===COUNTER=0

while [  $COUNTER -lt 10 ]; do
  echo The counter is $COUNTER
  let COUNTER=COUNTER+1 
done