Tips/Shell Script Notes

Shell Script Notes

Using `expr`

 NUM=6.6
 VAL=`expr $NUM \> 5`
 echo "VAL is $VAL"  # returns 1

 VAL=`expr $NUM \< 5`
 echo "VAL is $VAL"  # returns 0

Do something if files don't exist

 if [ ! -f foob* ]; then
   echo "no foob* files exist"
 fi

Infinite loop

 while :
 do
   echo -n "still going... "
   date
   sleep 1
 done

Count elements in a variable

 PACKAGES="one two three"
 NUM_PACKAGES=`echo ${PACAKGES} | wc -w | awk '{print $1}'`
 echo "There are $NUM_PACKAGES packages to install for this system"

passing parameters to subroutines

 do_something() {
   count=0
   #num_args=$#
   num_args=`echo ${*} | wc -w | awk '{print $1}'`

   echo "I just recieved $num_args args"
   echo "The first variable just passed to me: $1"
   echo "This was just passed to me: $*"
   for arg in $*; do
     count=`expr $count + 1`
     echo "arg $count: $arg"
   done
 }

 VAR="1 2 3"
 do_something $VAR

Variable test

 if [ ${1}x = 'x' ]; then
   echo "You must include a valid environment abbreviation:"
   echo "   $0 sapbw"
   echo "   $0 bi"
   exit 1
 fi

A simple for loop

 LOOP="1 2 3 4"
 I=1
 for ITEM in ${LOOP}; do
   echo $ITEM:$I
   I=`expr $I + 1`
 done