More On BASH Variable

General Assignment and Declaration

[bob in ~] VARIABLE=12

[bob in ~] echo $VARIABLE
12

[bob in ~] VARIABLE=string

[bob in ~] echo $VARIABLE
string

Using a declare statement, we can limit the value assign to variables.

[bob in ~] declare -i VARIABLE=12

[bob in ~] VARIABLE=string

[bob in ~] echo $VARIABLE
0

[bob in ~] declare -p VARIABLE
declare -i VARIABLE="0"

Constant

[bob in ~] readonly TUX=penguinpower

[bob in ~] TUX=Mickeysoft
bash: TUX: readonly variable

Array Variables 

Access the Values of the Array

bob in ~] ARRAY=(one two three)

[bob in ~] echo ${ARRAY[*]}
one two three

[bob in ~] echo $ARRAY[*]
one[*]

[bob in ~] echo ${ARRAY[2]}
three

[bob in ~] ARRAY[3]=four

[bob in ~] echo ${ARRAY[*]}
one two three four

[bob in ~] echo ${ARRAY[@]}
one two three four

Deleting Array

[bob in ~] unset ARRAY[1]

[bob in ~] echo ${ARRAY[*]}
one three four

[bob in ~] unset ARRAY

[bob in ~] echo ${ARRAY[*]}
<--no output-->
 

Length of Array

[root@localhost ~]# ary1=(a b c d)
[root@localhost ~]# echo ${#ary1[@]}
4
[root@localhost ~]# ary1[4]=e
[root@localhost ~]# echo ${ary1[@]}
a b c d e
[root@localhost ~]# echo ${#ary1[@]}
5

Looping through the Array

Put the content of a file in an array

a=( $( cat /tmp/ReqUrl.txt ) );
for i in ${a[@]};
do
echo ${i}
done

Loop the array item by item in a for loop

for (( k = 0 ;k < ${#a1[@]} ; k++ ))
do
echo ${a1[$k]} ${a2[$k]} `timediff ${a1[$k]} ${a2[$k]}`
done

Loop until we find an empty string 

count=0
while [ "x${wholist[count]}" != "x" ]
do
   count=$(( $count + 1 ))
done