Linux shell programming : arrays
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arrays 1
Here is a simple array shell code:
#!/bin/bash
arr[0]="zero"
arr[1]="one"
arr[2]="two"
arr[3]="three"
arr[4]="four"
arr[5]="five"
echo "array size = ${#arr[*]}"
printf "array items\n"
for item in ${arr[*]}
do
printf " %s\n" $item
done
printf "array items\n"
for item in ${arr[@]}
do
printf " %s\n" $item
done
printf "array indexes\n"
for index in ${!arr[*]}
do
printf "%3d\n" $index
done
printf "index: array\n"
for index in ${!arr[*]}
do
printf "%3d: %s\n" $index ${arr[$index]}
done
Output looks like this:
$ ./array1.sh array size = 6 array items zero one two three four five array items zero one two three four five array indexes 0 1 2 3 4 5 index: array 0: zero 1: one 2: two 3: three 4: four 5: five
arrays 2
We can declare in other ways:
- Using the pair of parenthesis:
array=( element_1 element_2 element_3 ... element_n )
-
array=( [i2]=<value> [i4]=<value> ... )
-
for item in "${arr[@]}" -
for item in "${arr[*]}" - Linux Tips - links, vmstats, rsync
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- Linux shell programming : arrays - three different ways of declaring arrays & looping with $*/$@
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So, the the code below, we'll use those method of declaring arrays:
#!/bin/bash
arr1=("zero" "one" "two" "three" "four")
arr2=([4]="four" [0]="zero" [1]="one" [2]="two" [3]="three")
echo "-- without double-quot"
for item in ${arr1[@]}
do
echo $item
done
echo
for item in ${arr1[*]}
do
echo $item
done
echo
echo "-- with double-quot"
for item in "${arr2[@]}"
do
echo $item
done
echo
for item in "${arr2[*]}"
do
echo $item
done
Output:
$ ./array2.sh -- without double-quot zero one two three four zero one two three four -- with double-quot zero one two three four zero one two three four
To traverse through the array elements we used two different for loops:
As we can see from the output, the "@" sign can be used instead of the "*" in constructs such as ${arr[*]}, the result is the same except expanding the array to the items within a quoted string. In this case, the behavior is the same as when expanding "$*" and "$@" and they return all the items as a single word.
While the "${arr[@]}" returns each item as a separate word:
zero one two three four
the "${arr[*]}" returns all items in a word.
zero one two three four
arrays 3 - array sort
Generate ramdom number array with 10 elements and then sort:
#!/bin/bash
#arr=(one two three four)
arr=($(for i in {0..9};do echo $((RANDOM%100));done))
echo "initial array:"
echo "${arr[@]}"
echo "sorted array:"
echo ${arr[@]} | tr " " "\n"| sort -n | tr "\n" " "
echo
initial array: 76 7 66 15 23 7 9 78 83 93 sorted array: 7 7 9 15 23 66 76 78 83 93
Linux - system, cmds & shell
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