How do I use bash for loop to iterate thought array values under UNIX / Linux operating systems?
The Bash provides one-dimensional array variables. Any variable may be used as an array; the declare builtin will explicitly declare an array. There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Arrays are indexed using integers and are zero-based.
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To declare an array in bash
Declare and an array called array and assign three values:
array=( one two three ) |
More examples:
files=( "/etc/passwd" "/etc/group" "/etc/hosts" ) limits=( 10, 20, 26, 39, 48) |
To print an array use:
printf "%s\n" "${array[@]}" printf "%s\n" "${files[@]}" printf "%s\n" "${limits[@]}" |
To Iterate Through Array Values
Use for loop syntax as follows:
for i in "${arrayName[@]}" do : # do whatever on $i done |
$i will hold each item in an array. Here is a sample working script:
#!/bin/bash # declare an array called array and define 3 vales array=( one two three ) for i in "${array[@]}" do echo $i done |
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Defining the array with double parentheses gave me an error. Using single parentheses did not and worked just fine. This tip mixes them, showing double parentheses at the top, but then using single parentheses in the for loop.
HI
Want to know , how to create a Two dimension array in bash and print all in one go.
eg like in one dimension array,
echo ${array[@]}
What for two dimension array ??
Thanks in advance…
The double quotes are not necessary around ${array[@]}. This expression gets evaluated properly anyway.
Not true, without the quotes you’ll have errors with elements with spaces. Try:
$ arr=("a 1" "b" "c") $ for i in "${arr[@]}"; do echo $i; done a 1 b c $ for i in ${arr[@]}; do echo $i; done a 1 b cist there a nice way of doin this backwards? at the moment im writing something like this:
for ((i=${#ARRAY[@]}; i > 0; i–)); do echo ${ARRAY[$i]}; done
http://www.linuxjournal.com/content/bash-arrays
${arr[*]} # All of the items in the array
${!arr[*]} # All of the indexes in the array
${#arr[*]} # Number of items in the array
${#arr[0]} # Length of item zero
for index in ${!array[*]}
do
printf “%4d: %s\n” $index ${array[$index]}
done
I tried looping through a directory of approx 80 files. I looped trough them and placed them into an Array. Then I did a nested loop through the array to find duplicated (case insensitive) dir names.
But this is just as slow as looping straight through the dirs using For x in ./*..
Can someone with explain this?
A loop is a loop. It is slow.
It doesn’t matter whether you are looping through array elements or filenames, it’s the same thing.
Assigning filenames to an array is fast if you can use pathname expansion:
Merely printing elements of an array doesn’t require a loop:
printf "%s\n" "${textfiles[@]}" ## yes, the double quotes ARE necessaryNot true, you can actually still use single quotes.
printf ‘%s\n’ ‘ ‘${textfiles[@]}’ ‘
You just have to wrap the variable you’re putting in there in single quotes as well if you choose to use them.
good example.
Thank you, I’m a bash noob and this helped me understand loops.
Maybe you can help me with a challenge I am facing … I am trying to build a script to rsync certain files to a portable drive, and I want to use loop to iterate through file names, each on a new line in the script. The files are all in the same source directory, so I would just like to list the file names of the movies I want on a new line, and have the script copy each to the destination. For example:
Movie Title 1.mkv
Another Movie.mkv
Some Other Title.mkv
Is there a way I can define an array like that? How do I handle spaces in the file names?
Hi bashnoob..
Just use a for loop.
May be try this.. but it depends on the version of the bash you are using..
You can use folder1 and folder2 in a for loop to check the file system.. it would recognize the spaces and work accordingly with this.
ls -lh “/$folder1/\”$folder11\””