Shell Programming and Scripting

Consider a directory containing the following files:

Code:

-rwxr-xr-x  1 dwc  staff  1361 Jun 25 13:06 Scrutinizer
-rw-r--r--  1 dwc  staff     0 Jun 25 14:14 a b
-rwxr-xr-x  1 dwc  staff   326 Jun 25 14:12 tester

And assume that tester contains the script:

Code:

#!/bin/bash
array=( * )
printf 'There are %d elements in array.\n' ${#array[@]}
for((i = 0; i < ${#array[@]}; i++))
do	printf 'array[%d]:"%s"\n' $i "${array[i]}"
done
array=( $(ls) )
printf 'There are %d elements in array.\n' ${#array[@]}
for((i = 0; i < ${#array[@]}; i++))
do	printf 'array[%d]:"%s"\n' $i "${array[i]}"
done

And note the difference in the output produced by running ./tester when * and $(ls) are used to initialize the array, respectively:

Code:

There are 3 elements in array.
array[0]:"Scrutinizer"
array[1]:"a b"
array[2]:"tester"
There are 4 elements in array.
array[0]:"Scrutinizer"
array[1]:"a"
array[2]:"b"
array[3]:"tester"

Adding a command substitution to the array initializer makes the shell lose track of filename boundaries.

The ls command with no arguments is great as an interactive tool. In a shell script, it is seldom needed and occasionally leads to the wrong results.

Point taken - thank you!

Thanks for all your responses, they were really helpful!

I was also hoping to run this kind of a command in the array:

Code:

for i in `ls -d */  ; do (cd $i; echo $i && ls);done

What this does is it cds to all of the directories and then prints out the files within them.

Is this also possible using the array created that contains all the directories? I have been unable to get the array to perform what the above command does.

First, note that the command substitution marked in red above is incomplete (no closing quote). Second, there is no need for a command substitution there at all. Third, unless you are doing this in a directory where you know beforehand that there is no possibility of whitespace characters or characters that are special in a filename matching pattern in a directory name, you need to quote your uses of the loop variable. And, finally unless you know that there aren't any backslash characters in your directory names and that none of them start with a hyphen, printf is safer than echo. So, I would change the above code to:

Code:

for i in */; do (cd "$i"; printf '%s\n' "$i" && ls);done

And, if you have an array of directories to process, try:

Code:

dirs=( */ )
for i in "${dirs[@]}"; do (cd "$i"; printf '%s\n' "$i" && ls);done

If I was writing this for my personal use, I'd probably change the printf format string to '\n%s\n' to add a little visual separation between directory listings. But, since I don't mind also have a colon added to the ends of the lines denoting directories, I would replace these loops with:

Code:

ls */
 and
dirs=( */ )
ls "${dirs[@]}"

respectively.