Why aren't these 2 expressions equivalent in bash?

Question

I am wondering why the following 2 cases have two different outputs. I expected 2 on the second case:

localhost:~$ titles=('word1  word2' 'word1  word2')
localhost:~$ echo "${#titles[@]}"
2

localhost:~$ titles=($(echo "'word1  word2' 'word1  word2'"))
localhost:~$ echo "${#titles[@]}"
4

Answer 1

The first assignment to the array titles assigns the two strings word1  word2 and word1  word2 to the array.

The second assignment contains an unquoted command substitution. The command in the substitution outputs the single string 'word1  word2' 'word1  word2', and, since the substitution is unquoted, the shell will split this string on the characters in $IFS into words (by default, this variable contains a space, a tab, and a newline).

When the string is split into words, the words generated are 'word1, word2', 'word1 and word2' (four words). These words are then assigned as individual elements to the array titles.

This is further explained in the answers to other questions. See for example:

• Single quote within double quotes and the Bash reference manual
• When is double-quoting necessary?
• Why does my shell script choke on whitespace or other special characters?
• What is the 'IFS'?