How to split one string into multiple strings separated by at least one space in bash shell?

Question

I have a string containing many words with at least one space between each two. How can I split the string into individual words so I can loop through them?

The stri

Answer 1

Probably the easiest and most secure way in BASH 3 and above is:

var="string    to  split"
read -ra arr <<<"$var"

(where arr is the array which takes the split parts of the string) or, if there might be newlines in the input and you want more than just the first line:

var="string    to  split"
read -ra arr -d '' <<<"$var"

(please note the space in -d ''; it cannot be omitted), but this might give you an unexpected newline from <<<"$var" (as this implicitly adds an LF at the end).

Example:

touch NOPE
var="* a  *"
read -ra arr <<<"$var"
for a in "${arr[@]}"; do echo "[$a]"; done

Outputs the expected

[*]
[a]
[*]

as this solution (in contrast to all previous solutions here) is not prone to unexpected and often uncontrollable shell globbing.

Also this gives you the full power of IFS as you probably want:

Example:

IFS=: read -ra arr < <(grep "^$USER:" /etc/passwd)
for a in "${arr[@]}"; do echo "[$a]"; done

Outputs something like:

[tino]
[x]
[1000]
[1000]
[Valentin Hilbig]
[/home/tino]
[/bin/bash]

As you can see, spaces can be preserved this way, too:

IFS=: read -ra arr <<<' split  :   this    '
for a in "${arr[@]}"; do echo "[$a]"; done

outputs

[ split  ]
[   this    ]

Please note that the handling of IFS in BASH is a subject on its own, so do your tests; some interesting topics on this:

• unset IFS: Ignores runs of SPC, TAB, NL and on line starts and ends
• IFS='': No field separation, just reads everything
• IFS=' ': Runs of SPC (and SPC only)

Some last examples:

var=$'\n\nthis is\n\n\na test\n\n'
IFS=$'\n' read -ra arr -d '' <<<"$var"
i=0; for a in "${arr[@]}"; do let i++; echo "$i [$a]"; done

outputs

1 [this is]
2 [a test]

while

unset IFS
var=$'\n\nthis is\n\n\na test\n\n'
read -ra arr -d '' <<<"$var"
i=0; for a in "${arr[@]}"; do let i++; echo "$i [$a]"; done

outputs

1 [this]
2 [is]
3 [a]
4 [test]

BTW:

• If you are not used to $'ANSI-ESCAPED-STRING' get used to it; it's a timesaver.

• If you do not include -r (like in read -a arr <<<"$var") then read does backslash escapes. This is left as exercise for the reader.

---

For the second question:

To test for something in a string I usually stick to case, as this can check for multiple cases at once (note: case only executes the first match, if you need fallthrough use multiple case statements), and this need is quite often the case (pun intended):

case "$var" in
'')                empty_var;;                # variable is empty
*' '*)             have_space "$var";;        # have SPC
*[[:space:]]*)     have_whitespace "$var";;   # have whitespaces like TAB
*[^-+.,A-Za-z0-9]*) have_nonalnum "$var";;    # non-alphanum-chars found
*[-+.,]*)          have_punctuation "$var";;  # some punctuation chars found
*)                 default_case "$var";;      # if all above does not match
esac

So you can set the return value to check for SPC like this:

case "$var" in (*' '*) true;; (*) false;; esac

Why case? Because it usually is a bit more readable than regex sequences, and thanks to Shell metacharacters it handles 99% of all needs very well.