How to check string contain multiple tabs or spaces?

UNIX for Beginners Q & A
1

str contains tabs and multiple spaces

str="hello                       world. How are    you?"

I want to check string start with hello world,
and my code is:

if [[ $str == "hello[[:blank:]]world"* ]]; then
  echo "found"
else
  echo "not found"
fi

Not work

Other solution may work is to replace all tabs and spaces with a single space. I googling and found a solution

	shopt -s extglob
	temp=$(echo "${str//+([[:blank:]])/ }")
	if [[ $temp == "hello world"* ]]; then
		echo "found"
	fi

But I don't want to replace, just check in condition. I am new to shell, sorry.

2

Hi, maybe this will help?

if [[ $(echo $str) == "hello world"* ]];
3 Likes
3

That's clever. By feeding it into a command without quotes, you've flattened the whitespace.

2 Likes
4

You seem to have a sufficiently recent shell... man bash :

Thus, try also

if [[ $str =~ "^hello[[:blank:]]*world" ]];
1 Like
5

Then already

if [[ "$str" =~ ^"hello"[[:blank:]]+"world" ]];

--- Post updated at 23:57 ---

or

if [[ "$str" =~ ^hello[[:blank:]]+world ]];

--- Post updated 03-21-19 at 00:04 ---

Actually this is news to me. It's regexp. Even have to escape question mark

if [[ "$str" =~ ^hello[[:blank:]]+world.*\?$ ]];