Removing leading, trailing and multiple spaces within a string

Question

I would like to remove all leading and trailing spaces. As well as replace multiple spaces with a single space within a string, so that all words in a string are separated exactly by single space.

I could achieve this using following two iteration of regex and looking for single regex solution.

s/^\s+|\s+$//g
s/\s+/ /g

Sample Input:

   word1   word2 word3     word4    

Desired Output:

word1 word2 word3 word4

It would be appreciable if you could help me to solve this.

Answer 1

You can use something like:

s/^\s+|\s+$|\s+(?=\s)//g

\s+(?=\s) will match all the spaces in the middle of the string and leave one.

Answer 2

In Javascript, the string prototype has two methods that can manage this:

str = str.trim().replace(/\s+/g, ' ')

str.trim() — removes leading and trailing spaces (and returns a new string without modifying the original)

str.replace(regex, replacement) — compares regex against the provided string, replaces matched instances with replacement, then returns the result as a new string.

In my example, the regex is delimited with slashes (/regex/) and then g is appended, indicating we want to globally replace every matched instance. Without that 'g' flag, it will to just replace the first match.

Note: The first argument of .replace() should not be encapsulated with quotes if you want it to be interpreted as a regular expression.

\s+ matches multiple spaces in a row

example:

let singleSpace = (sloppyStr) => { 
    let cleanStr = sloppyStr.trim().replace(/\s+/g, ' ');
    console.log(cleanStr)
}

singleSpace('   1 2  3   4 ')

yields: '1 2 3 4'

regex: kleene operators will help you understand the regex used to match multiple spaces

Learn more:

regex: helpful guide on regex and /g flag

Google: MDN string trim

Google: MDN string replace

Answer 3

Using awk

echo "   word1   word2 word3     word4  " | awk '{$1=$1}1'
word1 word2 word3 word4

This $1=$1 is a trick to concentrate everything.

You can even use

awk '$1=$1' file

But if first field is 0 or 0.0 it will fail

Answer 4

This might work for you (GNU sed):

sed -r 's/((^)\s*(\S))|((\S)\s*($))|(\s)\s*/\2\3\5\6\7/g' file

or simply:

sed -r 's/(^\s*(\S))|((\S)\s*$)|(\s)\s*/\2\4\5/g file

Answer 5

If you are on UNIX, you could take advantage of the shell's Word-splitting. Bash example using command substitution below

STR="   word1   word2 word3     word4  "
z=$(echo $STR)
echo "$z"
word1 word2 word3 word4