How to replace multiple spaces with a single space using Bash? [duplicate]

Using tr:

$ echo "too         many       spaces." | tr -s ' 'too many spaces

man tr:

-s, --squeeze-repeats       replace each sequence of a repeated character that is listed  in       the last specified SET, with a single occurrence of that charac‐       ter

Edit: Oh, by the way:

$ s="foo      bar"$ echo $sfoo bar$ echo "$s"foo      bar

Edit 2: On the performance:

$ shopt -s extglob$ s=$(for i in {1..100} ; do echo -n "word   " ; done) # 100 times: word   word   word...$ time echo "${s//+([[:blank:]])/ }" > /dev/nullreal    0m7.296suser    0m7.292ssys     0m0.000s$ time echo "$s" | tr -s ' ' >/dev/nullreal    0m0.002suser    0m0.000ssys     0m0.000s

Over 7 seconds?! How is that even possible. Well, this mini laptop is from 2014 but still. Then again:

$ time echo "${s//+( )/ }" > /dev/nullreal    0m1.198suser    0m1.192ssys     0m0.000s

Here is a way to do this using pure bash and extglob:

s="too         many       spaces."shopt -s extglobecho "${s//+([[:blank:]])/ }"

too many spaces.

• Bracket expression [[:blank:]] matches a space or tab character
• +([[:blank:]]) matches one or more of the bracket expression (requires extglob)

Another simple sed expression using BRE is:

sed 's/[ ][ ]*/ /g'

For example:

$ echo "too         many       spaces." | sed 's/[ ][ ]*/ /g'too many spaces.

There are a number of ways to skin the cat.

If the enclosed whitespace could consist of mixed spaces and tabs, then you could use:

sed 's/\s\s*/ /g'

And if you simply want to have bash word-splitting handle it, just echo your string without quotes, e.g.

$ echo "too         many       spaces." | while read line; do echo $line; donetoo many spaces.

Continuing with that same thought, if your string with spaces is already stored in a variable, you can simply use echo unquoted within command substitution to have bash remove the additional whitespace for your, e.g.

$ foo="too         many       spaces."; bar=$(echo $foo); echo "$bar"too many spaces.