Ways to Replace Multiple Spaces in Text (Awk,Sed,tr)

The awk way:  

$ cat file.txt | awk '{gsub("[ ]+"," ");print}' 

The tr way:

$ cat file.txt | tr -s " " 

where -s stands for squeeze and can be used on any character not only spaces

The sed way: 

$ cat file | sed -r 's/[ ]+/ /g'