Handy solutions here, and being a fan of the simplicity of substitution in sed, I am especially fond of this last example by Mike.
Some folks, though, might want to insert a "_ "or a " ." where spaces occur, especially in filenames. I wrote a simple script that recursively removes spaces in a directory and in the names of its files. I find it useful for renaming my audio files.
I'll paste it below for anyone to use or modify if anyone finds it useful.
Code:
rmspaces.sh
#!/bin/ksh
#recursive script to replace spaces in filenames with periods
find . -name '* *' | while read file;
do
target=`echo "$file" | sed 's/ /\./g'`;
echo "Renaming '$file' to '$target'";
mv "$file" "$target";
done;