How do I insert a space every four characters in a long line?

Question

I've got a long line that I want to insert a space every 4 characters, on a single lone line of solid text to make it easier to read, what's the simplest way to do this? also I should be able to input the line from a pipe. e.g.

echo "foobarbazblargblurg" | <some command here>

gives

foob arba zbla rgbl urg

Answer 1

Use sed as follows:

$ echo "foobarbazblargblurg" | sed 's/.\{4\}/& /g'
foob arba zbla rgbl urg

Answer 2

I'm going to answer by only inserting spaces as required so a space appears at least after every 4 characters on a line; not sure which way you want to handle this case. For example, given input of "aa bbccdd", you'd get output "aa bbcc dd" rather than "aa b bccd d".

I'm using Perl for lookahead, but I'm not very familiar with Perl in general, so there may be tweaks needed:

$ echo "foobarbazblargblurg" | perl -wp -e 's/[^ ]{4}(?=[^\n ])/$& /g'
foob arba zbla rgbl urg

$ echo 'aa bbccdd' | perl -wp -e 's/[^ ]{4}(?=[^\n ])/$& /g'
aa bbcc dd
# not 'aa b bccd d'!

$ echo 'some input' | perl -wp -e 's/[^ ]{4}(?=[^\n ])/$& /g'
some inpu t
# not 'some  inp ut'!

$ echo $'aabb\nc cddee' | perl -wp -e 's/[^ ]{4}(?=[^\n ])/$& /g' | 
> while read; do echo "${REPLY}x"; done
aabbx
c cdde ex
# no spaces added at the end of the first line (while loop to add to the end of
# the line and show this)