selectively remove blank spaces from string
I'm a newbie to shell scripting and I have the following problem:
I need all spaces between two letters or a letter and a number exchanged for an underscore, but all spaces between a letter and other characters need to remain.
One example for clarity:
force -- lamin 90 [label]
active A -- generation [label]
force -- lamin_90 [label]
active_A -- generation [label]
I tried solving this with sed but obviously s/ /_/g does not work, nor does any s/[a-zA-z0-9] [a-zA-z0-9]/[a-zA-z0-9]_[a-zA-z0-9]/g , because you just can't do this...
Can anyone help me?
Thanks in advance!