sed: Ignore whitespace while matching a pattern

Suppose you have a set of words or line which want to match and perform some activity but you do not know the no of whitespace between each word or string.

For eg I have a file /tmp/file with below content
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuset
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpu
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuacct
I would like to grep for "Initializing cgroup subsys cpuset"
but I do not want to risk the grep with the spaces between every word

If I do a normal search and replace like below
# sed 's/Initializing cgroup subsys cpuset/NEW CONTENT/g' /tmp/file
Dec 14 13:29:13 cc01-pgd-002a kernel: NEW CONTENT
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpu
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuacct





It worked as expected but what if there were some extra spaces between the words like below
# cat /tmp/file
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing   cgroup subsys   cpuset
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpu
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuacct
and trying the same command as above
# sed 's/Initializing cgroup subsys cpuset/NEW CONTENT/g' /tmp/file
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing   cgroup subsys   cpuset
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpu
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuacct
It didn't worked.

So we have to try to ignore these whitespaces so that we have a perfect match
# sed 's/Initializing\s*cgroup\s*subsys\s*cpuset/NEW CONTENT/g' /tmp/file
Dec 14 13:29:13 cc01-pgd-002a kernel: NEW CONTENT
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpu
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuacct
It worked so below is what you have to use
\s   This is equivalent to [[:blank:]]
*    means 0 or higher
So search for all whitespace (0 or higher) when used
# sed 's/Initializing[[:blank:]]*cgroup[[:blank:]]*subsys[[:blank:]]*cpuset/NEW CONTENT/g' /tmp/file
Dec 14 13:29:13 cc01-pgd-002a kernel: NEW CONTENT
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpu
Dec 14 13:29:13 cc01-pgd-002a kernel: Initializing cgroup subsys cpuacct

Follow the below links for more tutorials

10 Basic examples of SED to perform per line action (print/delete)
sed: perform search and replace only on specific lines (not globally)
sed: delete all blank lines from a text file
sed: case insensitive actions (search replace delete..)
sed: remove all leading and ending blank whitespace from a file
sed :Replace whole line when match found
sed: Replace string based on line number (certain line)
sed: Insert multiple lines before or after pattern match
sed: match string and append new line (before or after)
How to add line number at the beginning of each line
sed: Insert character in the beginning or end of line with matched pattern
sed: insert word after match in middle of the line