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
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
It worked as expected but what if there were some extra spaces between the words like below
and trying the same command as above
It didn't worked.
So we have to try to ignore these whitespaces so that we have a perfect match
It worked so below is what you have to use
So search for all whitespace (0 or higher) when used
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 cpuacctI 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 cpuacctIt 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 cpuacctand 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 cpuacctIt 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 cpuacctIt worked so below is what you have to use
\s This is equivalent to [[:blank:]]
* means 0 or higherSo 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 cpuacctFollow the below links for more tutorials
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sed: Insert character in the beginning or end of line with matched pattern
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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