Replace whole line when match found with sed

Question

I need to replace the whole line with sed if it matches a pattern. For example if the line is 'one two six three four' and if 'six' is there, then the whole line should be replaced with 'fault'.

Answer 1

You can do it with either of these:

sed 's/.*six.*/fault/' file     # check all lines
sed '/six/s/.*/fault/' file     # matched lines -> then remove

It gets the full line containing six and replaces it with fault.

Example:

$ cat file
six
asdf
one two six
one isix
boo
$ sed 's/.*six.*/fault/'  file
fault
asdf
fault
fault
boo

It is based on this solution to Replace whole line containing a string using Sed

More generally, you can use an expression sed '/match/s/.*/replacement/' file. This will perform the sed 's/match/replacement/' expression in those lines containing match. In your case this would be:

sed '/six/s/.*/fault/' file

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What if we have 'one two six eight eleven three four' and we want to include 'eight' and 'eleven' as our "bad" words?

In this case we can use the -e for multiple conditions:

sed -e 's/.*six.*/fault/' -e 's/.*eight.*/fault/' file

and so on.

Or also:

sed '/eight/s/.*/XXXXX/; /eleven/s/.*/XXXX/' file