Linux – How to remove line if it contains a character exactly once

awklinuxsedtext processing

I want to remove a line from a file which contains a particular character only once, if it is present more than once or is not present then keep the line in file.

For example: 

DTHGTY
FGTHDC
HYTRHD
HTCCYD
JUTDYC

Here, the character which I want to remove is C so, the command should remove lines FGTHDC and JUTDYC because they have C exactly once.

How can I do this using either sed or awk?

Best Answer

In awk you can set the field separator to anything. If you set it to C, then you'll have as many fields +1 as occurrences of C.

So if you say awk -F'C' '{print NF}' <<< "C1C2C3" you get 4: CCC consists in 3 Cs, and hence 4 fields.

You want to remove lines in which C occurs exactly once. Taking this into consideration, in your case you will want to remove those lines in which there are exactly two C-fields. So just skip them:

$ awk -F'C' 'NF!=2' file
DTHGTY
HYTRHD
HTCCYD
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