BASH - How to delete a line which contains 2nd occurrence of a pattern string using sed

Question

Consider the below configuration file and it has two instances of alt_names. Here, I want to delete a line with second occurrence of a pattern alt_names.

.
.
[ server ]
subjectAltName = @alt_names
.
.

[ alt_names ]

I tried sed command but it deletes all the lines with the pattern occurrence. I used the below command to do so,

#sed '/alt_names/{2,$d}' inputfile

Can some shed lights on whats gone wrong the usage of sed here.

P.... · Accepted Answer · 2017-06-13T07:08:54.900

1

Following will delete the second line which contains alt_names. Counter c will increase with each line having the pattern matched.

awk '/alt_names/{c++;if(c==2)gsub(/^.*$/,"")}1'
.
[ server ]
subjectAltName = @alt_names
.
.

To modify and save:

awk '/alt_names/{c++;if(c==2)gsub(/^.*$/,"")}1' inputfile >inputfile.tmp && mv inputfile.tmp inputfile

edited Jun 13 '17 at 07:08

answered Jun 13 '17 at 07:04

P....

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How to modify the file itself and save. – Panch Jun 13 '17 at 07:07
check update in answer – P.... Jun 13 '17 at 07:15
I see that, still we need to use temp file here. I though there should be something similar to what `sed` has like `sed -i filename` – Panch Jun 13 '17 at 07:19
check the dups marked by Inian, it contains some better alternatives. – P.... Jun 13 '17 at 07:20

BASH - How to delete a line which contains 2nd occurrence of a pattern string using sed

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