add dot between known string and unknown string with sed

Question

Ok, so I know there is a similar post that I referred to already but does not fit the exact issue I am having.

For reference: shell sed - substitute an unknown string between a known string and a generic delimiter replace a unknown string between two known strings with sed

file unknown-string,unknown-string,unknown-string

i need to add . to be like that:

file unknown-string,.unknown-string,.unknown-string

i tried sed -i 's/file.*,/file ,./g' file.txt not working!

NOTE: there are many , in the file so i can't use sed -i 's/,/,./'

Thanks.

@DavidC.Rankin, sorry i forget something, I added NOTE to the question, that NOTE: there are many , in the file so i can't use sed -i 's/,/,./g' — test test, Aug 18 '20 at 03:21
Okay, that presents a problem. If you don't know what the text is and you can't key off the delimiters because you only want append a `'.'` after some of the delimiters -- that's not much to go on. Do you only want to append the `'.'` after the first and second commas? — David C. Rankin, Aug 18 '20 at 03:23
Or `sed -e 's/,/,./1' -e 's/,/,./2'` or just `sed 's/,/,./1;s/,/,./2'` (same thing) — David C. Rankin, Aug 18 '20 at 03:29
@Sundeep @DavidC.Rankin, As i said there are many of `,` in the file, if i tried to use your command, that will add dot to all `,` in the file, i want in this line and others like it when the `file` is known string and `unknown-string,` , i hope you understand me. — test test, Aug 18 '20 at 03:34
`sed '/^file/s/,/,./1;s/,/,./2'` That will only place a `'.'` after the first two commas in lines that begin with `"file ..."` — David C. Rankin, Aug 18 '20 at 03:43
@DavidC.Rankin, it's working, but the result is `file unknown-string,unknown-string,.unknown-string` you miss `.` after the first `,` — test test, Aug 18 '20 at 03:47
I'm a bit confused, testing with `"file unknown-string,unknown-string,unknown-string,unknown-string"` results in `"file unknown-string,.unknown-string,.unknown-string,unknown-string"` -- I thought you only wanted the `'.'` after the first two commas? (make sure you are using the revised version with `.../1.../2` not `.../2 .../3`) — David C. Rankin, Aug 18 '20 at 03:49
@DavidC.Rankin, Yes,i want `.` after the first two commas, but you miss the first comma! — test test, Aug 18 '20 at 03:50
When i run your command the result will be: ```file unknown-string,unknown-string,.unknown-string``` — test test, Aug 18 '20 at 03:52
@DavidC.Rankin, Sorry i missing something, now it's working, thank you very much for your help :) — test test, Aug 18 '20 at 03:55
@DavidC.Rankin, If you can please post an answer so i can accept it and close this question? — test test, Aug 18 '20 at 04:01

score 2 · Accepted Answer · answered Aug 18 '20 at 06:20

After some difficulty understanding the format you were trying to match, to match a line format of:

file a,b,c,d....

and append a period '.' after the first two commas only for line beginning with file, you can use a sed expression of:

sed '/^file/s/,/,./1;s/,/,./2'

Explanation

/^file/ matches only lines beginning with the word "file",
s/,/,./1 is the general substitution form where the find expression matches a comma ',' and replaces it with ",." with the 1 ending the substitution specifying that the first-occurrence of the match is to be substituted,
s/,/,./2 is the same but with 2 specifying that the second-occurrence of the match be replaced.

Example Use/Output

Continuing with the format above, you could do:

$ echo "file a,b,c,d...." | sed '/^file/s/,/,./1;s/,/,./2'
file a,.b,.c,d....

Let me know if you have any further questions.

add dot between known string and unknown string with sed

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