Bash 替换 tail -f 后的前 4 个字符

Question

I have a log-file as.txt where I want the first four characters to be replaced by **** or XXXX to anonymize the data.

I am running the following command:

tail -f file.txt

I know I can cut the first characters the following way:

tail -f file.txt | cut -c4-

But I would then like to insert four wildcard characters.

How can I achieve this?

Answer 1

echo 1234567890 | sed 's/..../****/'

Output:

****567890

Answer 2

To tail the file continuously with the first four characters anonymized, you can use the following command:

tail -f file.txt | sed 's/^..../****/'

If you have a file that's done being written to and you want to anonymize all the data in it at once, you can use sed as follows:

sed -i 's/^..../****/g' 58486880.txt

Note that this second command works with GNU/Linux sed, but not BSD/MacOS sed.

Answer 3

Because the question and title do not match, to replace the last four you have to use $ as such:

tail -f tmp.txt | sed 's/.\{4\}$/****/'

To test:

 while true; do cat <(seq 1 10 | tr -d '\n') <(echo) >> tmp.txt; sleep 1; done

This produces:

1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****
1234567****