sed用包含嵌套引号的字符串替换行号处的整行

Question

I want to use sed to replace a certain line with my own string that has to contain some nested quotes because it will be read by another programme and itself executing commands.

sed -i '63s/^.*$/mystring/' file.txt

Where 63 is the line number, ^.*$ is selecting the entire line to replace, mystring is the replacement string and file.txt is the file to work on.

Say for example I want to make mystring exec: echo 'echo "127.0.0.1 localhost" >> /etc/hosts"' how am I supposed to go about that? I've tried escaping the quotes.

Answer 1

You can for example do the following:

sed -i.bak "63s|^.*$|$string|" file.txt

A wayis to fetch it from a file. Also, note double quotes in sed are necessary to have the variable expanded. Finally, use another delimiter for sed and store $string in a variable. For example, | . This is because your $string contain slashes and make sed see a command like sed "s/^.*$/something/blabla/" , which is so many slashes.

Also, -i.bak creates a backup of file.txt --> file.txt.bak .

Test

$ cat a
hel
lo
ooo
bye
$ cat b
exec: echo 'echo "127.0.0.1 localhost" >> /etc/hosts"'
$ string=$(cat b)

$ sed "3s|^.*$|$string|" a
hel
lo
exec: echo 'echo "127.0.0.1 localhost" >> /etc/hosts"'
bye

---

If you don't want to do variable assignment, then just escape the problematic characters in your replacement string. In this case, just double quotes " :

sed -i.bak "63s|^.*$|exec: echo 'echo \"127.0.0.1 localhost\" >> /etc/hosts\"'|" file.txt
                                      ^                    ^               ^

Test

$ sed "3s|^.*$|exec: echo 'echo \"127.0.0.1 localhost\" >> /etc/hosts\"'|" a
hel
lo
exec: echo 'echo "127.0.0.1 localhost" >> /etc/hosts"'
bye

Answer 2

This might work for you (GNU sed & Bash):

cat <<\! >quoted-text.txt
exec: echo 'echo "127.0.0.1 localhost" >> /etc/hosts"'
!

sed $'63{r quoted-text.txt\nd}' file

Put the difficult line of text into a file and replace the required line by reading said file and deleting the original line.

Answer 3

You could try this also,

sed -i "63s~.*~exec: echo \'echo \"127.0.0.1 localhost\" >> /etc/hosts\"\'~g" file

It just need escaping of quotes and a different sed delimiter.

*Example:

$ sed "2s~.*~exec: echo \'echo \"127.0.0.1 localhost\" >> /etc/hosts\"\'~g" file
abc, xym krg plf, 763, bla
exec: echo 'echo "127.0.0.1 localhost" >> /etc/hosts"'