How to use sed 's/$var/$var2' file

Question

I'm trying to replace a value shown as a variable with another value shown as a second variable, using the following line:

    sed -i "s/$header/$new/" file.f

Where "$header" is the old variable I want replaced with the new one ($new).

I'm getting this error:

    sed: -e expression #1, char 20: unknown option to `s'

I've tried

    sed -i 's/$header/$new/' file.f
    sed -i "s/$header/$new/" file.f
    sed -i 's/"$header"/"$new"/' file.f

None of it seem to work. How should I write this line so I can get the right output (replacing '$header' with '$new' on the file)?

Thanks in advance

As lurker mentioned, use `sed 's/\$header/\$new/'`. Also on a side note, O suggest to first test the `sed` command without `-i` and verify the output on screen. Once you are sure that it is working the way you expected, add `-i`. — Utsav, May 30 '17 at 17:23
@lurker the variables are expanded before sed even starts, so that doesn't matter at all. — 123, May 30 '17 at 17:29
@Utsav I have no idea what you think your suggested code will do. — 123, May 30 '17 at 17:29
I tried your way and it works. Can you share what is your $header and $new? — Hungry Mind, May 30 '17 at 17:30
@op, you'll have to show us the contents of the variables but at a guess they contain `/` and you will need a different delimiter. — 123, May 30 '17 at 17:31
Do you want to replace literally `$header` with `$new`, or the values of variables called `header` and `new`? — Benjamin W., May 30 '17 at 17:31
@123 - It would change $header with $new literally, which I think is what OP is trying to ask. — Utsav, May 30 '17 at 17:33
@Utsav the title says variables and the first thing they tried `sed -i 's/$header/$new/'` would have worked if that were the case. You would only need to escape `$` if it were the last char. — 123, May 30 '17 at 17:35

Baroudi Safwen · Accepted Answer · 2017-05-30T20:48:30.287

0

sed -i "s/$old/$new/" file

works fine. You can change the separtor if your data has the character /.

sed -i "s@$old@$new@" file

edited May 30 '17 at 20:48

answered May 30 '17 at 17:39

Baroudi Safwen

Try with `$old=foo/bar` value! – uzsolt May 30 '17 at 17:46
Try sed "s@$old@$new" file – Baroudi Safwen May 30 '17 at 17:57
1

You should also realize that any regex special characters in `$old` (the pattern) need to be escaped and in the replacement `$new` the back slash is special in needs to be escaped. – fd0 May 30 '17 at 18:08
`"s@$old@$new@"`, with the trailing `@`. and what @fd0 just said about escaping. – ilkkachu May 30 '17 at 19:02

score 0 · Answer 2 · answered May 30 '17 at 18:10

0

If you are not sure of the content of the variables and to reduce clashing the separator you can use

sed "s^A$old^A$new^A"

to enter the CTRL-A press CTRL-V + CTRL-A (or any other value not expected in vars)

answered May 30 '17 at 18:10

2 Answers2