Hi all, 
I have fastQ file and I need to rename it using `sed` command.  below the explanation :

The read names in my files are

```
@HWI-ST365:251:D0RP0ACXX:5:1101:4471:2213#12_1
@HWI-ST365:251:D0RP0ACXX:5:1101:4471:2213#12_2
```
And i want to transform them in the format:

```
@HWI-ST365:251:D0RP0ACXX:5:1101:4471:2213#12/1
@HWI-ST365:251:D0RP0ACXX:5:1101:4471:2213#12/2
```
Thank you very much in advance for your help.

Well, you're very close to the solution. You only need to scape to '`/`' character: `sed -i 's/_/\//g'` should work.

Just a little advice, try to call to sed command in the following way:

    cat file.fq | sed 's/_/\//g' > reformat.fq

In this way you can go back to the original input file in the case that something has gone wrong. In my opinion it is a good practice.