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I have a script that I'm currently working on. And I've run into an issue where I need to prompt a user to enter a string, then encrypt that with sha-512, and then insert it into a specific file

So far I have:

pass= grub-crypt --sha512

Which returns the hashed value I need. However, I'm running into the issue where sed will read the special characters from the hash.

I then tried:

sed -i.bak "20i$pass" /foo/bar

But that doesn't work. I assume it's still reading the special characters when it substitutes the variable for the characters in the string. So I wanted to try and add an escape character before every character in the string like this:

sed 's:\(.\{1\\}\)\1:g'

However, this isn't working for me either. I'm new to sed, so any explanation would be very helpful. Thank you.

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  • It might help if you posted some example values of $pass for which you're having problems, the exact commands that you're using, and the results that you're getting. – G-Man Says 'Reinstate Monica' Oct 9 '14 at 15:50
  • If you want to capture the output of grub-crypt, you need something like pass=$(grub-crypt --sha512) – user2313067 Oct 9 '14 at 17:01
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In cases where special characters such as * . / $ abound in text it's easiest not to use insert the text directly. The alternative is to add backslashes which is a drab manual solution.

Rather use the r sed function - which reads in the following file at the address specified (in this case line 20). Note there is no error handling in this code:

grub-crypt --sha512 > hash.tmp
sed -i.bak '20r hash.tmp /foo/bar      
rm hash.tmp  
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  • Unfortunately that did not work, either. I think it is still reading the special characters in the hash. – Afflickted Oct 9 '14 at 14:46
  • updated answer - works for me with special chars like $5ks&-£££%()-$. – suspectus Oct 9 '14 at 15:31
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    @suspectus: I think the second variant in your first version of the answer should work. Did you really mean to post a revision in which $pass is not quoted at all? – G-Man Says 'Reinstate Monica' Oct 9 '14 at 15:49
  • @G-Man agreed - the variable needs to be quoted. I don't know what I was thinking of. – suspectus Oct 9 '14 at 16:32
  • So an example of the special characters in the has are '$', '.', and '/'. Otherwise. running the following script commands #!/bin/bash pass= grub-crypt ---sha-512 sed -i.bak '20i\ '$pass'' /foo/bar It then prints the hash of the password that I enter, and inserts two blank lines(at line 20) in the file that I'm trying to insert the hash too – Afflickted Oct 9 '14 at 16:35

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