用不同字节的熵替换文件中出现的字符串

Question

On Linux, I need to programmatically replace placeholder strings such as <SECRET> in a .env file like this:

KEY=<SECRET>
ANOTHER_VARIABLE=another-value
# here's a comment
PASSWORD=<SECRET>

The caveat is, that each occurrence of this placeholder must be replaced with a different instantiation of Base64 encoded randomness - eg from OpenSSL, since it's readily available on many Linuxes.

Reading this answer , I tried this with GNU sed 4.8:

sed -i '0,/<SECRET>/ s__'$(openssl rand -base64 42)'_' .env

(In the substitution part the alternative delimiter _ was chosen, because the Base64 encoded bytes can contain / or + characters and would otherwise clash when inadvertently used as delimiters.)

---

This works for single replacements, one call at a time.

But sed's return code is always 0 , even when all occurrences of the regex have been consumed and replaced...

Question: Is there a way to make sed return a non-zero code when placeholders have been exhausted?

(If this can't be done with sed, I'm happy for any solution with awk or similar.)

Answer 1

Instead of sed , you could use grep :

grep '<SECRET>' .env

From man grep :

EXIT STATUS

Normally the exit status is 0 if a line is selected, 1 if no lines were selected, and 2 if an error occurred. However, if the -q or --quiet or --silent is used and a line is selected, the exit status is 0 even if an error occurred.

If the return value is 0, then apply your sed command to perform the substitution.

Answer 2

$ awk '
    BEGIN { cmd = "openssl rand -base64 42" }
    match($0,/<SECRET>/) {
        val = ( (cmd | getline line) > 0 ? line : "N/A" )
        $0 = substr($0,1,RSTART-1) val substr($0,RSTART+RLENGTH)
        close(cmd)
    }
1' file
KEY=hDc3Bw4J9+TUbbhw4cNKda+mDHVRGGrAWUU6LX7aYZnWwDZWyqrmzi3z
ANOTHER_VARIABLE=another-value
# here's a comment
PASSWORD=LzGaB43Mm5mF6tsJnwOLqgeeoTwajH9FNLty9yD22QovadhwWKpr7AP6

or if <SECRET> can occur multiple times on 1 line then:

$ awk '
    BEGIN { cmd = "openssl rand -base64 42" }
    {
        while ( match($0,/<SECRET>/) ) {
            val = ( (cmd | getline line) > 0 ? line : "N/A" )
            $0 = substr($0,1,RSTART-1) val substr($0,RSTART+RLENGTH)
            close(cmd)
        }
    }
1' file
KEY=t3/bimGkyPQcjOL6ubV6QmRnPjrvtg4+HvvkuJSnuYCYc+BzOmAWKRV6
ANOTHER_VARIABLE=another-value
# here's a comment
PASSWORD=TKvDbMphOhmhL0/NSQEE2Gs9sFr3Cwt9o3CbOoe9FZPjAR/+m6i4QjcR