求Linux下sed命令：替换.env中指定DB_USERNAME类变量值为root

Got it, let's solve this specific problem where you need to update only the .env variables that start with DB and end with _USERNAME, setting their values to root—leaving all other variables untouched.

The Sed Command #

Here's the exact command you can run in your Linux environment:

sed -i 's/^\(DB.*_USERNAME\)=.*/\1=root/' .env

Breakdown of the Command #

Let's break down what each part does so you understand why it works:

• -i: This flag tells sed to edit the .env file in-place (no need to redirect output to a new file; it modifies the original directly).
• ^\(DB.*_USERNAME\): The ^ anchors the match to the start of the line. The parentheses \( ... \) capture the variable name (anything starting with DB and ending with _USERNAME) so we can reuse it later.
• =.*: Matches the equal sign followed by any existing value (the .* means zero or more of any character).
• \1=root: \1 refers to the captured variable name from earlier, so we keep the original variable name and set its value to root.

Example Before/After #

If your .env had these lines:

DB_USERNAME=my_old_user
DB_ABC_DEF_USERNAME=another_user
DB_HOST=127.0.0.1
API_KEY=xyz123

After running the command, it will look like this:

DB_USERNAME=root
DB_ABC_DEF_USERNAME=root
DB_HOST=127.0.0.1
API_KEY=xyz123

Note for macOS Users #

If you're on macOS (which uses BSD sed instead of GNU sed), you need to add an empty string after -i to avoid creating a backup file by default:

sed -i '' 's/^\(DB.*_USERNAME\)=.*/\1=root/' .env

内容的提问来源于stack exchange，提问作者Fan