How to Remove Lines Starting with a Pattern from a File in Linux

Sometimes, when working with log files, backups, or system-generated data, you may want to delete lines that begin with a specific pattern. Luckily, Linux provides several quick and powerful ways to do this from the command line.

In this article, we’ll explore how to remove lines that start with a certain prefix or string using tools like sed and egrep. These methods are efficient and work well for automation or scripting.

Use Case Example

Let’s say you have a log file with a list of changed files, and you want to remove all lines that start with ./var/cache, which typically includes cached files that don’t need to be tracked in backups or version control.

🔧 Method 1: Using `sed`

The sed (stream editor) tool is very powerful for text processing. You can delete lines that match a certain pattern using the d command.

sed '/^\.\/var\/cache/d' /home/taras/website_backups/changed_files.log > /home/taras/website_backups/changed_files_cleaned.log

Explanation:

^\.\/var\/cache — Matches lines starting with ./var/cache
d — Deletes the matched lines
The output is redirected to a new cleaned file

✅ Tip: Always test sed commands on a copy of your file to avoid accidental data loss.

🧰 Method 2: Using `egrep` (or `grep -E`)

Another simple and readable method is to use egrep or grep -E with the -v (invert match) option, which excludes matching lines.

egrep -v '^\.\/var\/cache' /home/taras/website_backups/changed_files.log > /home/taras/website_backups/changed_files_cleaned2.log

Or using grep -E:

grep -Ev '^\.\/var\/cache' /home/taras/website_backups/changed_files.log > /home/taras/website_backups/changed_files_cleaned2.log

🔍 How to Verify the Results

You can compare the original and the cleaned file using the diff command:

diff /home/taras/website_backups/changed_files.log /home/taras/website_backups/changed_files_cleaned.log

diff /home/taras/website_backups/changed_files.log /home/taras/website_backups/changed_files_cleaned2.log

This will show you exactly what lines were removed.

🧪 More Practical Examples

Remove comment lines starting with `#`:

sed '/^#/d' config.txt > config_cleaned.txt

Remove empty lines:

sed '/^$/d' notes.txt > notes_no_empty.txt

Remove all lines starting with "DEBUG" in a log:

grep -v '^DEBUG' app.log > app_cleaned.log

🛡️ Pro Tip: In-place Editing with `sed`

If you want to edit the file directly (be careful!):

sed -i '/^\.\/var\/cache/d' /home/taras/website_backups/changed_files.log

The -i flag tells sed to edit the file in place.

🧠 Conclusion

Whether you’re cleaning up logs, filtering backups, or preprocessing data for scripts, these simple command-line tricks with sed and grep can save you time and effort.

If you’re working with Linux regularly, mastering these tools is a must. They’re versatile, fast, and script-friendly.

📣 Share Your Use Case

Have you used similar commands in your daily work? Share your examples in the comments or drop me a message—I’d love to include more community-driven use cases in future posts!

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