How to delete matching lines with sed

Deleting matching lines with sed removes unwanted records from a text stream or file without changing the surrounding rows. This is useful when a generated list, export, or log excerpt contains a known line category that should be excluded before review or handoff.

The d command deletes lines selected by a sed address. In sed '/status=remove/d' cleanup-list.txt, the address is the regular expression between the slashes, and only lines matching that expression are removed from the output.

Preview the deletion before editing a file in place. A broad pattern can remove more rows than intended, so the first check should keep the nonmatching rows visible and make the removed line category easy to recognize.

1. Prepare or inspect a file that contains both matching and nonmatching rows.

   cleanup-list.txt

   host=db-01 status=keep
   host=db-02 status=remove
   host=web-01 status=keep
   host=web-02 status=remove
   host=cache-01 status=keep

   Use a copy of an important file while testing the pattern. The examples below remove only rows containing status=remove.

2. Preview the deletion by sending the filtered output to the terminal.

   $ sed '/status=remove/d' cleanup-list.txt
   host=db-01 status=keep
   host=web-01 status=keep
   host=cache-01 status=keep

   sed treats the text between the slashes as a regular expression. Match a literal phrase when possible, or anchor the expression more tightly when a short word could appear in unrelated lines.

3. Apply the deletion in place only after the preview shows the intended rows.

   $ sed -i.bak '/status=remove/d' cleanup-list.txt

   The d command removes every line that matches the address. Keep the .bak backup until the edited file has been reviewed.

   The sed -i.bak form creates cleanup-list.txt.bak before saving the edited file, which avoids the GNU/BSD difference around no-backup in-place edits.

4. Confirm the edited file still contains the keep rows and no matching remove rows.

   $ cat cleanup-list.txt
   host=db-01 status=keep
   host=web-01 status=keep
   host=cache-01 status=keep

   The absence of status=remove rows in the final file is the success check. If a needed row disappeared, restore from cleanup-list.txt.bak and narrow the pattern before running sed again.