Next: Brief - Previous: Case Folding - Up: Comparison

### Suppressing Lines Matching a Regular Expression

To ignore insertions and deletions of lines that match a `grep`-style regular expression, use the `-I regexp` or `--ignore-matching-lines=regexp` option. You should escape regular expressions that contain shell metacharacters to prevent the shell from expanding them. For example, `diff -I '^[[:digit:]]'` ignores all changes to lines beginning with a digit.

However, `-I` only ignores the insertion or deletion of lines that contain the regular expression if every changed line in the hunk--every insertion and every deletion--matches the regular expression. In other words, for each nonignorable change, `diff` prints the complete set of changes in its vicinity, including the ignorable ones.

You can specify more than one regular expression for lines to ignore by using more than one `-I` option. `diff` tries to match each line against each regular expression.