How to use Perl one-liners to find and replace across files

Combine -i for in-place editing with glob patterns to process multiple files:

# Replace in all .txt files (with backup)
perl -i.bak -pe 's/old_pattern/new_text/g' *.txt

# Recursively replace in all .pl files
find . -name '*.pl' -exec perl -i.bak -pe 's/foo/bar/g' {} \;

# Or using File::Find in one-liner
perl -MFile::Find -i.bak -e 'find(sub { return unless /\.txt$/; \
  local @ARGV = $_; while(<>) { s/old/new/g; print } }, ".")'

# Case-insensitive replace with regex
perl -i.bak -pe 's/error/warning/gi' *.log

# Only replace if line contains another pattern
perl -i.bak -pe 's/foo/bar/g if /baz/' file.txt

# Preview changes without modifying (remove -i)
perl -pe 's/old/new/g' file.txt | diff file.txt -

Always test without -i first, or use -i.bak to create backups. The backup extension can be any string.