To get the ^M character, type CTRL+V and press enter:

:%s/\\r\\n/^M/g

Replace control character ^A with tab character:

sed -e "s/$(echo -e \\001)/\\echo -e '\t'/g" file.txt

See Wikipedia for list of control characters.

Search and replace XXX with YYY in all files:

perl -e "s/XXX/YYY/g;" -pi $(find . -type f)

Troubleshooting

If you get this error:

zsh: argument list too long: perl

Your argument list is clearly too long. Use xargs:

find . \
   -type f \
   -exec perl -i -pe's/XXX/YYY/g' {} +

Search and Replace with Sed

Using sed is more complicated, but this should work on at least Linux:

# Find, backup and replace
find . -name "*.rb" -print | xargs sed -i.bak 's/XXX/YYY/g'
# Delete backup files
find . -name '*.bak' -type f -delete

Reference.