rot13 [options] <file1 ... fileN>
By default, only alphabetic characters are rotated. The -numrot option will also rotate numbers.
If no files are given on the command line, text on standard input will be translated. Output is usually written to standard output, but if the -replace option and a set of files are given, then the files will be translated in place.
This is a very well-known cipher and shouldn't be used for anything that must be kept secret. These days, it is often used for hiding spoilers in public postings. That's about the extent of what it should be trusted for.
A similar such program used to be standard, but it seems to have disappeared.
Copyright 2013 Wayne Morrison
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.