In the UTF-8 files I audit, the only invisible characters I expect to see… er… not see… are whitespace, horizontal tab and linefeed. All others I call “gremlins”. They include carriage return, no-break space, soft hyphen and another 62 control characters. Gremlins are a nuisance. One gremlin causes a shell to hang. Less evil gremlins lurk inside apparently OK strings and cause the strings to be processed weirdly. This post explains a new script that locates and visualises gremlins in tab-separated tables.

Source: LXer – Hunting gremlins