SC1001

This \o will be a regular 'o' in this context.

Problematic code:

# Want literal backslash
echo Yay \o/

# Want linefeed
greeting=Hello\nWorld

# Want other characters
carriagereturn=\r

Correct code:

echo 'Yay \o/'

greeting='Hello
World'

carriagereturn=$(printf '\r')

Rationale:

You have escaped something that has no special meaning when escaped. The backslash will be simply be ignored.

If the backslash was supposed to be literal, single quote or escape it.

If you wanted it to expand to something, rewrite the expression. For linefeeds (\n), put them literally in quotes. For other characters, use POSIX printf or bash/ksh $'...'.

Exceptions

None. ShellCheck (as of 2017-07-03, commit 31bb02d6) will not warn when the first letter of a command is unnecessarily escaped, as this is frequently used to suppress aliases interactively.