\owill be a regular 'o' in this context.
# Want literal backslash echo Yay \o/ # Want other characters bell=\a
echo 'Yay \o/' bell="$(printf '\a')"
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 to use
printf (or in bash,
$'\t'). If the sequence in question is
\r, you instead get a SC1012 that describes this.
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.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.