for i in 'seq 1 10' do echo "$i" done
for i in $(seq 1 10) do echo "$i" done
The intent was to run the code in the single quotes. This would have worked with slanted backticks,
`..`, but here the very similar looking single quotes
'..' were used, resulting in a string literal instead of command output.
This is one of the many problems with backticks, so it's better to use
$(..) to expand commands.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.