echo: Argument is treated as multiple arguments

[DoBi]

I just found out, that there is a different behaviour between the C-coreutils echo and the Rust version.

This command leads to an error, while working with the C version:

echo '"\n'CXXFLAGS=-g -O2'\n"'

It leads to this output:

echo '"\n'CXXFLAGS=-g -O2'\n"'
echo: error: Unrecognized option: 'O'

The expected output is:

echo '"\n'CXXFLAGS=-g -O2'\n"'
"\nCXXFLAGS=-g -O2\n"

It seems like the argument is somehow parsed wrong.

[alstolten]

In #1886 I created a failing test case for this. Unfortunately https://docs.rs/clap/2.33.3/clap/struct.Arg.html#method.allow_hyphen_values does not help.