[Bug 3158] New: ssh-copy-id raises "expr: syntax error" when double-hyphen is passed ("--")

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=3158

            Bug ID: 3158
           Summary: ssh-copy-id raises "expr: syntax error" when
                    double-hyphen is passed ("--")
           Product: Portable OpenSSH
           Version: 8.2p1
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: P5
         Component: ssh-copy-id
          Assignee: unassigned-bugs at mindrot.org
          Reporter: rf at rufflewind.com

Assuming an identity file exists at ~/.ssh/id_rsa.pub, the following
command, which adds a preventative double-dash ("--"):

    ssh-copy-id -i ~/.ssh/id_rsa.pub -- remote-server

will result in the following error:

    expr: syntax error: unexpected argument ‘[-]i’

The error is non-fatal, but it may be confusing to users.

I suspect this is caused by line 110:

    [ "${SEEN_OPT_I}" ] && expr "$1" : "[-]i" >/dev/null && {

Here, "$1" is passed to expr without being validated, so if $1 is "--"
as shown in the command above, this will confuse expr.  I think expr
should be called with "--" to prevent this:

    [ "${SEEN_OPT_I}" ] && expr -- "$1" : "[-]i" >/dev/null && {

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