shell function issue - remove the single quote from shell statement
Note: At this point it is not clear what specific shell the OP uses. This answer makes a general point and then discusses bash and zsh.
Your immediate problem is unrelated to quoting: The error message suggests that the executable sshpass is not in your $PATH.
Your string ($cmdstr) doesn't actually contain single quotes - they are an artifact of running bash or zsh with set -x in effect.
However, there are additional issues:
The way you parse the alias definition in cmssh() turns the \\ in your alias definition from a (conceptually) quoted single \ into literal string \\ (two literal \ chars.)
A simple fix in this case is to add another layer of evaluation by having xargs (without arguments) echo the string:
cmdstr=$(alias $aliascmd | cut -d"'" -f2 | xargs)Note that I've eliminated the =-based cut command, which is not needed.
In general, though, parsing alias definitions this way is fragile.
At that point I would expect your code to work in bash, though not yet in zsh (see below).Note that simply removing function from the beginning of your function definition would make your code work in sh (a POSIX-features-only shell), too.
The final problem affects only zsh, not bash:
zsh by default doesn't perform word splitting on $cmdstr in the sshpass -p "$cmpw" $cmdstr command, so that 'ssh mydomain\userxyz@host.com' is passed as a SINGLE argument to sshpass.
To turn on word splitting when evaluating $cmdstr and thus pass its tokens as separate arguments, refer to it as ${=cmdstr}:
sshpass -p "$cmpw" ${=cmdstr}Note that this feature is zsh-specific.