How to remotely execute shell function

Sometimes it is very convenient to define shell function and execute it remotely.

I will use Bash and assume that it is used by default on a remote server but do not worry as I will show you how to ensure that the proper shell is used.

Define find_setuid function that will be used to find files with setuid permissions. It is quite simple but, at the same time, serves as an excellent example for this use case.

$ function find_setuid() { find $(echo $PATH | tr ":" " ") -user root -perm -4000 -exec ls -lh {} \;; }

I will use declare command to get function definition.

$ declare -f find_suid
find_setuid () 
{ 
    find $(echo $PATH | tr ":" " ") -user root -perm -4000 -exec ls -lh {} \;
}

Execute find_setuid function on remote server assuming that Bash will be used.

$ ssh cloud.sleeplessbeastie.eu "$(declare -f find_setuid); find_setuid"
-rwsr-xr-x 1 root root 31K May 17  2017 /usr/bin/newgrp
-rwsr-xr-x 1 root root 57K May 17  2017 /usr/bin/gpasswd
-rwsr-xr-x 1 root root 133K Jun  5  2017 /usr/bin/sudo
-rwsr-xr-x 1 root root 18K May 24  2017 /usr/bin/pkexec
-rwsr-xr-x 1 root root 45K May 17  2017 /usr/bin/passwd
-rwsr-xr-x 1 root root 40K May 17  2017 /usr/bin/chfn
-rwsr-xr-x 1 root root 31K May 17  2017 /usr/bin/chsh
-rwsr-xr-x 1 root root 35K Mar  7  2018 /bin/mount
-rwsr-xr-x 1 root root 55K Nov 10  2016 /bin/ping
-rwsr-xr-x 1 root root 22K Mar  7  2018 /bin/umount
-rwsr-xr-x 1 root root 31K May 17  2017 /bin/su

Execute find_setuid function on the remote server, ensuring that Bash will be used.

$ ssh cloud.sleeplessbeastie.eu /bin/bash -c "\"$(declare -f find_setuid);find_setuid\""
-rwsr-xr-x 1 root root 31K May 17  2017 /usr/bin/newgrp
-rwsr-xr-x 1 root root 57K May 17  2017 /usr/bin/gpasswd
-rwsr-xr-x 1 root root 133K Jun  5  2017 /usr/bin/sudo
-rwsr-xr-x 1 root root 18K May 24  2017 /usr/bin/pkexec
-rwsr-xr-x 1 root root 45K May 17  2017 /usr/bin/passwd
-rwsr-xr-x 1 root root 40K May 17  2017 /usr/bin/chfn
-rwsr-xr-x 1 root root 31K May 17  2017 /usr/bin/chsh
-rwsr-xr-x 1 root root 35K Mar  7  2018 /bin/mount
-rwsr-xr-x 1 root root 55K Nov 10  2016 /bin/ping
-rwsr-xr-x 1 root root 22K Mar  7  2018 /bin/umount
-rwsr-xr-x 1 root root 31K May 17  2017 /bin/su

Inspect find_setuid function on the remote server, ensuring that Bash will be used.

$ ssh cloud.sleeplessbeastie.eu /bin/bash -vc "\"$(declare -f find_setuid)\""
find_setuid () 
{ 
    find /usr/local/bin /usr/bin /bin /usr/games -user root -perm -4000 -exec ls -lh {} \;
}

Notice, PATH is expanded on the remote server as expected. This is precisely why this shell function serves as an excellent example for this use case.