example demo service

# /etc/systemd/system/hello@.service
[Unit]
Description=say hello
OnFailure=hello2.service

[Service]
Type=oneshot
ExecStart=/bin/echo "%I"
ExecStart=/bin/echo "%i"

instance unit with non-path

zeal@epona /etc/systemd/system $ sudo systemctl start "hello@foo-bar.service"
zeal@epona /etc/systemd/system $ sudo systemctl status "hello@foo-bar.service"
● hello@foo-bar.service - say hello
   Loaded: loaded (/etc/systemd/system/hello@.service; static; vendor preset: disabled)
   Active: inactive (dead)

Feb 27 15:11:52 epona systemd[1]: Starting say hello...
Feb 27 15:11:52 epona echo[22733]: foo/bar
Feb 27 15:11:52 epona echo[22734]: foo-bar
Feb 27 15:11:52 epona systemd[1]: Started say hello.

instance unit with simple path name

zeal@epona /etc/systemd/system $ sudo systemctl start 'hello@/foo-bar/baz.service'
zeal@epona /etc/systemd/system $ sudo systemctl status 'hello@/foo-bar/baz.service'
● hello@-foo-bar-baz.service - say hello
   Loaded: loaded (/etc/systemd/system/hello@.service; static; vendor preset: disabled)
   Active: inactive (dead)

Feb 27 15:04:58 epona systemd[1]: Starting say hello...
Feb 27 15:04:58 epona echo[22138]: /foo/bar/baz
Feb 27 15:04:58 epona echo[22139]: -foo-bar-baz
Feb 27 15:04:58 epona systemd[1]: Started say hello.

instance unit with systemd-escape

zeal@epona /etc/systemd/system $ sudo systemctl start "hello@$(systemd-escape /foo-bar/baz).service"
zeal@epona /etc/systemd/system $ sudo systemctl status "hello@$(systemd-escape /foo-bar/baz).service"
● hello@-foo\x2dbar-baz.service - say hello
   Loaded: loaded (/etc/systemd/system/hello@.service; static; vendor preset: disabled)
   Active: inactive (dead)

Feb 27 15:06:54 epona systemd[1]: Starting say hello...
Feb 27 15:06:54 epona echo[22344]: /foo-bar/baz
Feb 27 15:06:54 epona echo[22345]: -foo\x2dbar-baz
Feb 27 15:06:54 epona systemd[1]: Started say hello.