go templates - Concatenate variable in string

Question

How can I concatenate a variable in a string that is used a Go template? This is the original line (from https://github.com/nginx-proxy/nginx-proxy/blob/master/nginx.tmpl):

{{ $host := trim $host }}
{{ $is_regexp := hasPrefix "~" $host }}
{{ $upstream_name := when $is_regexp (sha1 $host) $host }}

{{ $access_log := (or (and (not $.Env.DISABLE_ACCESS_LOGS) "access_log /var/log/nginx/access.log vhost;") "") }}

I am trying to use variable "host" in that string like this:

{{ $host := trim $host }}
{{ $is_regexp := hasPrefix "~" $host }}
{{ $upstream_name := when $is_regexp (sha1 $host) $host }}

{{ $access_log := (or (and (not $.Env.DISABLE_ACCESS_LOGS) "access_log /var/log/nginx/" + $host + "_access.log vhost;") "") }}

But I get this error:

Unable to parse template: template: nginx.tmpl:175: illegal number syntax: "+"

question from:https://stackoverflow.com/questions/65926567/concatenate-variable-in-string

Answer 1

It works making use of printf

{{ $host := trim $host }}
{{ $is_regexp := hasPrefix "~" $host }}
{{ $upstream_name := when $is_regexp (sha1 $host) $host }}
{{ $access_log := (or (and (not $.Env.DISABLE_ACCESS_LOGS) (printf "%s%s%s" "access_log /var/log/nginx/vhosts/" $host "_access.log vhost;")) "") }}