format

• https://developer.hashicorp.com/terraform/language/functions/format

format("%s-%s", var.env, var.your-second-string)
PROD-Value-of-your-second-string

See also

• Terraform functions, Terraform collection functions: tolist, toset, length, sum, file, join, depends_on, zipmap, replace, lookup, read files, concat, merge, templatefile, for_each, format, element, slice, try, filebase64, upper, filemd5, coalesce, formatlist, flatten