I think you had one too many !s in there (for future reference, it's easier to reproduce if you run your code through reprex, as I have in the example at the bottom). With the code as you had it before, I got the warning
Warning message:
Unquoting language objects with `!!!` is soft-deprecated as of rlang 0.3.0.
Please use `!!` instead.
# Bad:
dplyr::select(data, !!!enquo(x))
# Good:
dplyr::select(data, !!enquo(x)) # Unquote single quosure
dplyr::select(data, !!!enquos(x)) # Splice list of quosures
So, as suggested, I modified the !!! to !!:
suppressPackageStartupMessages(library(tidyverse))
test.df <- data.frame(V1 = rnorm(5), test2 = rnorm(5), somethingelse3 = rnorm(5))
str1 <- 'test'
str2 <- 'something'
test.df %>%
select(V1,
!!glue::glue('post_{str1 }') :=
!!rlang::sym(glue::glue('{str1}2')))
#> V1 post_test
#> 1 1.60161906 0.3478237
#> 2 -0.04423129 -0.4359105
#> 3 0.22677650 0.4410487
#> 4 0.45244758 -0.7553246
#> 5 -2.19567192 -1.4972165
Created on 2019-01-10 by the reprex package (v0.2.1.9000)