Catching a pattern anywhere within a string in R

Question

In My_CODE below, I was wondering if there might be a way to replace endsWith() with another function that captures the pattern anywhere (not just the end of a string)?

I tried tidyselect::contains but it seems it doesn't work in this case.

DATA <- read.table(header=TRUE,text =
"
Row           Variables
1     advanced_baseline
2     beginner_baseline
3 intermediate_baseline
4        advanced_post1
5        beginner_post1
6    intermediate_post1
7        advanced_post2
8        beginner_post2
9    intermediate_post2")

library(tidyverse)

My_CODE <- 
DATA |>
  filter(!endsWith(Variables, "baseline")) |> #!!! CAN WE REPLACE `endWith` with `contain`
  mutate(Variables2 = sub("post\\d+", "baseline", Variables),
         Variables = paste0("(", Variables, " - ", Variables2, ")")) |>
  right_join(filter(DATA, endsWith(Variables, "baseline")), #!!! CAN WE REPLACE `endWith` with `contain`
             by = c("Variables2" = "Variables"), suffix = c("_post", "_pre")) |>
  summarize(Variables, Row = list(c(Row_post, -Row_pre)), .by = Variables) |>
  tibble::deframe()