conditional pipe in bash

Is there any built-in way in bash to pipe output further if certain test condition is met?

Essentially I want to know if I have to write following function myself or is there some good-practice-already-done way:

check() {
    read temp_var
    test "$temp_var" $@ && echo $temp_var
}

which would be used as follows:

$ echo foo | check == "foo" | cat
=> foo

EDIT: The function above works with all conditions test can comprehend, including numerical ones, such as

$ echo 42 | check -gt 30 | cat
=> 42

String matching, optionally including regex matching

grep is a standard utility which seems to do exactly what you want:

echo foo | grep -x 'foo' | cat

I presume that cat is meant here as a stand-in for a more complex pipeline. If it weren't, then the above, of course, simplifies to:

echo foo | grep -x 'foo'

grep is a powerful utility with many options. See man grep for details.

$ echo 'foo' | grep -x 'foo' | cat
foo
$ echo 'goo' | grep -x 'foo' | cat
$

grep is good for strings. For more complex testing, including comparison, inequality, and numerical tests, awk is very useful. For example:

$ echo 64 | awk '$1 <= 65' | cat
64
$ echo 66 | awk '$1 <= 65' | cat
$

Mathematical expressions can be used:

$ echo 8 | awk '2*$1+1 <= 17' | cat
8
$ echo 9 | awk '2*$1+1 <= 17' | cat
$

Non-numeric ordering can also be tested:

$ echo a | awk '$1 < "b"' | cat
a
$ echo c | awk '$1 < "b"' | cat
$