One trick I like to do is to feed two files into awk; /dev/stdin and some other file I'm interested in. Here's an example: lookup the subject names of a list of serial numbers in an openSSL index.txt

    #!/bin/sh
    
    printf %s\\n "$@" | awk -F'\t' '
        FILE == "/dev/stdin" {
            needle[$0] = 1
            next
        }

        needle[$4] {
            print $NF
        }
    ' /dev/stdin /etc/pki/CA/index.txt

I find myself using this idiom (feeding data from a file to awk and selecting it with data from standard input) again and again. It's a great way to scale shell scripts to take multiple arguments while avoiding opening the same file N times, or doing clunky things with awk's -v flag.