If you want to search for multiple conditions then you can use OR statements within the regular expression/pattern. There are two approaches, either escape the OR symbol, i.e. \| or use the -E flag.

snippet.bash

# These two are equivalent
grep -E 'a|b' my_file.csv
grep 'a\|b' my_file.csv

If you have multiple conditions or terms you wish to be searched for using grep you can use the -f flag to pass a file of terms to search for.

snippet.bash

# Search for terms in 'file.txt' in files ending in *.py
grep -f file.txt *.py

Here is one solution when you want to chain searches on the output of previous searchesuses recursion which Bash does support and is rarely used, but when it is can be incredibly powerful.

snippet.bash

function chained-grep {
    local pattern="$1"
    if [[ -z "$pattern" ]]; then
        cat
        return
    fi    
 
    shift
    grep -- "$pattern" | chained-grep "$@"
}

• Online grep Regular Expression allows accounts so you can save your regexs.
• Python Regex

• grep, but only certain file extensions