Bash
stristr() in Bash: Case-Insensitive Substring Search
Check whether a string contains a substring regardless of case, with a Bash 4 version, a Bash 3.2 fallback using nocasematch, and a PHP-style stristr().
Topic
substrings
Bash
strstr() in Bash: Check if a String Contains a Substring
Test whether a string contains a substring in pure Bash, or get the rest of the string from the first match the way PHP's strstr() does.
Bash
rm_str() in Bash: Remove a Substring From a String
Delete every occurrence of a substring with one Bash parameter expansion, no sed or tr needed, and the quoting mistakes that make it go wrong.