To disallow input that contains one of many things, you can use a custom data validation rule based the SEARCH function.
In the example shown, the data validation applied to B5:B11 is:
=SUMPRODUCT(--ISNUMBER(SEARCH(...

To extract all matches based on a partial match, you can use use an array formula based on the INDEX and AGGREGATE functions, with support from ISNUMBER and SEARCH. In the example shown, the formula in G5 is:
=IF(F5...

To extract text between parentheses, braces, brackets, etc. you can use a formula based on the MID function, with help from SEARCH function. In the example shown, the formula in C5 is:
=MID(B5,SEARCH("(",B5...

To filter data in case-sensitive way, you can use the FILTER function with help together with the EXACT function. In the example shown, the formula in F5 is:
=FILTER(B5:D15,EXACT(B5:B15,"RED"))
Which...

To test a cell to see if contains certain words but not others, you can use an array formula based on the COUNT and SEARCH functions, wrapped in the AND function.
In the example shown, the formula in C5 is:
{=AND(...

To test if one of several values exists in a range of cells, you can use a formula based on the SUMPRODUCT function. In the example shown, the formula in cell D5 is:
=SUMPRODUCT(--(rng=B5:D5))>0
where "rng" is the...

To sum if cells contain either one text string or another (i.e. contain "cat" or "rat") you can use the SUMPRODUCT function.
Background
When you sum cells with "OR" criteria, you need to be careful not to double count...

To get the position of the first match that does not contain a specific value, you can use an array formula based on the MATCH, SEARCH, and ISNUMBER functions. In the example shown, the formula in E5 is:
{=MATCH(FALSE...

To categorize text using keywords with a "contains" match, you can use the SEARCH function, with help from INDEX and MATCH. In the example shown, the formula in C5 is:
{=INDEX(categories,MATCH(TRUE,ISNUMBER(SEARCH(...

Note: Excel contains many built-in "presets" for highlighting values with conditional formatting, including a preset to highlight cells that contain specific text. However, if you want more flexibility, you can use your...

To check if a cell contains specific text, you can use the SEARCH function together with the ISNUMBER function. In the generic version, substring is the specific text you are looking for, and text represents text in the...

To highlight cells that contain one of many text strings, you can use a formula based on the functions ISNUMBER and SEARCH, together with the SUMPRODUCT function. In the example shown, the conditional formatting applied...

To find the position (row) of the last file revision in a table, you can use a formula based on several Excel functions: MAX, IF, ISERROR, ROW, and INDEX.
In the example shown, the formula in cell H6 is:
{=MAX(IF(...

To count the number of specific words or keywords that appear in a given cell, you can use a formula based on the SEARCH, ISNUMBER, and SUMPRODUCT functions. In the example shown, the formula in C5 is:
=SUMPRODUCT(--...

To test a cell for one of many strings, while excluding others, you can use a formula based on the SEARCH, ISNUMBER, and SUMPRODUCT functions. In the example shown the formula in C5 is:
=(SUMPRODUCT(--ISNUMBER(SEARCH(...