Anchor(faq46)

I want to check to see whether a word is in a list (or an element is a member of a set).

First of all, let's get the terminoligy straight. Bash has no notion of 'lists' or 'sets' or any such. Bash has strings and arrays. Strings are a 'list' of characters, arrays are a 'list' of strings.

NOTE: A string can not possibly contain a list of other strings because there is no way to reliably tell where each of those other strings end and the next other string starts.

The only proper way to do this is to loop over all elements in your array and check them for the element you are looking for. Say what we are looking for is in bar and our list is in the array foo:

If you need to perform this several times in your script, you might want to extract the logic into a function:

Or, if you want your function to return the index at which the element was found:

If your 'list' is contained in a string, and for some half-witted reason you choose not to heed warning to the note above, you can use the following code to search through 'words' in a string; where a word is defined by any substring that is delimited by whitespace (or more specifically, the characters currently in IFS):

Here's a shorter way of doing it:

And, if for some reason you don't know the syntax of for well enough, here's how to check your script's parameters for an element. For example, '-v':

GNU's grep has a \b feature which allegedly matches the edges of words. Using that, one may attempt to replicate the shorter approach used above, but it is fraught with peril:

Since this "feature" of GNU grep is both non-portable and poorly defined, we recommend not using it. It is simply mentioned here for the sake of completion.