Shell Programming and Scripting

So when would you glob and when would you use regular expressions? I'm still somewhat confused.

Most of the time you won't have the option to choose between using glob or regular expressions, and will have to use what the tool offers. As a general rule of thumb you will be using glob for the shell prompt, and regex for everything else.

For example if from a shell prompt you type ls p* you would expect the shell to expand p* to any file begining with p (glob) not any file with zero or more p's anywhere in the name (regex). Which highlights another difference in glob (patterns span the whole string, like having an implied "^" at the front and "$" at the end with regex).

Here is a little table with glob and regex equivalent

I think I get it -- glob is used for finding filenames and regex is used for matching strings (as in a piece of text)?

More information.
Most things can be found on the command line with 'man'. Try 'man bash' and then search for Pattern Matching with '/Pattern Matching'. Also try 'man grep' and read through the section about REGULAR EXPRESSIONS.

I did a search of the output from 'man bash' with '/regex' and it mentioned the regular expression matching operator '=~', also used in PERL. It says 'matched accordingly (as in regex(3))'. This means I can look up the information with 'man 3 regex' assuming I have the man pages installed from Linux Documentation Project.

Glob patterns can (and usually do) match against filenames. But glob patterns in case options and shell if expressions are tested against strings not filenames eg:

Code:

$ [[ "salad" == s* ]] && echo yes
yes
$ [[ "salad" == s.* ]] && echo yes
$ [[ "s.jpg" == s.* ]] && echo yes
yes

Many languages allow you to use both glob and regex to match strings. PERL, TCL, and Java are a few examples.