Hello, I am a University biology student. I am trying to figure out regular expressions, but I am getting both confused and frustrated trying to group one or more test for use with grep. I was hoping someone here might be able to help.

Given the file: with contents: ""

I would like to use grep to find the value a such that the command is similar to:

However: NONE OF THIS WORKS:
I realize I could just use the comma, but once I need a more complicated expression that would break down.


Thanks!

For efficiency reasons, plain grep only handles the basic set of regular expression operators. Try using egrep or grep -E if you wish to make use of the extended set of operators (I should note that the GNU grep can use the '+' operator, but you have to escape it, eg grep ',\+', just to confuse things)

In general the term 'regular expression' is only loosely defined, and different tools do not always have exactly the same operator set.

1 members found this post helpful.

BTW, is the backslash intended to escape the comma above?

Not only does the comma not have any special regex meaning that needs escaping, but even if it did, only a few characters retain any special meaning when inside a bracket expression. And those are generally handled by careful positioning inside the brackets so that they can't be interpreted as special (the "]" must be the first character in the list, "^" can't be the first, and "-" must be first or last).

Unless your regex is actually meant to match a string of either/both commas and backslashes, in which case it's perfect.

Check out the grep man page and info page for more on how it, and the regexes it supports, operates.

1 members found this post helpful.

Thanks 'neonsignal' and 'David the H.'! That was helpful for getting started.