Use regex for file matching, not string matching

Question

I'm trying to figure out how to use grep to search for for a specific string, (for the sake of simplicity) say "9", and I want to search for this, again for simplicity, on all files containing the character b.

I tried grep -e "9" b, but it says it can't find file b. (The same if I don't use the -e option).

I know that I could go for grep -e "9" *b*, but that's not my point. I want the usual tools of regular expressions to use for filename matching.

I'm not interested in convoluted ways of obtaining this. I'm hoping there is a simple option in grep that I can use for this. I perused the man and I can't find anything useful, but I'm pretty new to shell scripting, so I could very easily be missing it.

Is it possible to use regular expression for filename matching using just grep? If so, how?

Answer 1

There is no option in the grep itself to match files using regexp.

You have two options:

1. Use shell glob, like

   grep -e '9' b*
   

   The above is very simple example, but you can match really fancy filenames, especially if you use some of the extension mechanisms. Bellow is a list of some useful bash's feature which can be switched on, similar can be found in zsh and possible other shells:

   • globstar (uses ** to match whole directory tree)
   • nocaseglob (case-insensitive match)
   • extglob (extended patterns: ?(), @(), !(), *(), +())
   • nullglob (non-matching patterns expand to null string)

2. Use find to search for files and on execute grep from it:

   find . -name 'b*' -exec grep '9' {} +
   

   or if regex is needed:

   find . -regex './b.*' -exec grep '9' {} +
   

   The advantage of this method is that you can add another switches to find to select files not only by names but also by dates, sizes, etc. That cannot be done with standard shell's globs unless you are using zsh and its powerful glob qualifiers.