Grepping across multiple directories

Question

I want to run this:

grep -r zlib *.cpp

But this fails unless there is a .cpp file in the current directory (in which case only it is searched):

 grep: *.cpp: No such file or directory

Now:

grep -r zlib *

Does search through the whole hierarchy but I want to limit the search to (eg) .cpp files.

Looked through man and a lot of recipe sites but cannot find an answer to what I assume is a simple query - so apologies in advance.

Answer 1

It has nothing do with grep, but with your current shell. The shell expands *.cpp to all the cpp file names in your current directory before running the grep command. Since it can't find any filenames, the glob *.cpp is left unexpanded by the shell. The grep command tries to see this is a file, but cribs that it is not a real file.

You have couple of options, use find

find . -type f -name "*.cpp" -exec grep -r zlib {} +

or if you are using a bash shell, set a nullglob option to stop returning un-expanded glob as a valid result. The (..) is to make the extended shell option temporary and not make it persistent in the shell. The reason to have the --include=*.cpp option is, with the option set, if the glob expansion fails *.cpp becomes empty and your command becomes grep -r zlib which means search in entire sub-directory below.

( shopt -s nullglob; grep -r --include=*.cpp zlib . ; )

Another variant that doesn't include the --include option of grep but using the globstar that allows recursive glob expansion in sub-directories

( shopt -s nullglob globstar; grep -rH zlib **/*.cpp  ; )

Remember the --include= and -H are GNU grep options and not POSIX compatiable

Answer 2

zsh shell users would be quick to point out that they have a built in globbing syntax that allows for this naturally by using a double asterisk:

grep -r zlib **/*.cpp

You can just run 'zsh' as a one time thing if you want by just running 'zsh', you don't have to switch to it permanently.