How can I exclude directories from grep -R?

This syntax

--exclude-dir={dir1,dir2}

is expanded by the shell (e.g. Bash), not by grep, into this:

--exclude-dir=dir1 --exclude-dir=dir2

Quoting will prevent the shell from expanding it, so this won't work:

--exclude-dir='{dir1,dir2}'    <-- this won't work

The patterns used with --exclude-dir are the same kind of patterns described in the man page for the --exclude option:

--exclude=GLOB
    Skip files whose base name matches GLOB (using wildcard matching).
    A file-name glob can use *, ?, and [...]  as wildcards, and \ to
    quote a wildcard or backslash character literally.

The shell will generally try to expand such a pattern itself, so to avoid this, you should quote it:

--exclude-dir='dir?'

You can use the curly braces and quoted exclude patterns together like this:

--exclude-dir={'dir?','dir??'}

If you are grepping for code in a git repository and node_modules is in your .gitignore, you can use git grep. git grep searches the tracked files in the working tree, ignoring everything from .gitignore

git grep "STUFF"

Many correct answers have been given here, but I'm adding this one to emphasize one point which caused some rushed attempts to fail before: exclude-dir takes a pattern, not a path to a directory.

Say your search is:

grep -r myobject

And you notice that your output is cluttered with results from the src/other/objects-folder. This command will not give you the intended result:

grep -r myobject --exclude-dir=src/other/objects-folder

And you may wonder why exclude-dir isn't working! To actually exclude results from the objects-folder, simply do this:

grep -r myobject --exclude-dir=objects-folder

In other words, just use the folder name, not the path. Obvious once you know it.

From the man page:

--exclude-dir=GLOB
Skip any command-line directory with a name suffix that matches the pattern GLOB. When searching recursively, skip any subdirectory whose base name matches GLOB. Ignore any redundant trailing slashes in GLOB.

Step 1:

vim ~/.bash_profile

search() {
    grep -InH -r --exclude-dir=*build*  -e "$1" .
}

Step 2:

source ~/.bash_profile

Usage:

search "<string_to_be_searched>"