Use grep --exclude/--include syntax to not grep through certain files

Use the shell globbing syntax:

grep pattern -r --include=\*.cpp --include=\*.h rootdir

The syntax for --exclude is identical.

Note that the star is escaped with a backslash to prevent it from being expanded by the shell (quoting it, such as --include="*.cpp", would work just as well). Otherwise, if you had any files in the current working directory that matched the pattern, the command line would expand to something like grep pattern -r --include=foo.cpp --include=bar.cpp rootdir, which would only search files named foo.cpp and bar.cpp, which is quite likely not what you wanted.

Update 2021-03-04

I've edited the original answer to remove the use of brace expansion, which is a feature provided by several shells such as Bash and zsh to simplify patterns like this; but note that brace expansion is not POSIX shell-compliant.

The original example was:

grep pattern -r --include=\*.{cpp,h} rootdir

to search through all .cpp and .h files rooted in the directory rootdir.

If you just want to skip binary files, I suggest you look at the -I (upper case i) option. It ignores binary files. I regularly use the following command:

grep -rI --exclude-dir="\.svn" "pattern" *

It searches recursively, ignores binary files, and doesn't look inside Subversion hidden folders, for whatever pattern I want. I have it aliased as "grepsvn" on my box at work.

Please take a look at ack, which is designed for exactly these situations. Your example of

grep -ircl --exclude=*.{png,jpg} "foo=" *

is done with ack as

ack -icl "foo="

because ack never looks in binary files by default, and -r is on by default. And if you want only CPP and H files, then just do

ack -icl --cpp "foo="