grep: dir: Is a directory

grep: src: Is a directory means one of the arguments you passed to grep is a directory, and without -r GNU grep reads only files. Use grep -r PATTERN src to search every file under it. grep still searches the other arguments, but it exits with status 2 because an error occurred, even when other files matched, so scripts treat the run as failed.

Reproduce the error

mkdir src
echo "TODO: fix" > src/app.js
grep TODO src

grep: src: Is a directory

With a glob, the directory is reported and the files are still searched:

mkdir -p project/src && cd project
echo "TODO: write docs" > notes.txt
grep TODO *

notes.txt:TODO: write docs
grep: src: Is a directory

The match in notes.txt is printed, but the exit status is 2. GNU grep returns 2 whenever an error occurred, unless -q is used and a line was selected. -s (--no-messages) hides the message but keeps status 2.

Fix: search recursively

mkdir src
echo "TODO: fix" > src/app.js
grep -r TODO src
grep -rn --include='*.js' TODO .

src/app.js:TODO: fix
./src/app.js:1:TODO: fix

-r follows symlinks only for the paths on the command line; -R follows all of them.

Fix: skip directories

-d ACTION (--directories=ACTION) controls what grep does with a directory argument: read (the default, which produces this message), skip, or recurse (same as -r):

mkdir -p project/src && cd project
echo "TODO: write docs" > notes.txt
grep -d skip TODO *
echo "exit status: $?"

notes.txt:TODO: write docs
exit status: 0