fix(shell): Prevent 'argument list too long' error

I've set the IFS variable to a newline in base-template.sh.

This will prevent the 'argument list too long' error when hook scripts iterate over the STAGED_FILES environment variable with a large number of files.

I made this change in the central `base-template.sh` script to avoid modifying numerous hook scripts, and to be robust for future hook scripts.

I've also added a new test case (tests/step-101.sh) to verify the fix by committing a large number of files.

Author: google-labs-jules[bot]

tests/step-101.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+# Test:
+#   Test that a large number of staged files does not cause an
+#   "argument list too long" error.
+
+# run the default install
+sh /var/lib/githooks/install.sh --non-interactive || exit 1
+
+mkdir -p /tmp/test101 && cd /tmp/test101 || exit 1
+git init || exit 1
+
+# set up a pre-commit hook
+mkdir -p .githooks/pre-commit
+cp /var/lib/githooks/.githooks/pre-commit/list-staged-files .githooks/pre-commit/
+
+# Create a large number of files
+for i in $(seq 1 2000); do
+    touch "file_$i"
+done
+
+# Stage the files
+git add .
+
+# Commit the files
+# This should not fail with "argument list too long"
+OUTPUT=$(git commit -m "Test commit with a large number of files." 2>&1)
+if echo "$OUTPUT" | grep -q "Argument list too long"; then
+    echo "ERROR: The commit failed with 'Argument list too long'"
+    exit 1
+fi
+
+# Check that the commit was successful
+if ! git log -1 | grep -q "Test commit with a large number of files."; then
+    echo "ERROR: The commit was not successful"
+    exit 1
+fi
+
+exit 0