cat : concatenate
cat > amit.js
would create new file, ❗❗ BUT, if same file then rewrite.
cat >> amit.js
will give prompt to write something new, and will append to current file.
Note: ❗❗❗
\> : means rewrite
\>> : means append at the end
so, cat amit.js somefile.js > newfile.js
would create new file with contents of amit.js and somefile.js.
grep : find strings within text files
grep "something" filename.txt
would return places where it matches WITHIN FILE
grep "something" -R ./
will return all matching strings with files in current directory.
