Bash filesystem

checking for files

[ -e ~/.bashrc ] && echo "path exists"
[ -f ~/.bashrc ] && echo "file exists"
[ -d ~/.vim    ] && echo "dir exists"
[ -L ~/.bashrc ] && echo "symlink exists"

There are many more. See man test.

path components

basename myfile.mp3 .mp3                            #> myfile      # strip file-extension from filename

basename /path/to/myfile.mp3                        #> myfile.mp3  # get filename
dirname  /path/to/myfile.mp3                        #> /path/to   # get dirname
realpath --relative-to=/home /home/will/Downloads  # get relative-path, relative to another (gnu-only)
filename=$(echo $filename | xargs)                   # remove leading/trailing whitespace from variable

[[ "${filepath[1]}" != "/" ]] && filepath="$PWD/$filepath"  # abspath-or-relpath to abspath

writing files

echo 'abc'  > /tmp/test.txt   # write to /tmp/test.txt (replacing contents if exists)
echo 'def' >> /tmp/test.txt   # append to /tmp/test.txt

reading files

by word

for word in $(cat "/path/file.txt") ; do
	echo $word
done

by line

while read line; do
   echo "$line"
done < ~/.bashrc