These are the most useful commands for myself working on Terminal

cd ..
Change to the parent directory
cd -
Change to the previous directory
open .
Open current folder in Finder
which <command>
Show command path
mkdir <dir1> <dir2> <dirn>
Create directory or directories
rm -r <dir>
Delete all files and then the folder itself
touch <file>
Create a file
rm <file>
Delete the file
cp <original_file> <new_file>
Make a copy file
find . -name <file>
Find the file in current folder
find . -name *<ending>
Find all files with the specified extension
find . -empty
Find all empty files
ln -s <original_path> <symbolic_link>
Creates symbolic link
find . -type f | wc -l
File count under a directory
wc -l filename
Count line number
wc -w < filename
Count word number in a file
grep -o "word" filename | wc -l
Count specific word in a file
head -k filename
Print first k lines
find . -name \*.extension -exec grep -q "specifiedkeyword" '{}' \; -print
Find all specified keyword in all files with an extension
Find all words starting with xy
grep -E '\bxy' filename
grep -E 'xy\b' filename
Find all words ending with xy
head -n +k sourcefile > targetfile
Take and extract first k lines from a file into a target file
cat * > targetfile
Merge all files into one file under a directory
head -n +k sourceFileName > targetFileName
Take first k lines from a file

IMPORTANT: Do not delete python2 folders or files under /System/Library and /usr/bin

Check all Python installations
which python python2 python2.7 python3 python3.6 python3.8
Remove the third-party Python 2.7 framework
sudo rm -rf /Library/Frameworks/Python.framework/Versions/2.7
Remove the Python 2.7 applications directory
sudo rm -rf "/Applications/Python 2.7"
Show symbolic links
ls -l /usr/local/bin | grep '../Library/Frameworks/Python.framework/Versions/2.7'
Remove all symlinks
cd /usr/local/bin/ && ls -l /usr/local/bin | grep '../Library/Frameworks/Python.framework/Versions/2.7' | awk '{print $9}' | tr -d @ | xargs rm
If necessary, edit your shell profile file(s) to remove adding
/Library/Frameworks/Python.framework/Versions/2.7 to your PATH environment file: ~/.bash_login or ~/.bash_profile or ~/.zprofile
If you want to work with python3 instead of Python 2's python, simply add this alias to your ~/.zprofile
alias python='python3'

python3 --version
pip3 --version
Check versions
brew install python3
brew upgrade python3
Install and update Python
python3 -m pip install --upgrade pip setuptools wheel
Update pip, setuptools, and wheel
pip3 install --upgrade <package>
Upgrade packages

katronai/bash-commands.md