We will be working extensively from the shell (commmand line) in this class. As such it is important that you become both familiar and comfortable working from the command line. Here are some basic concepts:
You access the command line through a terminal program such as Terminal or iTerm on macOS and WSL Ubuntu Linux or Gitbash (installed from GitHub) on Windows.
The shell prompt usually ends with a $ (sh or bash) or % (zsh). After the prompt is where you can type your commands. Here are two prompts, the first from zsh on macOS and the second from bash on Linux:
benson@m2a ~ %
[benson@stargate ~]$
After the prompt you can type a command.
The commands are either built-in to the shell, such as cd, or come from the file system such as ls.
The ls command is used to list the contents of a diretory:
ls with no arguments lists the contents of the current direcory
ls <path> will list the contens of the directory specified by
ls -al will show a detailed listing of files and all files, including those that start with a period “.”. This is useful for seeing file permissions, size, and modification time.
Commands that exist in the file system are found using the PATH environment variable.
When looking for a command in the PATH, it is searched in order from the first directory to the last directory.
You can change what is in the PATH in your .bash_profile (or .zprofile) in your home directory.
For example, you can add the following to .bash_profile or .zprofile, to put ~/.local/bin in your home directory as the first directory in the PATH:
export PATH=~/.local/bin:$PATH
When you open a terminal window, your default directory (the current/present working directory) is your home directory, which is usually something like /Users/benson or /home/benson)
You can show your current directory with the pwd command like this:
$ pwd
/Users/benson
The ~ in a path is expanded to your home directory (e.g., /home/benson).
To change to a directory use the cd command:
cd with no arguments returns you to your home directory
cd <path> takes you to, were can be absolute, like ```cd /home/benson```, or relative, like ```cd project01```
cd .. takes you up one directory level
Use mkdir <name> to create a directory
Use cp <source> <target> to copy a file, where and can be absolute and relative paths.
Use mv <old_name> <new_name> to move (rename) a file from to
To view the contents of a file, you can use:
cat <filename>
To view the contents of a large file, use less, which allows you to “page” through a file with to go forward a page and "b" to go back a page. You can also use the up/down arrows to scroll through a file one line at a time:
less <filename>
The cat command can also be used to creat a file or append to an existing file.
To create a file with cat, you can do the following:
$ cat > foo.txt
FOO
BAR
^D
After you type cat > foo.txt then press ENTER/RETURN, you can type or paste in the contents of the file. To end the file, press CTRL-D (^D), which means to press the CTRL key at the same time as the “D” key.
You can append to an existing file with cat like this:
$ cat foo.txt >> bar.txt
This will add the context of foo.txt to the end of bar.txt
To save on typing on the command line you can create shell aliases
For bash, put aliases in ~/.bash_aliases
For zsh, put aliases in ~/.zshrc
Here are some example aliases
$ cat .bash_aliases
alias lsa='ls -al'
alias m='micro'
alias p3='python3'
alias sg='ssh stargate'
alias ey='ssh euryale'
alias eyvm='ssh euryalevm'
You will need to restart your terminal to have the changes take effect.