Bash Directories – Difference Between / and // in macOS

A "shell" is any software that provides an interface to an operating system. For instance, explorer.exe is the default shell in Windows (though alternatives exist), and on OS X Finder provides much of the same functionality. On Linux/*nix, the shell could be part of the desktop environment (like Gnome or KDE), or can be a separate software component sitting on top of it (like Unity or Cinnamon).

The above examples are all graphical shells that use a combination of windows, menus, icons and other such elements to provide a graphical user interface (GUI) that can be interacted with using the mouse cursor. However, in the context of software like Bash, or writing scripts, "shell" is usually taken to mean a command-line interpreter, which performs largely the same duties as a graphical shell, except is entirely text-based.

Bash is a specific example of a command-line shell, and is probably one of the most well-known ones, being the default in many Linux distributions as well as OS X. It was designed as a replacement for the Bourne shell (Bash stands for "Bourne again shell"), one of the first Unix shells.

Examples of command-line shells on Windows include cmd.exe (aka Command Prompt) and PowerShell.

The problem actually boils down to the different behavior of login and non-login shells. I had set the variables that control history in my ~/.bahsrc. This file is not read when one starts a login shell, it's only read by interactive, non-login shells (from man bash):

When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable. The --noprofile option may be used when the shell is started to inhibit this behavior.

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When an interactive shell that is not a login shell is started, bash reads and executes commands from ~/.bashrc, if that file exists. This may be inhibited by using the --norc option. The --rcfile file option will force bash to read and execute commands from file instead of ~/.bashrc.

Therefore, each time I logged in, or dropped to a tty, or used ssh, the .history file was getting truncated because I had not set it to the right size in ~/.profile as well. I finally realized this and simply set the variables in ~/.profile where they belong, instead of ~/.bashrc

So, the reason my ~/.history was getting truncated was because I had only set the HISTORY variables in a file read by interactive, non-login shells and therefore every time I ran a different type of shell the variables would be ignored and the file would be cut accordingly.