How the shell knows things.
WHAT AN ENVIRONMENT VARIABLE IS
A value available to programs the shell starts.
WHAT THE IMPORTANT ONES ARE
The search path The home directory The current user The shell The language and character set
WHAT THE PATH DETERMINES
Which directories are searched for commands, in order.
WHY IT EXPLAINS ODD BEHAVIOUR
The wrong version of a program runs because it appears earlier.
HOW TO SEE WHICH WILL RUN
Use which or command with the v option.
WHAT export DOES
Makes a variable available to programs the shell starts.
WHY IT MATTERS
Without it, the variable exists only in the shell itself.
WHERE SETTINGS PERSIST
Shell startup files in the home directory.
WHAT THE DIFFERENCE BETWEEN LOGIN AND NON-LOGIN SHELLS IS
Which files are read.
WHY IT CAUSES CONFUSION
A setting that works interactively is absent in cron or scripts.
WHAT TO DO IN SCRIPTS
Set what you need explicitly, rather than relying on inheritance.
WHAT TO NEVER PUT IN ENVIRONMENT FILES
Secrets committed to version control.
WHAT TO CHECK WHEN A COMMAND BEHAVES DIFFERENTLY IN CRON
The path, and the environment generally.
