Variables in bash

If you want to understand a programming language, start with its variables. I’m learning Bash, so let’s see how Bash variables work.

Bash variables have names, like foo or i2. They’re made of ASCII letters, digits, and _ (and the first char must not be a digit). (Except, possibly, for some “special” variables, like 1, the first argument.)

To assign to a variable, we write assignment statements like:

a=3           # variable `a` gets the value "3"
b1=           # variable `b1` gets the value ""
  FOO= 45     # variable `FOO` gets the value " 45"
echo = baz    # not an assignment! Instead, calls `echo` with two arguments

Notice that they’re all assigned strings, and that whitespace around the = is significant. All bash variables are strings. Yes, bash can treat these variables as integers sometimes, but in “storage”, they are strings.

Bash variables are dynamically scoped. To illustrate:

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