erl: the interactive shell

Start erl

Run erl with no arguments to start a local shell. The prompt counts up from one, and every answer comes back as a value you can use in the next line.

erl

Eshell V15.2 (abort with ^G)

1>

Type an expression and end it with a period. The shell prints the value and its type hint, then waits for the next one.

Evaluate expressions

Every expression ends with a period. The shell prints the value and its type hint, then waits for the next one.

Strings print as lists of character codes unless you ask for a readable form, which lesson 40 covers.

1> 1 + 2.

3

2> hello.

hello

3> [hello, world].

[hello,world]

4> help().

2> h().

3> q().

1> 1 + 2.

3

2> hello.

hello

3> [hello, world].

[hello,world]

Shell helpers

The help function lists the shell commands. The h function shows the history, and q halts the node cleanly.

1> help().

2> h().

3> q().

1> 2 + 2.

4

2> % * 10.

40

3> v(1).

4

Recall results

The percent sign recalls the previous result, and percent with a number recalls that numbered result. Both work in any later expression.

The v function returns a stored value instead of printing it, which is handy inside a longer line.

1> 2 + 2.

4

2> % * 10.

40

3> v(1).

4

Next: Your first Erlang script

Article author: Arthur Isaev