Hello, World Again

I'd like to try saying "We sometimes take the shell too much for granted," another way.

Advice from masters is often good advice.

Here's my favorite chunk of the greatest of all programming texts, Kernighan and Ritchie's The C Programming Language (Prentice-Hall, 1978).

1.1 Getting Started

The only way to learn a new programming language is by writing programs in it. The first program to write is the same for all languages:

Print the words

hello, world

This is the basic hurdle; to leap over it you have to be able to create the program text somewhere, compile it successfully, load it, run it, and find out where your output went. With these mechanical details mastered, everything else is comparatively easy.

In C, the program to print "hello, world" is

#include

main()

{

printf("hello, world\n");

}

Just how to run this program depends on the system you are using. As a specific example, on the UNIX operating system you must create the program in a file whose name ends in ".c", such as hello.c, then compile it with the command

cc hello.c

If you haven't botched anything, such as omitting a character or misspelling something, the compilation will proceed silently, and make an executable file called a.out. Running that by the command

a.out

will produce

hello, world

as its output. On other systems, the rules will be different; check with a local expert.

Exercise 1-1. Run this program on your system. Experiment with leaving out parts of the program, to see what error messages you get.

Fine advice. Let's do exercise 1-1, but in the shell.

Run the analogous program? Okay.

$ echo hello, world

hello, world

Leave out parts? Let's leave out a part of the string.

$ echo hell, world

hell, world

Or part of the command.

$ eco hello, world

bash: eco: command not found

How about whitespace? It's okay to leave it out of the string,

$ echo hello,world

hello,world

but you need some between a command and its arguments.

$ echohello, world

bash: echohello,: command not found

My point: Programing in the shell is quick and easy. You just type. There's no editing, no special naming, no compiling, no a.out file, no loading and running, no need to consult a local expert.

If you type something incomprehensible, the shell gives you an error message and lets you try again, right away.