Linux System Administration

bash Beginnings

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This is a good way to make complex lines more readable.

The shell ignores lines filled with whitespace (spaces, tabs, empty lines). It also

ignores everything from a comment character (

#) to the end of the line. When bash

reads the second line of this script (

echo hello world), it treats the first word (echo)

as the command to run and the other words (

hello world) as its arguments. The echo

command just copies its arguments to its output. The third line runs another echo

command, but with different arguments.

To see what you’ve put in the file hello, you can print its contents to the screen:

admin@server1:~$ cat hello

#!/bin/bash

echo hello world

echo bonjour monde

Pathnames and Permissions

The hello file can be executed by running the bash command with a hello argument:

admin@server1:~$ bash hello

hello world

bonjour monde

admin@server1:~$

Now let’s try to run hello without its bash chaperon:

admin@server1:~$ hello

bash: hello: command not found

Why can’t bash find it? When you specify a command, Linux searches a list of direc-

tories called the path for a file of that name and runs the first one it finds. In this

case, hello was not in any of these directories. If you tell the system what directory

hello is in, it will run it. The pathname can be absolute (/home/admin/hello) or rela-

tive (./hello means the hello file in the current directory). We’ll describe how to spec-

ify the