Class 11 and 12 notes

Use a pathname for the executable file, absolute or relative

What is another way to run a command instead of using a Unix command?

$which ls

How to find a pathname for the executable file such as ls

- or --

What symbols come before an option on the command line?

True

Options using two dashes, --, cannot usually be combined

df -h

Shows the amount of space on the various filesystems. What option produces more readable output

kernel

All operations that need to access any hardware must do through what?

Device driver

How does the kernel know how to talk to new pieces of hardware?

tty device driver

What is the program the collects the characters you type at the command line?

Buffer

space in memory that holds data for later processing

When you hit Enter on a PC or Return on a Mac

When does this program send what you have typed at the command line to the shell

Tokens

Once you type the command, The shell now takes the contents of the buffer and breaks it up into?

Parsing

The act of making a list of all the strings on the command line without the spaces

The list of directories the shell must search to find the file to run a command

What does the PATH shell variable contain?

no, that is the responsibility of the program itself

Does the shell check that a program gets the arguments or options it needs?

./work.sh

If you wanted to run the executable script work.sh in your current directory without using bash, what would you type at the command line

A process

Once the shell knows where to find the program, it can ask the kernel to run it. The kernel does this by creating what?

Running program

A process created by kernel and is given its own chunk of RAM is?

it goes into an inactive state called sleep

What does the shell do after it runs the program the user entered at the command line?

it sends an exit status to the shell

What does a program do JUST BEFORE it stops running?

it means that the program encountered no errors

What does an exit status of 0 mean?

it means that the program encountered no errors

What does an exit status of 0 mean?

The command failed

What does exit status greater than zero indicates?

$ echo $?

what is the command to check exit status

Standard input

By default, data is read from the keyboard.

Standard output

by default, data is displayed on the screen.

Standard error

by default, error messages are displayed on the screen.

>

What symbol redirects standard output

<

What symbol redirects standard input

>>

What symbol appending output to an existing file

/dev/null

A special file that discards all data written to it, effective for troubleshooting.

/dev/pts

Whenever we run an ssh client to talk to a Unix machine, it uses an abstraction called a pseudo-terminal and appear in what directory?

tty

What command will show you your pseudo-terminal