Working with the Unix OS

Introduction to Unix
It works in the opposite way to "chmod". The mask specifies which permissions should NOT be given when a file
is created.
Examples:
$ umask 000 set no masked bits
$ date> myfile1 creates "myfile1"
$ ls -1 myfile1 show file permissions
-rw-rw-rw- 1 fred student 15 Jun 21:45 myfile1
$ umask 026 set umask bits
$ date> myfile2 creates "myfile2"
$ ls -1 myfile2 show file permissions
-rw-r----- 1 fred student 15 Jun 21:46 myfile2
$ mkdir mydir creates a directory
$ ls -ld mydir
drwxr-x--x 1 fred student 15 Jun 21:46 mydir
I/O Redirection
Standard Input
(stdin)
TTY
command
process
Standard Output
(stdout)
TTY
TTY
(stderr)
Standard Error
where: TTY = terminal display (output) or keyboard (input)
command > output-file
To redirect the output from "ls -l" into the a file:
ls -l > mylsfile
">" redirects stdout to be output to a file. Note that errors still output to terminal.
command ">>" output-file
">>" appends stdout to the end of the output-file
ls -l >> mylsfile
If the output file already exists then ">" will overwrite it, whereas ">>" will append to the end of it. If the
output file does not exist then both ">" and ">>" will create a new file.
command < input-file
The command "wc" counts the number of lines, words and characters which it read from stdin.
wc < mylsfile
...the output to TTY may look like:
17 131 1236
"