UNIX filenames may contain any character except the / character and can
be any length (up to a max of around 1024 characters). Upper and Lower
case characters are treated as different characters. While there are no
enforced rules about extensions, many compilers insist on them.
Filter
Any program which reads from standard input, performs some unique permutation
on the input and then writes the results on standard output.
Flat File
A text file. Unlike many other systems, standard UNIX applications use
text files instead of imposing particular formatting conventions on the
document. This results in much easier sharing of information between applications
Newline
UNIX does not put both the Carriage Return and Line Feed characters at
the end of each line of text. Instead, it puts just the Line Feed character.
Because this one character serves both to mark the end of a line and to
advance a terminal to the beginning of the next line, it is referred to
as the Newline character
Passwords
UNIX passwords are 8 characters in length and can include almost any character
that can be typed. Upper and lower case characters are different. The characters
which cannot (or should not) be used include #, @, DEL, and backspace.
Search Path
A list of directories to search for executable programs. For the Bourne
and Korn Shells, this is a list of colon separated directories stored in
the PATH environment variable. For CShell and related Shells, this is a
list of space separated directories stored in the path environment variable.
Special Characters
Characters which cause special and/or unexpected things to happen. There
are two major sets of these chacters. Not all shells support or allow all
of these special characters.
Special Terminal Characters
Control-C to interrupt the currently running job
Control-D to signify the End-of-File
Control-O to throw away all output
Control-Q to restart the output
Control-R to retype the entire line
Control-S to pause the output
Control-U to erase the entire line
Control-V to quote the next character
Control-W to erase words
Control-Z to suspend the current job
Control-\ to abort the currently running job
DEL or Backspace to erase characters
Special Shell Characters
" " -- to quote characters
' ' -- to quote characters
\ -- to escape one character
& -- to background a job
` ` -- to redirect output into command line
< -- to redirect standard input
<< -- to read from a here script
> -- to redirect standard output to a file
>> -- to append standard output to a file
| -- to pipe standard output
$ -- to reference a shell variable
~ -- to reference a home directory
? -- to match one character
[ ] -- to match one of a set of characters
* -- to match any number of characters
space -- to separate command elements
tab -- to separate command elements
newline -- to separate commands
; -- to separate commands
! -- to call back command history
Standard Error
The standard place where error message from programs are sent. By default
it will be the user's terminal. It is separate from the output so that
it is possible to notice errors automatically.
Standard Input
The standard place from which input is received by a program. By default
it will be the user's keyboard.
Standard Output
The standard place where output is directed from a program. By default
it will be the user's terminal.
Whitespace
Any string of spaces and/or tabs is referred to as whitespace. Under certain
circumstances (depending on the shell and/or function being used) the Newline
character may also be counted as whitespace. The name comes simply from
the appearance of these characters on a screen: white.
Wildcard
Any special characters used by a shell to represent a sequence of characters
in a filename. UNIX uses * to represent any string of characters (not containing
a /), ? to represent any one character (except for /) and [..] to represent
any one character from the set between the square brackets (again, / cannot
be matched).