3. UNIX Shell
Enables users to enter commands
Text based
Similar to MSDOS Command
Prompt (but are much more
powerful)
Common Shells
Bourne: sh, ksh, bash
C: csh, tcsh
4. Shell Features
Environment variables and aliases
History of commands used
Programming constructs
Added features in newer shells
Command line editing
Command line completion
Shell configuration files
5. Command History/Editing
Most shells maintain a history of
previously entered commands
history: View list of commands
!#: Rerun command number #
Command line editing
Up/down arrow keys to cycle through list
Left/right arrow keys to move within listed
command
<ctrl><a>: move to start of command line
<ctrl><e>: move to end of command line
6. Command Aliases
Shortcut for command line
Set/view using the alias
command
Examples:
alias ls='ls --color=tty'
alias rm='rm –i'
7. Shell Variables
Customize environment
Shared settings for programs
Assigning Variables: var=“value”
Referencing Variables: $var
Viewing variables: set, printenv
Variables are case sensitive
8. Special Shell Variables
HOME – User’s home directory path
SHELL – Current shell
UID – User’s UID number
PATH – Program search path
PS1/PS2 – Format for command
prompt (prompt for csh/tcsh)
Must use “export” to set variables in shell
9. Parsing the Command Line
Breaks the command line into
components
Special Characters modify
operation
How command runs
Filename Expansion
I/O redirection
Quotes
10. Command Run Modifiers
Write Space – Separate arguments
Newline (<cr>) – End of line
Special Characters
Character Meaning
; Separate multiple command on same line
& Run command in the background
At end of line, continue on next line
|| && Logical operators based on exit status
11. Filename Expansion
Special characters representing
multiple filenames
Also referred to as globbing
Character Matches
* 0 or more characters
? 1 character
[ ] Matches any 1 character in [ ]
(including ranges)
[^ ] Matches any 1 character not in [ ]
(including ranges)
12. I/O Redirection
Modifies how input and output is
used
Chain command to solve bigger
Characters Result
tasks < file Use file as input for command
command
command > file Store command output in file
command >> file Append command output to file
command << label Input from standard input until label
`command` Execute command then replace command
name with its output
cmd1 | cmd2 Use output from cmd1 as input to cmd2
13. Standard File Descriptors
Special file pointers for input and
output
Extension from C language
Name Descriptor Default Device
Standard input (stdin) 0 Keyboard
Standard output (stdout) 1 Screen
Standard error (stderr) 2 Screen
14. Using File Descriptors
Finer control over input/output
redirection
stdout and stderr can be
redirected to same file
Characters Result
command 2> file stderr output stored in file
cmd >& <file-descriptor> Output redirected to <file-descriptor>
Cmd > file 2>&1 Stderr & stdout redirected to file
15. Quote Characters
Prevent special characters from
being interpreted by the shell
Character Name Action
‘ Single Quote Shell ignores all special
characters enclosed ‘ ’
“ Double Quote Shell ignores all special
characters enclosed “ ”
except for $ ‘
Backslash Shell ignores character
immediately following
