tcsh scripting mcsr basic
TRANSCRIPT
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Introduction to Unix Shell&
Scripting with csh/tcshBrief Unix History
Unix Shell & FlavorCSH/TCSH Scripts
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Unix Family Tree
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Unix Architecture
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Unix History and Motivation
The first version of Unix came from AT&T in theearly 1970s (Unix is old!).
Unix was developed by programmers and for programmers .
Unix is designed so that users can extend thefunctionality To build new tools easily and efficiently To customize the shell and user interface.
To string together a series of Unix commands to createnew functionality. To create custom commands that do exactly what we
want.
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What is Shell?
Shell is
Command Interpreter that turns text that youtype (at the command line) in to actions:
User Interface: take the command from user
Programming Shell can do
Customization of a Unix session
Scripting
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Customization of a Session
Each shell supports some customization. User prompt
Where to find mail
Shortcuts (alias)
The customization takes place in startup files
Startup files are read by the shell when itstarts up
The Startup files can differ for different shell
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Types of Shells
Interactive vs. Non-interactive; login or not
Interactive login shell started after login
Non-interactive shell Present when shell script is running
Just inherits parent‟s environment
Interactive non-login shell started Started from a command line
Copies parent environment then invokes~/.bash_rc (or ~/.cshrc or ~/.tcshrc)
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Popular Shells
sh Bourne Shell
ksh Korn Shell
csh,tcsh C Shell (for this course) bash Bourne-Again Shell
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Families of Shells
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Flavors of Unix Shells
Two main flavors of Unix Shells Bourne (or Standard Shell): sh, ksh, bash, zsh
• Fast
• $ for command prompt
C shell : csh, tcsh• better for user customization and scripting
• %, > for command prompt
To check shell: % echo $SHELL (shell is a pre-defined variable)
To switch shell: % exec shellname (e.g., % exec bash)
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Startup files sh,ksh:
/etc/profile (out-of-the-box login shell settings)/etc/profile.local (addtnl. local system settings)~/.profile (addtnl. user customized settings)~/.kcshrc (non-login shell user customization)
bash:/etc/profile (out-of-the-box login shell settings)/etc/bash.bashrc (out-of-box non-login settings)
/etc/bash.bashrc.local (global non-login settings)~/.bash_profile (login shell user customization)
~/.bashrc (non-login shell user customization)
~/.bash_logout (user exits from interactive login shell)
csh/tcsh:
/etc/login (out-of-the-box login shell settings)/etc/csh.login (non-login shell customizations)/etc/csh.login.local (global non-login settings)
~/.login: (login shell user customizations)
~/.cshrc: (non-login shell user customizations)
~/.cshrc.logout: (non-login shells at logout)
~/.logout: (read by login shells at logout)
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Some Special Keys Under tcsh
Ctrl-U = Delete everything on the command-line
Ctrl-A = Move cursor to the front Ctrl-E = Move cursor to the end Ctrl-P = Set the current command-line to the
previous command
Ctrl-N = Set the current command-line to thenext command TAB = Filename completion
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Don‟t forget your Best Friend
% man command (e.g., % man ls)
shows information about the command
usually space or Enter for more information
q to quit
% man man
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Create a shell script
Creating a simple shell script A shell script is a file that contains commands that the shell can
execute.• Any commands you enter in response to a shell prompt.
A utility
A compiled program
Another shell script
• Control flow commands
Run a shell script Enter the script filename on the command line
The shell interprets and execute the commands one afteranother
Why shell script? Simply and quickly initiate a complex series of tasks or a
repetitive procedure.
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Shell programmingMake the file executable
When you create a shell script using a editor,does it have execute permission typically?
• Example: (Make sure you are using tcsh/cshscript!...)
willow> echo $SHELL
/bin/tcsh
willow> ./test
./test: Permission denied.
willow> ls -l test-rw-r--r-- 1 student ums 33 Sep 18 16:33 test
willow> chmod +x test
willow> ./test
This is Test!
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Invoking a Shell script
Give the shell a command on the command line
The shell forks a process
• Which creates a non-interactive duplicate of the shell process
The newly forked process attempts to exec the command
• If the command is an executable program Exec succeeds
System overlays the newly created subshell with theexecutable program
• The command is a shell script
Exec failed The command is assumed to be a shell script
The subshell runs the commands in the shell.
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Invoking a Shell script The shell itself is program
It can be run as a command in a shell andalso accepts arguments. Note: Let‟s find your default shell executing “echo $SHELL”
willow> echo $SHELL
/bin/tcsh
To run a shell script
Which does not have executable permission
Ex: willow>tcsh test Run the script with different shell other than
your interactive shell
Ex: willow>sh test
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Invoking a Shell script
Put special characters on the first line of a shell script To tell OS checks what kind of file it is before attempting to
exec it
To tell which utility to use (sh, csh, tcsh, …)
Special sequence The firsts two character of a script are #! Then followed by the absolute pathname of the program that
should execute the script
Ex:willow> more test
#!/bin/tcsh# This line will not run since it is commented out...
echo 'This is Test!‘
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Make a comment #
Comments make shell scripts easier toread and maintain
Pound sign (#) start a comment line untilthe end of that line as second line inprevious example, except
#! In the first line.
Or inside quotes
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Parameters and Variables
A shell parameter is associated with a value that isaccessible to the user. Shell variables
• Names consist of letters, digits and underscores By convention, environment variables use UPPERCASE
• User created variables (create and assign value)• Keyword shell variables
Have special meaning to the shell Being created and initialized by the startup file
Positional parameters• Allow you to access command line arguments
Special parameters• Such as
The name of last command The status of most recently executed command The number of command-line arguments
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Positional Parameters
The command name and arguments arethe positional parameters.
Because you can reference them by their
position on the command line
$0 : Name of the calling program
$1 - $9 : Command-line Arguments
• The first argument is represented by $1• The second argument is represented by $2
• And so on up to $9
• The rest of arguments have to be shifted to be able
to use $1- $9 parameters.
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Positional Parameters
Example:•Change directory to your assigned numbered subdirectory
willow> cd 1
•List the directory contents, confirming display_5args
willow> ls -l display_5args
•Change mode of display_5args to executable
willow> chmod +x display_5args
•Execute the script
willow> ./display_5args 1 2 3 4 5
you are running script ./display_5args with parameter 1 2 3 4 5
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Positional Parameters
$1-$9 allows you to access 10 arguments How to access others?
Promote command-line arguments: shift Built-in command shift promotes each of the
command-line arguments.• The first argument ( which was $1) is discarded• The second argument ( which was $2) becomes $1• The third becomes the second
• And so on Makes additional arguments available Repeatedly using shift is a convenient way to
loop over all the command-line arguments
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Positional Parameters
Example:willow> more demo_shift
#!/bin/tcsh
echo $1 $2 $3shift
echo $1 $2
shift
echo $1
willow> ./demo_shift 1 2 3
1 2 3
2 3
3
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willow> more demo_shift
#!/bin/tcsh
echo $1 $2 $3
shift
echo $1 $2
shift
echo $1
shift
echo $?
shift
echo $?
shift
echo $?
willow> ./demo_shift 1 2 3 4
1 2 32 3
3
0
0
shift: No more words.
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Special Parameters
Useful values
Command-line arguments
Execution of shell commands
Can not change the value directly, like positional parameters
Value of Command-line arguments: $* and $@ $* and $@represent all the command_line arguments ( not just
the first nine)
“$*” : treats the entire list of arguments as a single argument
“$@” : produce a list of separate arguments (Only bash/ksh/sh)
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TCSH SCRIPT WITH $*and $@
willow> more for_test#!/bin/tcsh
echo 'using $*'foreach arg ($*)
echo "$arg"end
echo 'using $@'foreach arg ($@)
echo "$arg"end
willow> ./for_test 1 2 3
using $*123using $@Illegal variable name.
BASH SCRIPT WITH $*and $@
willow> more for_test.bash#!/bin/bash
echo "using \$* "for arg in "$*"do
echo "$arg"done
echo "using \$@ "for arg in "$@"do
echo "$arg"donewillow> ./for_test.bash 1 2 3
using $*1 2 3using $@123
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Special Parameters
The number of arguments: $#
Return a decimal number
Use the test to perform logical test on this
numberwillow> more num_args
echo this script is called with $#arguments.
willow> chmod +x num_args
willow> ./num_args
this script is called with 0 arguments.
willow> ./num_args 1
this script is called with 1 arguments.
willow> ./num_args 2
this script is called with 1 arguments.
willow> ./num_args 0
this script is called with 1 arguments.
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Special Parameters
Exit status: $? When a process stops executing for any reason,
it returns an exit status to its parent process. By convention,
• Nonzero represents a false value that the commandfailed.
• A zero value is true and means that the command wassuccessful
You can specify the exit status that a shell script
returns by using the exit built-in followed by anumber• Otherwise, the exit status of the script is the exit status
of the last command the script ran.
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willow> ls a
a: No such file or directory
willow> echo $?
2
willow> echo olemissolemiss
willow> echo $?
0
willow> more exit_statusecho this program will have the exit code of 8.
exit 8
willow> ./exit_status
this program will have the exit code of 8.
willow> echo $?8
willow> echo $?
0
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Summary
A shell is both a command interpreter and a programminglanguage. Job control
Control-z/fg/bg/&
Variables Local and environment variables Declare and initialize a variable ( no type) Export unset
Command line expansion Parameter expansion/variable
expansion/command/substitution/pathname expansion
Quote ( „ „ “ “ \ )• “ “ all but parameter, variable expansion and \ • „ „ suppress all types of expansion • \ escaping the following special character
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Basic Script Examplewillow> more basic_script
#!/bin/tcsh
echo 'Listing the files in long format appending due date/time'
echols -lrtah
echo
echo 'Listing the files in long format appending due date/time'
echo
df -k
# Using diff to find two files differences and writing them to another file
diff -c for_test.bash for_test >> file_differences &
echo
echo 'sleeping mode for 4 seconds. Please wait!'
echo
sleep 4
echo
echo 'GO REBELS'
echo 'To find out the differences of files for_test and for_test.bash, '
echo 'Please open file_differences via using cat command as shown below:'
echo 'cat file_differences‟
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Killing BAD Processes
The “kill” command: kill [-<signal>] <pid>
Send <signal> to process <pid>
The “killall” command: killall [-<signal>] <command>
Send <signal> to all processes that start with<command>
Useful signals (kill –l for the complete list):TERM the default, “term inate”, kills things
nicelyKILL will kill anything, but not nicelyHUP “h angup ”, used to reload
configurationsSTOP stops (suspends) a running process
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Summary
Shell parameters HOME
PATH
PS1
SHELL $0
$n
$*
$@
$# $$
$!
$?