shell_handout.pdf

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Overview

By the end of this lecture you should...

What are shell scripts?

Creating and running shell scripts.

Shell Programming 1

Know what a shell program is

Using Variables.

Be able to run a shell program

The .profile ﬁle.

Be able to write simple shell programs

Input and Output.

You can download all the sample programs from in this lecture from the course home

page.

Louise Dennis

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Dept. Computer Science and IT

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What is a Shell Script

UNIX Command Line

The shell is a command interpreter – it read commands and then executes them.

Why use Shell?

In UNIX you type commands at the keyboard and the system responds.

It can work interactively or from a text ﬁle.

Every operating system has some sort of command interface.

A shell program is simply a text ﬁle which contains commands you would normally

type at the prompt.

It is always there!!

In UNIX this is a separate program. Shells are different versions of this program.

Anything you can type in a shell script you can type at the command line.

Originally there were two shells, sh and csh .

Major differences between shell scripts and other ﬁles:

– First line is usually

#!/usr/bin/sh

– NB. # is also used for comments.

– It is normally executable.

Lots of legacy code is written in Shell.

sh (by Bourne) was best for programming – writing shell scripts which executed a

sequence of commands.

Its concepts underpin many other scripting languages

csh (by Joy) was best for interactive work

Lots of UNIX applications make more sense if you know a bit of Shell.

bash (Bourne again shell) incorporates combines aspects of both and is a successor

of sh .

MOST IMPORTANT: A shell script is some “glue” with which you stick together

other program.

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The Simple Shell Script in Action

Using a Shell Script

A Simple Shell Script

[lad@bartok examples]$ ls

done.sh

[lad@bartok examples]$ chmod u+x done.sh

[lad@bartok examples]$ done.sh

done.sh

done

[lad@bartok examples]$ sh done.sh

done.sh

done

[lad@bartok examples]$

Create the text ﬁle.

#!/usr/bin/sh

Make it executable (optional): chmod u+x filename

ls

echo "done"

Each command appears on a separate line.

Run it

– sh filename

– filename – only works if ﬁle is executable and your PATH is set correctly.

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Quick Quiz

Variables and Assignment

Some Fundamentals of Programming (Revision)

Shell commands are the same as UNIX commands so:

1. Write a shell script to print a ﬁle called shell1.pdf

2. Write a shell script to change the name of a ﬁle called shell1.pdf to a ﬁle called

simple shell.pdf

3. Write a shell script to list the ﬁles a directory and redirect the output to a ﬁle

ls.txt

4. Write a shell script to make the ﬁle, done.sh executable.

Answers handed to me at the end of the lecture with your name and CS login on them

will be eligable for the course prize.

Answers to the quiz will go up on the website after the lecture.

Assigned by = – there must be NO SPACES round the = symbol.

TMP FILE=/tmp/junk

Assignment – giving a variable a value

Input and Output.

Called by $VarName

lpr $TMP FILE

Conditionals – if-then-else and case

Loops – for, while and do

For small programs things like objects classes and methods get in the way. Shell should

only be used for small programs.

To set the variable so its available to other shell scripts and at the command line –

i.e. make it an Environment Variable use export :

export TMP FILE

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Some Details

Your .profile is a shell script

Input and Output

If you want to use whitespace then use "

MESSAGE="Program ends OK"

# set up personal bin directorys

PATH=$HOME/bin:$PATH:

EDITOR=emacs

LASER=het

export PATH TERM EDITOR LASER

DEFTERM=vt100

ASKTERM=false

The ﬁrst argument to a shell script is called $1 .

If you actually need a $ sign use n $

echo "A meal in USA costs n $"

The second argument to a shell script is called $2 .

... and so on.

Similarly you can us n instead of quotes

MESSAGE=Program n ends n OK

Shell uses echo like Java’s println

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Dept. Computer Science and IT

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More Simple Shell Programs

Special Input Variables

Input and Output: An Example

#!/usr/bin/sh

$# Records the number of arguments passed to the shell, not counting the ﬁrst

command.

– simple.sh a b c sets $# to 3.

– One of its primary uses is to check that enough arguments have been speciﬁed

#!/usr/bin/sh

echo $#

echo $1

[lad@bartok examples]$ count_input.sh

0

[lad@bartok examples]$ sh count_input.sh hello goodbye hello

3

[lad@bartok examples]$ sh count_input.sh hello goodbye hello pink

4

$* All the arguments given to the shell

– Useful in loops when you want to do something to every input.

[lad@bartok bin]$ simple.sh hello

hello

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Examples of semi-colons and backlashes

Sequences at Work

Sequences of Commands

#!/usr/bin/sh

#!/usr/bin/sh

Commands are generally terminated by end-of-line.

echo $1

echo $2; echo \

$3

emacs $1

chmod u+x $1

Several commands can be on one line, separated by semi-colons.

To spread a command over more than one line, end the ﬁrst line with an escape n .

[lad@bartok examples]$ edit_shell.sh new.sh

[lad@bartok examples]$ ls -lt

total 52

-rwxr--r--

Leading white space (e.g. tabs) is ignored.

[lad@bartok examples]$ sh echo_three.sh red green blue

red

green

blue

Arguments to commands are separated by white space.

1 lad

staff

8 Nov 26 16:10 new.sh

[lad@bartok examples]$

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Dept. Computer Science and IT

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Examples

#!/usr/bin/sh

Summary

Quotes

FILE=hello1.java

echo ’ls *.sh $FILE’

echo "ls *.sh $FILE"

echo ls *.sh $FILE

echo ‘ls *.sh $FILE‘

Variables: $NAME

Single Quotes Treat as a string.

Double Quotes evaluate variables

No Quotes evaluate variables and wild cards

Back Quotes treat as a command

Assignment: =

Input Arguments: $1 , $# , $* .

Output: echo .

[lad@bartok lad]$ quotes.sh

[lad@bartok examples]$ quotes.sh

ls *.sh $FILE

ls *.sh hello1.java

ls edit_shell.sh list_shell.sh make_executable.sh quotes.sh hello1.java

edit_shell.sh hello1.java list_shell.sh make_executable.sh quotes.sh

Sequences of commands.

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Plik z chomika:

Inne pliki z tego folderu:

So15 - Programowanie wspolbiezne.pdf (52 KB)
So10 - Rozproszona pamiec dzielona 1.pdf (111 KB)
abs-guide.pdf (895 KB)
BASH - Programowanie w powloce.pdf (343 KB)
LinuxPG.pdf (481 KB)

Inne foldery tego chomika:

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