A Shell
Programmers:
 Mohammad Hassan Ghaed(83105525)
 Farhaad Pashakhanloo (83112018)
Teacher:
Ali Kardani
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Table of contents:
 The Explorer
 Variables
 Conditional Structures
 Loops
 Batch Files
 Redirecting the Output
 External Commands
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The Explorer
Using the Shell you can browse the computer for files and
directories. You can set the Shell’s Path’s. The Shell enables you
to execute .exe files by typing their names.
Here are some of the commands involving the explorer:
Cd
The cd command changes the current directory. It can be used in
different ways:
Syntax1: cd [directory to change to]
Syntax2: cd ..
The first syntax changes the working directory to a specific one
and the second syntax changes the current directory to the one
which is one level upper than current directory.
Path
The path command can be used in two ways:
Syntax1: path
Syntax2: path [path to append]
The first syntax lists current paths
The second syntax appends the path in the first argument to path
and then lists current paths
Clearpath
The clearpath command can be used to delete all current paths
Syntax :clearpath
Dir
The dir command lists the directories and files in current directory
Syntax: dir
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Variables
You can define your own variables as shell variables. Variables
may be of type int/float/string.
Variables can be set to their initial value at the time of creation or
can be assigned to valid values using assignment syntaxes.
Variables can be used in FOR and IF structures in batch files.
These are the commands involving variables:
Int
The int command is used to define a new variable of type int
Syntax: int [variable name] [optional variable value]
This creates an integer variable named [variable name] with initial
value of [optional initial value]
If no value is specified 0 is assigned to the variable
Float
The float command is used to define a new variable of type float
Syntax: float [variable name] [optional variable value]
This creates a floating point variable named [variable name] with
initial value of [optional initial value]
If no value is specified 0 is assigned to the variable
String
The string command is used to define a new variable of type string
Syntax: string [variable name] ["optional variable value"]
This creates a string variable named [variable name] with initial
value of [optional initial value]
If no value is specified, “” is assigned to the variable
Clearvars
The clearvars command removes all the variables from the
memory
Syntax: clearvars
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Assignments
Syntax1: [variable] = [variable/value]
Syntax2: [variable] = [variable/value] [operand] [variable value]
In the first syntax the right and left side of the equation must be of
the same type. Note that for string values double quotations should
be used.
In the second syntax, in case of integer and floating point values
and variables any assignment is valid. This includes operands +-/*.
But when using strings in the second syntax only the + operand is
valid and it adds the second variable to the end of the first one (cats
it.)
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Conditional Structures
The If commands is used to execute a block of commands if a
condition is satisfied.
Syntax: if [1st variable name/value] [</=/>] [2nd variable
name/value]
{
[Block of commands which may contain internal FOR's and IF's]
}
else
{
[block of commands which may contain internal FOR's and IF's]
}
Note that if command can only be used in batch files.
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Loop structures
The for command is used to execute a block of commands several
times in *.shl batch files
Syntax: for [variable name] [initial value] [final value]
{
[block commands which may contain internal FOR's]
}
If the variable does not exist it is created automatically
Note that for command can only be used in batch files.
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Batch Files
The Shell can run files with the extension .shl as batch files. Each
line of the Batch file is interpreted as user input.
User can pass arguments to batch file. These arguments must be
separated by spaces. At any point in the batch file you can access
these arguments by using %n syntax where n specifies the
argument number starting from 1.
Note that for and if commands can only be used in batch files.
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Redirecting the Output
At any time the output of the Shell can be redirected to a file using
out command.
Syntax: out [std/target file path]
For example the following line redirects the output to the file
c:\new.txt
Out c:\new
The redirection is continued until the Shell reaches this line:
Out std
After that the output will be printed to the monitor.
There is another way of redirecting the output of one line:
Syntax: [commandline to execute] > [target file path]
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External Commands
At present, the Shell has two external commands. These
commands are precompiled exe files that get their arguments from
the shell. Anyone can add his own external commands to the shell
easily.
Help
Syntax1: help
Syntax2: help [command]
The first command guides the user how to use help
The second syntax gives information on any command
Copy
The copy command is an external command like help and is
executed using a compiled exe file and passing the arguments to it
Syntax: copy [source file] [destination directory]
This syntax copies the source file to the destination. If the source
file is in current path there is no need to specify its path
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