What is the interpreter in command line?

Using Groups of Commands

Now that you are familiar with different input and output command redirection techniques, let's discuss how you can group commands to create a single command line. When you group two or more commands using symbols such as &, &&, and | |, the command interpreter processes the commands either in a sequence or based on certain conditions, depending on which symbol you used. You can also group sets of commands using parentheses. When you use commands with special symbols, the process is known as a chaining of commands. The following sections explain how to use these symbols.

DSQuery Quota

You use the DSQuery Quota command to search for quota entries for security principals in the Active Directory database according to the specified search criteria. Quota refers to the maximum number of objects that a security principal [user, group, computer, or InetOrgPerson] can own in an Active Directory partition. The syntax of this command is:

This command does not allow you to use the scope parameter for the search. You are also not allowed to use the samid option with the –o parameter. Table 10.5 explains the parameters special to the DSQuery Quota command.

Table 10.5. Parameters of the DSQuery Quota Command

If the search criteria you specify do not return any results or return incorrect results, you can use the DSQuery * command. This command provides a more generalized search of the user accounts stored in the Active Directory database. For a description of common parameters, please refer to the section “Parameters Common to All DSQuery Commands,” earlier in this chapter. You can pipe the output of the DSQuery Quota command as input to other DS commands, such as DSGet, DSMove, DSMod, and DSRm.

NOTE

The command interpreter reads as a string the value specified with the –qlimit Filter parameter used with the DSQuery Quota command. You must always enclose the value of the Filter option in quotation marks. Thus, valid values for the Filter option should read as –qlimit “=100”, –qlimit ”=500”, and so on. Note that even mathematical operators, such as =, =, are to be enclosed in quotation marks. There should be no space between the mathematical operator and the numerical value.

Overview of the NETSH Commands

The NETSH commands run within the NETSH command interpreter. To use NETSH you need to start the NETSH command interpreter from within the command prompt window, as follows:

Type NETSH at the prompt and press Enter. This will change the prompt to the netsh> context prompt. As with most Microsoft command-line utilities, typing a ? at the prompt will provide you with a list of available commands.

Publisher Summary

BASH is a command interpreter that is a way for users to submit instructions to the computer. The general format of a BASH command is command-option[s] parameter[s]. There are a number of commands that helps a user to look for files. The find is very flexible, requiring a place to start, and what to look for, such as find/home-name file 1 looks for a file named “file1” in the /home directory. Anything capable of moving information in or out of Linux system has a device file in the /dev subdirectory. Block special device files move data in and out of hardware connected to the system in large chunks, and use buffers to improve efficiency, such as hard drives, USB, and tape drives. Character device files move data a single character at a time and are unbuffered. Files frequently have an extension to help indicate what they contain, which may not be so obvious, and file can sort through things with a syntax file [filename]. The ls-F command lists files with various file types tagged for easier recognition. While the file and test commands are more useful within scripts, ls-F is more helpful for humans and classifies the file with a special character denoting what it is, such as / for directory, @ for a link file, and * for an executable file.

Regular Backups

It is also important to perform regular data backups. When backups are performed, the data on a computer is copied to other media [such as tape], which can then be stored in another location. If a problem occurs with the source data, you can restore any files that were damaged or lost. For example, if a user accidentally deletes a file or a server’s hard drive crashes, a backup can be restored and all files returned to their previous state.

Windows Server 2003 also provides Automated System Recovery and the Recovery Console for restoring systems that have failed.

Recovery Console is a text-mode command interpreter that can be used without starting Windows Server 2003. It allows you to access the hard disk and use commands to troubleshoot and manage problems that prevent the operating system from starting properly. With this tool, you can do the following:

Enable and disable services.

Format hard disks.

Repair the master boot record and boot sector.

Read and write data on FAT16, FAT32, and NTFS drives.

Perform other tasks necessary to repairing the system.

You can start Recovery Console from the installation CD for Windows Server 2003, or you can install it on an x86-based computer. When installed on the computer, Recovery Console can be run from a multiple-boot menu that appears when the computer is first started. Either method will start the same program and allow you to enter different commands to repair the system.

Automated System Recovery [ASR] allows you to back up and restore the Registry, boot files, and other system state data, as well as other data used by the operating system. An ASR set consists of files that are needed to restore Windows Server 2003 if the system cannot be started. When you create an ASR set, the following items are backed up:

System state data

System services

Disks that hold operating system components

In addition, ASR creates a floppy disk that contains system settings. Because an ASR set focuses on the files needed to restore the system, data files are not included in the backup.

You should create an ASR set each time a major hardware change or a change to the operating system is made on the computer running Windows Server 2003. For example, if you install a new hard disk or network card, or apply a security patch or service pack, you should create an ASR set. Then, if a problem occurs after upgrading the system, you can use the ASR set to restore the system to its previous state [but only after you’ve attempted other methods of system recovery].

ASR should not be used as the first step in recovering an operating system. In fact, Microsoft recommends that it be the last possible option for system recovery and be used only after you’ve attempted other methods. In many cases, you’ll be able to get back into the system using Safe Mode, the Last Known Good Configuration or other options.

To create an ASR set, use the Windows Server 2003 Backup utility. On the Welcome tab of the Backup utility, click the Automated System Recovery Wizard button. This starts the Automated System Recovery Preparation Wizard, which takes you through the steps of backing up the system files needed to recover Windows Server 2003 and creating a floppy disk containing the information needed to restore the system.

Installing and Using the Recovery Console

The Recovery Console is a text-mode command interpreter that can be used without starting Windows Server 2003. It enables you to access the hard disk and use commands to troubleshoot and manage problems that prevent the operating system from starting properly. With this tool, you can do the following:

Enable and disable services

Format hard disks

Repair the master boot record and boot sector

Read and write data on FAT16, FAT32, and NTFS drives

Perform other tasks necessary to repairing the system

The Recovery Console can be started from the installation CD for Windows Server 2003, or you can install it on an x86-based computer. When installed on the computer, you can run it from a multiple-boot menu that appears when the computer is first started. Either method starts the same program and enables you to enter different commands to repair the system.

Configuring & Implementing…

III.C.2. Shell

The second major component of Linux is the shell, which functions as a command interpreter. Although Linux enables users to select the shell of their choice, by far the most widely used shell is the GNU Project's Bourne Again Shell [bash]. The shell runs in text mode; if X is running, it runs in a terminal window.

The bash shell is a fully programmable shell with many advanced features, including aliases, job control, filename completion, command history, shell functions, and much more. Although difficult to learn and use, it provides a powerful environment for executing text-mode programs and scripts.

4.2.4 Shell: Command-Based User Interface

A user can interact with the operating system through a special process, the command interpreter using a command language. A command language can be either very simple in the early days or as powerful as a regular programming language. Most UNIX systems offer one or more command interpreter with a name called shell or its variations. Unfortunately, the term shell may cause some confusion because it is also used by researchers as a generic term to denote the layer of software for users to interact with an operating system. When any user logs in, a shell is started up. The shell has the terminal as standard input and standard output. It starts out by displaying a prompt symbol, such as a dollar sign, indicating that it is waiting to accept a command. For example, if the user types:

who,

the shell creates a child process and runs the who program as the child. The shell is waiting until the child process is terminated. When the child finishes, the shell displays the prompt again and waits for the next command.

UNIX's shell offers a regular programming capability to its users such that its users can request very rich services from the operating system. In addition to the common flow control constructs, shell offers several unique features: I/O redirection, pipelining, and background job execution.

A user can specify standard output to be redirected to a file by typing, for example:

who>outfile.

Similarly, standard input can be redirected from another file, as in:

sortoutfile ,

which invokes the sort program with input taken from file infile and output sent to outfile.

The output of one program can be used as the input for another program by connecting them with a pipe. Thus, the command:

who|wc> dev/tty10

invokes the who program to list all users currently logged in the system and sends the output to wc to count the number of entries. The output of wc is redirected to a file, /dev/tty10 which by convention is a special file denoting a terminal.

If a user put an ampersand after a command, the shell does not wait for it to complete. Instead it just gives a prompt immediately. For instance, the command:

ccfile.c&

starts up a compiling job in the background, allowing the user to continue working as the compiler is running.

Duplicating and Comparing Disks

It's easy to duplicate floppy disks using the Diskcopy command; then you can compare the copied disk to the original disk using the Diskcomp command [covered shortly]. Diskcopy is particularly useful when you want to make copies of a particular disk for distribution. The disks can be made bootable for starting up new computers that do not have any operating systems installed. The commands work even if you have only a single floppy disk drive in your computer. They are explained in the following sections.

Starting the Windows Command Shell

The first step in learning to work with command-line utilities is to determine the different methods you can use to start the Windows command shell. The Windows command shell, in turn, starts the command interpreter.

The Windows command shell is actually an application built into the Windows operating system. CMD.exe is the command interpreter that accepts your commands and executes them in the way you want. You can access the Windows command shell in one of the following ways:

Click Start | Run and type cmd in the Open field of the Run dialog box. Click OK or press Enter.

Click Start | Programs | Accessories and click Command Prompt.

Either of the aforementioned actions will open the Windows command interpreter and provide you with a 32-bit environment for executing commands. You can also place a shortcut for the command prompt on your desktop if you will be using it often. Figure 1.1 shows the command shell.

The command interpreter executable, CMD.exe, is placed in the %SystemRoot%\System 32 folder. In Windows XP, the command shell window title will read C:\Windows\System32\CMD.exe, and in Windows 2003, it will simply read Command Prompt. By default, the command shell starts in the user profile folder of the currently logged on user. That's why the current working directory is shown as C:\Documents and Settings\Administrator in Figure 1.1.

A blinking cursor following the command prompt indicates that it is in interactive mode. This mode allows you to enter commands directly at the prompt and press the Enter key to execute them. For example, if you type the command Dir at the command prompt and press the Enter key, the command will execute immediately and the results will appear in the window. You can also write a series of commands and save them as a batch file. When the batch file is executed, the command interpreter reads the commands, one line at a time, and executes them in order. You can also group multiple commands in a single command line and process them sequentially. We discuss these techniques, along with the basics of batch files, in Chapter 2.