Beginning Shell Scripting (Programmer to Programmer)


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What Is Shell Scripting?

But it will be present in the directory. And to list the hidden file we need to use —a option of ls. Q 25 By default, a new file and a new directory which is being created will have how many links? Ans: New file contains one link. And a new directory contains two links. The above permissions are mainly assigned to owner, group and to others i.

Here Scripts

The next set of 3 characters indicates the permissions for the other users in the group to which the file owner belongs to. And the last 3 set of characters indicate the permissions for the users who are outside the group. Q 28 What are the different blocks of a file system? Ans: Given below are the main 4 different blocks available on a file system. Super Block : This block mainly tells about a state of the file system like how big it is, maximum how many files can be accommodated etc.

What is bash?

Boot Block : This represents the beginning of a file system. It contains bootstrap loader program, which gets executed when we boot the host machine. So, the information related to these files are stored in an Inode table. Q 31 What are the three modes of operation of vi editor? Q 32 What is the alternative command available to echo and what does it do? Q 33 How to find out the number of arguments passed to the script?

Q 34 What are control instructions and how many types of control instructions are available in a shell? Basically, they determine a flow of control in a program. Q 35 What are Loops and explain three different methods of loops in brief? And it is one of the system variables. By default, its value is space, tab, and a new line. Q 37 What is a Break statement and what is it used for? Ans: The break is a keyword and is used whenever we want to jump out of a loop instantly without waiting to get back to the control command.

When the keyword break is encountered inside any loop in the program, control will get passed automatically to the first statement after a loop. A break is generally associated with an if. Q 38 What is Continue statement and what is it used for? When the keyword continue is encountered inside any loop in the program, control automatically passes to the beginning of a loop.

Continue is generally associated with an if. Q 39 What are Metacharacters in a shell? Explain with some examples.


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They are also called as, regular expressions in a shell. Q 40 How to execute multiple scripts? What we have to do is, we need to mention the name of a script to be called when we want to invoke it. Once after executing script2, the control comes back to script1 which executes a pwd command and then terminates. Q 41 Which command needs to be used to know how long the system has been running?

Ans: uptime command needs to be used to know how long the system has been running. Upon entering the above command at shell prompt i. Q 42 How to find the current shell which you are using? Q 43 How to find all the available shells in your system? Refresh and try again. Open Preview See a Problem? Details if other :. Thanks for telling us about the problem. Return to Book Page. John C. Get A Copy. Paperback , pages. More Details Original Title.

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Some Commonly Used Wildcards

Be the first to ask a question about Beginning Shell Scripting. The output will be Your name is: John Doe. We can save this output in a variable. If you want to write multiple commands on a single line , then use ; as the command separator. We can concatenate two variable by just placing them side by side. As we know everything saved in a variable will be a string, hence we should get We can also use this expression outside the string if we want. But if we need to put single or double quote as a character in a string, we need to escape it with a backslash character. When we reference a string variable and pass it as an argument to a command like echo , Bash breaks the string into different words which were separated by a space and pass them as individual arguments.

This can be useful in certain scenarios like for-in loop. Here is a small example of how Bash does it. I have a small command args that prints the number of arguments passed to it. As you can see from the above result, the number of arguments is three.

Why Should I Learn Shell Programming?

Which means NAME variable was split into three words. But this can also cause problems like if a string contains special characters, it might break our program. So be careful here. If this is not the desired effect we want, we can avoid this by using string interpolation. We just need to wrap a variable in double-quotes. We can perform arithmetic operations in Bash even though Bash does not support number data type.

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We can perform simple arithmetics calculations with let command. Hence, a safe way is to write the expression in quotes which allows adding spaces. Since let would evaluate the expression in a string. Now we know that, based on the operation, Bash will convert string to appropriate data type. We can also declare a variable inside the expression using let or perform an arithmetic operation.

Using this, you can also add spaces in the expression. We can also use expr command to execute an expression which takes multiple arguments it concatenates them and executes it. The above example is very intuitive but simple. At the line no. We can put spaces between the expression which is valid.

Beginning Shell Scripting

This is my favorite syntax for arithmetic expressions as it provides flexibility to print out the result or execute an expression without printing it. We can manipulate variables directly with this syntax. When we write if keyword, it is followed by an expression that evaluates either true or false or a value which is either true or false some languages also supports truthy or falsy values like 0 or 1.

If an expression is used, it is a job of runtime or an interpreter to evaluate the expression and return true or false. In bash, test command is used to evaluate an expression. This command accepts a series of arguments which forms an expression when combined. When an expression is evaluated, it terminates the command with success 0 exit status code or error 1 exit status code.

Based on these values, we can check if an expression is true or false. In the below example, we are checking if the value 5 is greater than 9. We use -gt argument to state a greater than operation. In the above example, all the arguments should be in the order given else test would not understand the operation. In this case, we are not sure if the expression 5 -gt 9 is true or false as nothing was printed to the terminal. Our last command was test 5 -gt 9 and it exited with status 1 which means the expression 5 -gt 9 is false.

Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)
Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)
Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)
Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)
Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)
Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)
Beginning Shell Scripting (Programmer to Programmer) Beginning Shell Scripting (Programmer to Programmer)

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