Get number from line bash
SEE VIDEO BY TOPIC: 16 - Unix - Linux Shell - Search Pattern - Text - String from file - grep CommandContent:
Regular Expressions for Numbers in BASH
Previous Contents Next. Up to now, our scripts have not been interactive. That is, they did not require any input from the user. In this lesson, we will see how your scripts can ask questions, and get and use responses.
To get input from the keyboard, you use the read command. The read command takes input from the keyboard and assigns it to a variable. Here is an example:. As you can see, we displayed a prompt on line 3. Note that " -n " given to the echo command causes it to keep the cursor on the same line; i. Next, we invoke the read command with " text " as its argument. What this does is wait for the user to type something followed by a carriage return the Enter key and then assign whatever was typed to the variable text.
If you don't give the read command the name of a variable to assign its input, it will use the environment variable REPLY. The read command also takes some command line options. The two most interesting ones are -t and -s. The -t option followed by a number of seconds provides an automatic timeout for the read command. This means that the read command will give up after the specified number of seconds if no response has been received from the user.
This option could be used in the case of a script that must continue perhaps resorting to a default response even if the user does not answer the prompts. Here is the -t option in action:. The -s option causes the user's typing not to be displayed.
This is useful when you are asking the user to type in a password or other confidential information. Since we are working on a computer, it is natural to expect that it can perform some simple arithmetic. The shell provides features for integer arithmetic. What's an integer? That means whole numbers like 1, 2, , It does not mean fractional numbers like 0. If you must deal with fractional numbers, there is a separate program called bc which provides an arbitrary precision calculator language.
It can be used in shell scripts, but is beyond the scope of this tutorial. As you can see, when you surround an arithmetic expression with the double parentheses, the shell will perform arithmetic expansion.
The shell can perform a variety of common and not so common arithmetic operations. Try this program out and watch how it handles division remember, this is integer division and how it handles large numbers.
Numbers that get too large overflow like the odometer in a car when you exceed the number of miles it was designed to count. It starts over but first it goes through all the negative numbers because of how integers are represented in memory. Division by zero which is mathematically invalid does cause an error. I'm sure that you recognize the first four operations as addition, subtraction, multiplication and division, but that the fifth one may be unfamiliar.
This operation performs division but instead of returning a quotient like division, it returns the remainder. While this might not seem very useful, it does, in fact, provide great utility when writing programs. For example, when a remainder operation returns zero, it indicates that the first number is an exact multiple of the second. This can be very handy:. Previous Contents Top Next. Shotts, Jr.
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Here is an example:! Here is the -t option in action:! Arithmetic Since we are working on a computer, it is natural to expect that it can perform some simple arithmetic. Let's say you want to use the command line as a primitive calculator. This can be very handy:!
Previous Contents Next. Up to now, our scripts have not been interactive. That is, they did not require any input from the user. In this lesson, we will see how your scripts can ask questions, and get and use responses. To get input from the keyboard, you use the read command.
Keyboard Input and Arithmetic
Shell scripting (bash)
This is a short post on how to recognize numbers such as simple integers, real numbers and special codes such as zip codes and credit card numbers and also extract these number from unstructured text in the popular bash Bourne Again Shell shell or scripting language. Bash is the default Unix console or terminal window on Macintosh computers as well as a number of other Apple products. It is also used by cygwin and several other variants of Unix and Linux. Regular expressions are a compact efficient way of representing patterns of characters including the letters in the English alphabet and digits.
I am glad that you are here! I was working on bioinformatics a few years ago and was amazed by those single-word bash commands which are much faster than my dull scripts, time saved through learning command-line shortcuts and scripting. Recent years I am working on cloud computing and I keep recording those useful commands here. Not all of them is oneliner, but i put effort on making them brief and swift.
Number lines in a file
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Thanks for the question. Another way to do it is with head and tail. Your way might be easier. I want just to edit first line of file by appending something to the first line and rest is same. How should I achieve it??
Bash: String Length – How To Find Out
If you often create Bash scripts, you may sometimes need to get the length of a string or find out the length of a variable that stores some string. This short note shows how to find out the length of a string from the Linux command line and how to count the length of the each line in a file. You will also see how to get the length of a string if it is stored in a variable in Bash and then assign that calculated number of characters to another variable. Cool Tip: Needs to pass arguments to a Bash script? Make it to print usage and exit if they are not provided! Follow the best practice! Cool Tip: Make your Bash script interactive!
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Shell Programming and Scripting