– EEAA May 26 '11 at 19:11. this is a bit of a script for overwriting random data via a file created that’s 10meg in size to tapes, But, it doesn’t stop when the tape is full,…. : is a shell builtin command. The starting and ending block of while loop are defined by do and done keywords in bash script. Syntax of Bash While … Use the false command to set an infinite loop: #!/bin/bash while false do echo "Do something; hit [CTRL+C] to stop!" Syntax: while[some test/expression] do done Until Loops: Note the first syntax is recommended as : is part of shell itself i.e. As we can see we created a single line while loop but separated while , do and done . done. No, the command in the condition part can be any command (*). s The syntax of the break statement takes the following form: As it is the exit controlled loop, it keeps on executing given lines of codes. Bash While Loop. So, how should this “true” become untrue so it exits please? Now you’re ready to start writing while loops in your bash scripts like a pro! In Bash, break and continue statements allows you to control the loop execution. ; In the end, generally, the increment/decrement of the variable is given. As you are using a regular expression on the right, you indeed need =~ $ while true ; do echo "This is infinite loop. 3. Like while, until tests before each iteration. So, this is how the while loop in Bash works: After the while keyword, the condition is given in the brackets. "; done Bash break Statement # The break statement terminates the current loop and passes program control to the command that follows the terminated loop. Bash While Loop is a loop statement used to execute a block of statements repeatedly based on the boolean result of an expression, for as long as the expression evaluates to TRUE. But, while the conditions are met or while the expression is true. Bash while Single Line Loop. Termination condition is defined at the starting of the loop. For comparison of string, one should use != instead of !=~.. From man bash. A while loop will run until a condition is no longer true. done. while true; do cat big.random.block; | dd of=/dev/st0 bs=1024. Open a text editor to write bash script and test the following while loop examples. When you can write your code in the form. #!/bin/bash while true do echo "Do something; hit [CTRL+C] to stop!" We can create w loop in a single line by using bash ; separator.This will create multiple statements in a single line. Example-1: Iterate the loop for fixed number of times howsoever, the statement after while has to be either TRUE or FALSE. About us: Career Karma is a platform designed to help job seekers find, research, and connect with job training programs to advance their careers. (* or a list of several commands, the last one counts) If the condition evaluates as True, the code after the do keyword executes. It is used to exit from a for, while, until, or select loop. sleep 5; do echo foo; done in bash, dash, busybox sh, ksh93, mksh, lksh, posh, zsh, and yash, all from Ubuntu 16.04's repositories.) Bash scripting has three basic loops, which we will discuss in the following: While Loop: It is the easiest loop that Bash has to offer. So I thought about a while true bash script – user82751 May 26 '11 at 19:07. (until is rarely used, so in case some implementation were nonconforming--though I doubt any Bourne-style shell would treat until in a nonstandard way--I tested until ! 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