"; done Bash while Single Line Loop. The starting and ending block of while loop are defined by do and done keywords in bash script. 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. Like while, until tests before each iteration. Syntax: while[some test/expression] do done Until Loops: string1 != string2 True if the strings are not equal. If the condition evaluates as True, the code after the do keyword executes. 3. When you can write your code in the form. For comparison of string, one should use != instead of !=~.. From man bash. In Bash, break and continue statements allows you to control the loop execution. Bash While Loop. Note the first syntax is recommended as : is part of shell itself i.e. 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. Termination condition is defined at the starting of the loop. It is used to exit from a for, while, until, or select loop. ; In the end, generally, the increment/decrement of the variable is given. 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 (*). Bash break Statement # The break statement terminates the current loop and passes program control to the command that follows the terminated loop. : is a shell builtin command. while (condition) { ... } or . As you are using a regular expression on the right, you indeed need =~ 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. About us: Career Karma is a platform designed to help job seekers find, research, and connect with job training programs to advance their careers. Open a text editor to write bash script and test the following while loop examples. howsoever, the statement after while has to be either TRUE or FALSE. 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,…. #!/bin/bash while true do echo "Do something; hit [CTRL+C] to stop!" So, this is how the while loop in Bash works: After the while keyword, the condition is given in the brackets. – EEAA May 26 '11 at 19:11. Speaking in the long term, that's a much better way to go than implementing a "hack" like you described. Now you’re ready to start writing while loops in your bash scripts like a pro! But, while the conditions are met or while the expression is true. All shell commands have some return value, and the while loop (as well as the if conditional) take return values of zero as "true", and all others as "false". while true; do cat big.random.block; | dd of=/dev/st0 bs=1024. So, how should this “true” become untrue so it exits please? A while loop will run until a condition is no longer true. Use the false command to set an infinite loop: #!/bin/bash while false do echo "Do something; hit [CTRL+C] to stop!" $ while true ; do echo "This is infinite loop. We can create w loop in a single line by using bash ; separator.This will create multiple statements in a single line. 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.) Example-1: Iterate the loop for fixed number of times 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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