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The true command is sometimes substituted with the very similar null command, [1] written as a single colon (:). The null command is built into the shell, and may therefore be more efficient if true is an external program (true is usually a shell built in function). We can rewrite the upper example using : instead of true:
The condition/expression is evaluated, and if the condition/expression is true, [1] the code within all of their following in the block is executed. This repeats until the condition/expression becomes false. Because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre ...
The do while construct consists of a process symbol and a condition. First the code within the block is executed. Then the condition is evaluated. If the condition is true the code within the block is executed again. This repeats until the condition becomes false. Do while loops check the condition after the block of code is executed.
While Bash was developed for UNIX and UNIX-like operating systems, such as GNU/Linux, [19] it is also available on Android, macOS, Windows, and numerous other current and historical operating systems. "Although there have been attempts to create specialized shells, the Bourne shell derivatives continue to be the primary shells in use."
for i := 1 : N while A(i) > 0 do etc. That is, a value is assigned to the loop variable i and only if the while expression is true will the loop body be executed. If the result were false the for-loop's execution stops short.
One example of this is Bash, which offers the same grammar and syntax as the Bourne shell, and which also provides a POSIX-compliant mode. [13] As such, most shell scripts written for the Bourne shell can be run in BASH, but the reverse may not be true since BASH has extensions which are not present in the Bourne shell.
From January 2008 to December 2012, if you bought shares in companies when E. William Barnett joined the board, and sold them when he left, you would have a 57.6 percent return on your investment, compared to a -2.8 percent return from the S&P 500.
Bourne-Again shell (bash): written as part of the GNU Project to provide a superset of Bourne Shell functionality. This shell can be found installed and is the default interactive shell for users on most Linux systems. KornShell (ksh): written by David Korn based on the Bourne shell sources [8] while working at Bell Labs; Public domain Korn ...