Then in crontab you'd set something like 0 0 * * * doEveryDay. It is one of the most popular toolkits for the Wayland and X11 windowing systems. The callback way to write it is simply: #! /bin/bash GTK (formerly GIMP ToolKit then GTK+)4 is a free and open-source cross-platform widget toolkit for creating graphical user interfaces (GUIs).5 It is licensed under the terms of the GNU Lesser General Public License, allowing both free and proprietary software to use it. The non-callback way to write the script is: #! /bin/bash Say you have a script called doEveryDay.sh. One of the simplest example of callback in bash is one a lot of people are familiar with but don't realise what design pattern they are actually using:Ĭron allows you to specify an executable (a binary or script) that the cron program will call back when some conditions are met (the time specification) But if, as you state, you want to have a wider picture with Bash as just an example, then you should know, that the function code may reside somewhere in the memory, and that code may be accessed by that memory location, which is called its address. Bash offers this way neither for functions, nor variables. This one is passing it by address, not by name. I'll complete this answer with one more method of passing a function to another function, which is not explicitly present in Bash. When was the shellshock (CVE-2014-6271/7169) bug introduced, and what is the patch that fully fixes it?.Rm -rf "$ command' bash do and why is it insecure? Scripttmp=$(mktemp -d) # Create a temporary directory (these will usually be created under /tmp or /var/tmp/) Bash doesn’t have a generic callback construct of this kind, but it does have callbacks, for error-handling and a few other situations for example (one has to first understand command substitution and Bash exit modes to understand that example): #!/bin/bash Typical examples in other programming environments are cases such as “download this resource, and when the download is complete, call this callback”. When you use callbacks, instead of placing the use of a set of instructions “geographically”, you describe when it should be called. create file2 as a copy of a file1Īs can be seen from the example, in imperative programming you follow the execution flow quite easily, always working your way up from any given line of code to determine its execution context, knowing that any instructions you give will be executed as a result of their location in the flow (or their call sites’ locations, if you’re writing functions). In typical imperative programming, you write sequences of instructions and they are executed one after the other, with explicit control flow.
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