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The detailed semantics of "the" ternary operator as well as its syntax differs significantly from language to language. A top level distinction from one language to another is whether the expressions permit side effects (as in most procedural languages) and whether the language provides short-circuit evaluation semantics, whereby only the selected expression is evaluated (most standard ...
Bash, zsh, and fish have completion for all variable names. PowerShell has completions for environment variable names, shell variable names and — from within user-defined functions — parameter names. Command argument completion is the completion of a specific command's arguments.
The following example shows how command-line completion works in Bash. Other command line shells may perform slightly differently. First we type the first three letters of our command: fir Then we press Tab ↹ and because the only command in our system that starts with "fir" is "firefox", it will be completed to: firefox
The example ~/.bash_profile below is compatible with the Bourne shell and gives semantics similar to csh for the ~/.bashrc and ~/.bash_login. The [ -r filename] && cmd is a short-circuit evaluation that tests if filename exists and is readable, skipping the part after the && if it is not.
If-then-else flow diagram A nested if–then–else flow diagram. In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.
A shell script can be used to provide a sequencing and decision-making linkage around existing programs, and for moderately sized scripts the absence of a compilation step is an advantage. Interpretive running makes it easy to write debugging code into a script and re-run it to detect and fix bugs.
The test command in Unix evaluates the expression parameter. In most recent shell implementations, it is a shell builtin, even though the external version still exists.In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces (this is because [is a program and POSIX compatible shells require a space between the program name and its arguments).
This is an accepted version of this page This is the latest accepted revision, reviewed on 24 January 2025. Family of Unix-like operating systems This article is about the family of operating systems. For the kernel, see Linux kernel. For other uses, see Linux (disambiguation). Operating system Linux Tux the penguin, the mascot of Linux Developer Community contributors, Linus Torvalds Written ...