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Command-line argument parsing is the process of analyzing and handling command-line input provided to a program.
The input to eval is not necessarily a string; it may be structured representation of code, such as an abstract syntax tree (like Lisp forms), or of special type such as code (as in Python). The analog for a statement is exec, which executes a string (or code in other format) as if it were a statement; in some languages, such as Python, both ...
In Unix-like operating systems, true and false are commands whose only function is to always return with a predetermined exit status.Programmers and scripts often use the exit status of a command to assess success (exit status zero) or failure (non-zero) of the command.
In computing, Bash (short for "Bourne Again SHell,") [6] is an interactive command interpreter and command programming language developed for UNIX-like operating systems. [7] Created in 1989 [ 8 ] by Brian Fox for the GNU Project , it is supported by the Free Software Foundation and designed as a 100% free alternative for the Bourne shell ( sh ...
Application programs may also implement a command-line interface. For example, in Unix-like systems, the telnet program has a number of commands for controlling a link to a remote computer system. Since the commands to the program are made of the same keystrokes as the data being sent to a remote computer, some means of distinguishing the two ...
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).
Performing one-liners directly on the Unix command line can be accomplished by using Python's -cmd flag (-c for short), and typically requires the import of one or more modules. Statements are separated using ";" instead of newlines. For example, to print the last field of unix long listing:
Single-line, when instructions are instruction 1 : instruction 2 : ...: If condition Then instructions «Else instructions» If condition Then instructions ElseIf condition Then instructions... «Else instructions» End If Single-line: See note about C-like languages; the Else clause of a single-line If statement can contain another single-line ...