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An existence check before reading a file can catch and/or prevent a fatal error, for instance. For that reason, most programming language libraries contain a means of checking whether a file exists. An existence check can sometimes involve a " brute force " approach of checking all records for a given identifier, as in this Microsoft Excel ...
ON ERROR GOTO handler OPEN "Somefile.txt" FOR INPUT AS # 1 CLOSE # 1 PRINT "File opened successfully" END handler: PRINT "File does not exist" END ' RESUME may be used instead which returns control to original position.
Expect is an extension to the Tcl scripting language written by Don Libes. [2] The program automates interactions with programs that expose a text terminal interface. Expect, originally written in 1990 for the Unix platform, has since become available for Microsoft Windows and other systems.
In computer programming, several language mechanisms exist for exception handling. The term exception is typically used to denote a data structure storing information about an exceptional condition. One mechanism to transfer control, or raise an exception, is known as a throw ; the exception is said to be thrown .
The Tcl programming language was created in the spring of 1988 by John Ousterhout while he was working at the University of California, Berkeley. [14] [15] Originally "born out of frustration", [11] according to the author, with programmers devising their own languages for extending electronic design automation (EDA) software and, more specifically, the VLSI design tool Magic, which was a ...
The reason is that in Tcl, curly braces are not used only to delimit functions as in C or Java. More generally, curly braces are used to group words together into a single argument. [ 10 ] [ 11 ] In Tcl, the word while takes two arguments, a condition and an action .
Tk is a platform-independent GUI framework developed for Tcl. From a Tcl shell (tclsh), Tk may be invoked using the command package require Tk. The program wish (WIndowing SHell) provides a way to run a tclsh shell in a graphical window as well as providing Tk. [16] Tk has the following characteristics: Platform-independent: Like Tcl, Tk is ...
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 ...