Exercises, examples and other material relating to training module T209. This topic is presented on public courses Learning to program in Tcl, Tcl Programming, Tcl Programming

This module covers opening, reading and writing files in Tcl. You'll also learn how to check the contents of directories, test for the existence of individual files, and look up other information ranging from file size to file update time.

Articles and tips on this subject		updated
4524	Tcl - a new example for data reformatting Tcl is an excellent language for combing through and reformatting data - though rarely a first choice language for such tasks if users aren't doing other things with it too. Towards the end of last week's Learning to program in TCL course, a "side task" requirement came up to reformat our course diary ...	2015-10-10
4523	Catching failed commands and not crashing the program in Tcl Where a command may fail in Tcl (causing Tcl to crash), you can defer it within a catch command. That will return a true value if it fails, and an optional extra parameter gives you the associated error message. A program to look for the biggest file in or below a directory [here] fails if you run ...	2015-10-10
4461	Reading from a URL, and reading Json, from your Tcl script You can read from a URL in Tcl using the http package ... for example   package require http   set handle [::http::geturl http://www.wellho.co.uk/robots.txt] And you can then collect the data:   set body [::http::data $handle] and the http status code:   set ...	2015-03-15
3617	The fileutil package and a list of file system commands in Tcl On top of the file commands, the ::fileutil package which is shipped with Tcl includes a range of commonly used structures ("design patterns") which means you don't have to keep wring your own composites. Here is a combined list, sorting them out by category rather than by which command or package they ...	2012-02-18
3429	Searching through all the files in or below a directory - Ruby, Tcl, Perl Many of our customers want to learn how to traverse all the files in a directory, or perhaps even all the files in or below a directory. I quite often write a demonstration program during our courses which looks though part of a file system tree for files over a certain size, or for the largest (so ...	2011-09-09
3320	Reading the nth line from a file (Perl and Tcl examples) "How do I find the 100th line in a file" - a common question for newcomers to coding. The short answer is to open the file, and loop through to read lines until the one that you want. Although most languages have a seek command or function, that works by bytes and with a typical text / ascii file, ...	2011-06-09
3192	Tcl - Some example of HOW TO in handling data files and formats During the Tcl course I was running earlier this week, we got involved in a number of interesting topics such as • How to clean up input lines into lists of fields (use split) • How to reformat awkward fields (use regexp and regsub) • How to combine files that vary in format from year ...	2011-03-04
1407	Reading from another process in Tcl (pipes and sockets) If you want to read from another process on the same system that you're running your code on in Tcl can be done using a pipe - you can use open with the command name instead of the file name, preceeded by a pipe character (|) - thus: set said [open |df r]   while {[gets $said this] >= 0} {   puts ...	2011-03-01
2467	Tcl - catching an error before your program crashes There are times when a Tcl command can fail because of the data being passed in to it ... and when it fails, it can do so with a spectacular crash! For example, the glob command which matches files to a pattern (Tcl's ls or dir if you like to think of it that way) can go 'belly up' if there are no files ...	2009-10-22
1467	stdout v stderr (Tcl, Perl, Shell) When you're programming, you shouldn't write code to read directly from the keyboard and write to the screen .... what if you want to have your program read from or write to a file sometimes? Instead, you should write code to read from stdin (Tcl) or STDIN (Perl) and write to stdout (Tcl) or STDOUT ...	2007-12-12
1426	Buffering up in Tcl - the empty coke can comparison A comment on buffering in Tcl .... if {1 == 0} { When you finish drinking a can of Coke, you don't call your local recycling plant up straight away and have them send a truck around to collect the empty - that would be inefficient to put it mildly. And in the same way, a computer doesn't always save ...	2007-11-10
779	The fragility of pancakes - and better structures Have you ever hunted around a directory for a file ... you KNOW it's there, but you can't find it - can't see the wood for the trees, if you like, in a listing that spills over many pages? I call such directory structures "pancakes" as they're thin and flat, and they tend not to be very easy to work ...	2006-06-30
785	Running external processes in Tcl and Tcl/Tk If you want to run external processes from a Tcl based program (Tcl, Tcl/Tk, expect), there are various ways of doing it. Firstly, the whole purpose of the Expect extension is to allow you to control other processes via its three major commands of spawn which starts another process, send which sends ...	2006-06-30

bigbelow	Find biggest file in or below a specified folder
bigbelow.v2	biggest below - practical example that traps empty folders
biggest	using glob to check all files in a directory
diary	diary data for for_qa script
disc_status	Piping input from an operating system command
dnstab	Read a file, extract from it
failer	Using catch to trap file open failures
files	fileutil package in use
filework	Report file statuses
for_qa.tcl	Data reformatting example / course end tie together
multifile	Output to stdout and several files at the same time
rail	Data extraction and reporting from multiple files
recent	List all files modified in the last hour

Tcl is a great Engineer's language