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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 it on a tree with any empty folders, at

  set files [glob "$current/*"]

but that problem may be overcome with a catch:

  if {[catch {set files [glob "$current/*"]}]} {
    set $files ""
  }


Updated code [here].

There's a second catch withn our example too - where the code checks for the file size, it's necessary to catch the file size if it might be used on a "special" such as a socket, pipe or device file.

From our Tcl Programming course as run last week.

(written 2015-10-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T214 - Tcl/Tk - Other Facilities in Tcl
  [4762] Coverage map in Tcl - how many times has each proc been called? - (2017-09-28)
  [4525] What does Tcl do if you try to run a command that is not defined? - (2015-10-10)
  [4207] Exception handling in Tcl - (2013-11-14)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [3570] Trapping errors in Tcl - the safety net that catch provides - (2012-01-06)
  [3287] Exceptions - Tcl style - (2011-05-12)
  [2467] Tcl - catching an error before your program crashes - (2009-10-22)
  [1338] Handling Binary data in Tcl (with a note on C) - (2007-09-09)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1277] AgtInvoke - a command to drive Agilent Tcl software extensions - (2007-07-26)
  [782] Converting between Hex and Decimal in Tcl - (2006-06-28)
  [748] Getting rid of variables after you have finished with them - (2006-06-06)
  [461] Shortened interactive commands - (2005-10-11)
  [366] Error handling in Tcl through catch - (2005-07-02)
  [364] pu daily and p hourly - (2005-06-30)
  [239] What and why for the epoch - (2005-03-08)

T209 - Tcl/Tk - File and Directory Handling
  [4524] Tcl - a new example for data reformatting - (2015-10-10)
  [4461] Reading from a URL, and reading Json, from your Tcl script - (2015-03-12)
  [3617] The fileutil package and a list of file system commands in Tcl - (2012-02-18)
  [3429] Searching through all the files in or below a directory - Ruby, Tcl, Perl - (2011-09-09)
  [3320] Reading the nth line from a file (Perl and Tcl examples) - (2011-06-09)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [1467] stdout v stderr (Tcl, Perl, Shell) - (2007-12-10)
  [1426] Buffering up in Tcl - the empty coke can comparison - (2007-11-10)
  [1407] Reading from another process in Tcl (pipes and sockets) - (2007-10-26)
  [785] Running external processes in Tcl and Tcl/Tk - (2006-06-29)
  [779] The fragility of pancakes - and better structures - (2006-06-26)


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Course Schedule - October 2015 to June 2016
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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