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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Reactive (dynamic) formatting in Perl

If you want to format your data neatly in columns, you can use sprintf or printf to do so if you're using a fixed width font. A format of "%20s", for example, calls for a string that's 20 characters long and will be trailing space padded ... except ...that figure "20" is a minimum width, and if your text is longer, the output line will also be longer!

There are two possible solutions you can apply. The first is to use a format of the form "%20.20s" which says "make it 20 wide and TRUNCATE the string to 20 characters if it's longer" ... which might be fine in some circumstances, but eliminate vital data in others. The second solution is to use dynamic formatting. Here's how it works

a) Look through all the data that has to go into a particular field, and note the longest string's length

$longhost = 1;
foreach $host (keys %counter) {
  if (length($host) > $longhost) {$longhost = length($host); }
}


b) Use the variable that contains that longest string's length within the format string:

printf("%-${longhost}s ",$host);

There's a complete program showing this (with comments too, to explain things like the ${var} notation) here.

Further new samples this morning ...

An introductory example to hashes
Modifiers and comments in Perl regular expressions
Looking up data in a file from a web page
(written 2008-10-31)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P602 - Perl - Advanced File and Directory Handling
  [839] Reporting on the 10 largest files or 10 top scores - (2006-08-20)
  [975] Answering ALL the delegate's Perl questions - (2006-12-09)
  [1225] Perl - functions for directory handling - (2007-06-09)
  [1709] There is more that one way - Perl - (2008-07-14)
  [1832] Processing all files in a directory - Perl - (2008-10-11)
  [2876] Different perl examples - some corners I rarely explore - (2010-07-18)
  [3412] Handling binary data in Perl is easy! - (2011-08-30)
  [3429] Searching through all the files in or below a directory - Ruby, Tcl, Perl - (2011-09-09)

P207 - Perl - File Handling
  [12] How many people in a room? - (2004-08-12)
  [114] Relative or absolute milkman - (2004-11-10)
  [255] STDIN, STDOUT, STDERR and DATA - Perl file handles - (2005-03-23)
  [616] printf - a flawed but useful function - (2006-02-22)
  [618] Perl - its up to YOU to check your file opened - (2006-02-23)
  [702] Iterators - expressions tha change each time you call them - (2006-04-27)
  [867] Being sure to be positive in Perl - (2006-09-15)
  [1312] Some one line Perl tips and techniques - (2007-08-21)
  [1416] Good, steady, simple example - Perl file handling - (2007-10-30)
  [1442] Reading a file multiple times - file pointers - (2007-11-23)
  [1467] stdout v stderr (Tcl, Perl, Shell) - (2007-12-10)
  [1841] Formatting with a leading + / Lua and Perl - (2008-10-15)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [2233] Transforming data in Perl using lists of lists and hashes of hashes - (2009-06-12)
  [2405] But I am reading from a file - no need to prompt (Perl) - (2009-09-14)
  [2818] File open and read in Perl - modernisation - (2010-06-19)
  [2821] Chancellor George Osborne inspires Perl Program - (2010-06-22)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [3326] Finding your big files in Perl - design considerations beyond the course environment - (2011-06-14)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3830] Traversing a directory in Perl - (2012-08-08)
  [3839] Spraying data from one incoming to series of outgoing files in Perl - (2012-08-15)


Back to
Seven new intermediate Perl examples
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or
Horse's mouth home
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Remember your units
Some other Articles
Debugging and Data::Dumper in Perl
Object Oriented Perl - First Steps
About dieing and exiting in Perl
Remember your units
Reactive (dynamic) formatting in Perl
Wiltshire at dawn - the tourist trail
Camera with night vision, youth with no vision
November and December Public Course Schedule
A few of my favourite things
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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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