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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
P207 - Perl - File Handling
  [3839] Spraying data from one incoming to series of outgoing files in Perl - (2012-08-15)
  [3830] Traversing a directory in Perl - (2012-08-08)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3326] Finding your big files in Perl - design considerations beyond the course environment - (2011-06-14)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [2821] Chancellor George Osborne inspires Perl Program - (2010-06-22)
  [2818] File open and read in Perl - modernisation - (2010-06-19)
  [2405] But I am reading from a file - no need to prompt (Perl) - (2009-09-14)
  [2233] Transforming data in Perl using lists of lists and hashes of hashes - (2009-06-12)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1841] Formatting with a leading + / Lua and Perl - (2008-10-15)
  [1709] There is more that one way - Perl - (2008-07-14)
  [1467] stdout v stderr (Tcl, Perl, Shell) - (2007-12-10)
  [1442] Reading a file multiple times - file pointers - (2007-11-23)
  [1416] Good, steady, simple example - Perl file handling - (2007-10-30)
  [1312] Some one line Perl tips and techniques - (2007-08-21)
  [867] Being sure to be positive in Perl - (2006-09-15)
  [702] Iterators - expressions tha change each time you call them - (2006-04-27)
  [618] Perl - its up to YOU to check your file opened - (2006-02-23)
  [616] printf - a flawed but useful function - (2006-02-22)
  [255] STDIN, STDOUT, STDERR and DATA - Perl file handles - (2005-03-23)
  [114] Relative or absolute milkman - (2004-11-10)
  [12] How many people in a room? - (2004-08-12)

P602 - Perl - Advanced File and Directory Handling
  [3429] Searching through all the files in or below a directory - Ruby, Tcl, Perl - (2011-09-09)
  [3412] Handling binary data in Perl is easy! - (2011-08-30)
  [2876] Different perl examples - some corners I rarely explore - (2010-07-18)
  [1832] Processing all files in a directory - Perl - (2008-10-11)
  [1225] Perl - functions for directory handling - (2007-06-09)
  [975] Answering ALL the delegate's Perl questions - (2006-12-09)
  [839] Reporting on the 10 largest files or 10 top scores - (2006-08-20)


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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
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