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notes:perl_cheat_sheet [2026/06/13 10:38]
114.119.135.37 old revision restored (2026/05/23 12:38) 		notes:perl_cheat_sheet [2026/06/13 23:41] (current)
216.73.217.104 old revision restored (2026/06/12 14:56)
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   * Comments start with # (no block comments)   * Comments start with # (no block comments)
   * Parenthesis are optional unless part of syntax.   * Parenthesis are optional unless part of syntax.
 +  * ''@ARGV'' contains arguments, $0 contains program name.
 +  * ''die''/''warn'' can be used to exit/warn, $! will contain any system error message. Without \n at the end, perl will append line number to error message.
  
 ===== Numbers ===== ===== Numbers =====
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   * List functions may return different scalars - array variables return number of elements. The ''scalar'' function forces a scalar context e.g. for print function.   * List functions may return different scalars - array variables return number of elements. The ''scalar'' function forces a scalar context e.g. for print function.
  
 +===== Hashes =====
 +
 +  * A hash is a list indexed by a string (key) - a collection of key-value pairs. ''%hash'' has its own namespace.
 +  * Uses scalable, efficient algorithms. Used to be called associative arrays.
 +  * ''$hash{$some_key}'' to access a value (curly-braces instead of square braces).
 +  * Assigning a hash to an array unwinds (flattens) it. 
 +  * To initialize a hash :<code perl>%some_hash = ('a', 1, 'b', 2, 'c', 3);
 +%some_hash = ( 'a' => 1, 'b'=>2, 'c'=>3,);</code>
 +  * When using an arrow (a fat-comma), simple keys don't have to be quoted (barewords) .
 ===== Control Structures ===== ===== Control Structures =====
  
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   * ''<>'' iterates over all files in @ARGV (or STDIN if no args) like e.g. cat/sed/awk. <code perl>while (<>) {   * ''<>'' iterates over all files in @ARGV (or STDIN if no args) like e.g. cat/sed/awk. <code perl>while (<>) {
     chomp;     chomp;
-    print "It was $_ that I saw!\n";+    print LOGFILE "It was $_ that I saw!\n";
 }</code> }</code>
 +  * ''print'' takes list of items and sends all to STDOUT (unseparated). ''print @array;'' vs ''print "@array";'' <code perl>print <>;          # source code for 'cat'
 +print sort <>;     # source code for 'sort'</code>
 +  * C-like printf function %g for number auto-format,%10s, %-10d etc.<code perl>my @items = qw( wilma dino pebbles );
 +my $format = "The items are:\n" . ("%10s\n" x @items);
 +printf $format, @items;
 +printf "The items are:\n".("%10s\n" x @items), @items;
 +</code>
 +  * Filehandles can be barewords (upper-cased) or variables. Special filehandles are : STDIN, STDOUT, STDERR, DATA, ARGV, and ARGVOUT .<code perl>open CONFIG, '<dino';  # < is optional
 +open BEDROCK, '>fred' || die "Cannot open fred: $!";
 +open LOG, '>>:encoding(UTF-8)','logfile'; # for perl >= 5.6
 +open my $bedrock, '>:crlf', $file_name; # DOS-formatted output
 +binmode STDOUT, ':encoding(UTF-8)';</code>
 +  * ''select'' can be used to change default output filehandle. ''$| = 1;'' unbuffers currently selected output.
 ===== User Subroutines ===== ===== User Subroutines =====
  
notes/perl_cheat_sheet.1781372294.txt.gz · Last modified: 2026/06/13 10:38 by 114.119.135.37 · Currently locked by: 43.110.34.247

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