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notes:perl_cheat_sheet

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notes:perl_cheat_sheet [2026/06/12 11:45]
114.119.152.46 old revision restored (2026/05/24 07:47) 		notes:perl_cheat_sheet [2026/06/13 20:45] (current)
37.122.190.32 old revision restored (2026/05/23 12:38)
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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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   * Expressions parsed in either a scalar context or a list context. Scalars are promoted to single-element lists in list context.    * Expressions parsed in either a scalar context or a list context. Scalars are promoted to single-element lists in list context. 
   * 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 a big arrow (a fat-comma) or when accessing a value, simple keys don't have to be quoted (barewords) e.g. <code perl>%some_hash = ( a => 1}; $some_hash{a};</code> 
-  * ''%revhash = reverse %hash'' to reverse a hash (for non-unique values, last one wins). 
-  * ''keys %hash;'' and ''values %hash;'' return a list of keys or value in same order (or # of keys/values in scalar context). 
-  *  '' %hash'' is true only if hash has at least one key-value pair. 
-  * To iterate over hash : <code perl>while ( ($key, $value) = each %hash ) { 
-  print "$key => $value\n"; }</code> or in order of keys <code perl>foreach $key (sort keys %hash) { 
-  print "$key => $hash{$key}\n"; } </code> 
-  * %ENV hash holds environment variables. 
  
 ===== 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 LOGFILE "It was $_ that I saw!\n";+    print "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.1781289904.txt.gz · Last modified: 2026/06/12 11:45 by 114.119.152.46

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