Differences

This shows you the differences between two versions of the page.

--- notes:perl_cheat_sheet [2026/06/11 19:34]
114.119.145.205 old revision restored (2013/09/11 16:44)
+++ notes:perl_cheat_sheet [2026/06/13 14:55] (current)
47.245.90.216 old revision restored (2026/06/04 13:11)
@@ Line 13: / Line 13: @@
   * Comments start with # (no block comments)
   * Parenthesis are optional unless part of syntax.
+  * ''@ARGV'' contains arguments, $0 contains program name.
 ===== Numbers =====
@@ Line 82: / Line 83: @@
   * Read a line of input - ''$line = <STDIN>;''
   * ''chomp'' removes a newline e.g. ''chomp($line=<STDIN>);''
-  * Assigning <STDIN> to a list reads all input up till EOF e.g. <code perl> chmop(@lines = <STDIN>);</code>
+  * Assigning <STDIN> to a list reads all input up till EOF e.g. <code perl> chomp(@lines = <STDIN>);</code>
+  * Loop over input ($_ can only be used in this specific case) <code perl>while (<STDIN>) {
+    print "I saw $_";
+}</code>
+  * ''foreach'' can also be used but uses more memory since it reads all input into memory first.
+  * ''<>'' iterates over all files in @ARGV (or STDIN if no args) like e.g. cat/sed/awk. <code perl>while (<>) {
+    chomp;
+    print "It was $_ that I saw!\n";
+}</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 BEDROCK, '>:crlf', $file_name; # DOS-formatted output
+binmode STDOUT, ':encoding(UTF-8)';</code>
 ===== User Subroutines =====
@@ Line 91: / Line 111: @@
   $m + $n;
 } </code>
-  * The value of the last expression evaluated is returned.
+  * The value of the last expression evaluated is returned. But ''return $a;'' can be used to return immediately.
+  * A list can be returned if the subroutine is called in a list context (''wantarray'' can be used to detect list or scalar context).
   * Arguments are in the list @_ . If ''&mysub;'' is used, the parent's argument list is inherited.
   * Lexical scoped variables can be used in any block by prefixing with ''my''.
+  * In Perl 5.10 and up ''state $x;'' can be used to declare a private variable that keep state between calls.
+  * Ampersand is optional if subroutine has previously been declared or if parenthesis are used. Ampersand is not optional if built-in subroutine is being overridden.

DokuWiki

Site Tools

Differences

Page Tools