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    perl-pocket perl-pocket Document Transcript

    • A Brief Pocket Reference for Perl Programming This pocket reference was created to help the author to refresh Perl, presumably aiming at an intermediate programmer or advanced. This pocket reference is mainly based on several anonymous resources found on the Internet. It’s free to distribute/modify. Any inquiry should be mailed to joumon@cs.unm.edu. o Perl - starts with #!/usr/bin/per or with a proper path - each statement ends with ; - run with –d for debugging - run with –w for warning - comment with # - case-sensitive o Scalar Variables - start with $ - use ‘my’ ex) $var = 3; my $greet = “hello?” - $_ : default variable for most operations - @ARGV : arguments array - @_ : argument array to functions and access with $_[index] - use local for a local variable in a function o Operators - +/-/*///%/**/./x/=/+=/-=/.= - single-quote and double-quote ex) “hello”.”world” --> “helloworld” “hello”x2 --> “hellohello” $var = 3; print “hi$var”; --> “hi3” print ‘hi$var’; --> “hi$var” - strings enclosed in single quotes are taken literally - strings enclosed in double quotes interpret variables or control characters ($var, n, r, etc.) o Arrays - declare as @name=(elem1, elem2, ...); ex) my @family = (“Mary”, “John”) $family[1] --> “John” push(@family, “Chris”); --> push returns length my @wholefamily = (@family, “Bill”); push(@family, “Hellen”, “Jason”) push(@family, (“Hellen”, “Jason”));
    • push(@wholefamily, @family); $elem=pop(@family) --> pos returns an element $len=@family --> set length $str=”@family” --> set to string ($a, $b) = ($c, $d) ($a, $b) = @food; --> $a is the first element and $b is the rest (@a, $b) = @food; --> $b is undefined print @food; print “@food”; print @food.””; - use $name[index] to index - index starts from zero - $#array returns index of last element of an array, i.e. n-1 o File Handling - use open(), close() ex) $file=”hello.txt”; open(INFO, $file); while(<INFO>) {...} # or @lines = <INFO>; close(INFO); - use <STDIN>,<STDOUT>,<STDERR> ex) open(INFO, $file); # Open for input open(INFO, ">$file"); # Open for output open(INFO, ">>$file"); # Open for appending open(INFO, "<$file"); # Also open for input open(INFO, '-'); # Open standard input open(INFO, '>-'); # Open standard output - use print <INFO> ... o Control Structures - foreach $var (@array) {...} - for(init; final; step) {...} - while (predicate) {...} - do {...} while/until (predicate); - comparison operators: ==/!=/eq/ne - logical operators: ||/&&/! - if (predicate) {...} elsif (predicate) {...} ... else {...} - if (predicate) {...}: if predicate is missing, then $_ is used o Regex - use =~ for pattern matching - use !~ for non-matching ex) $str = “hello world”
    • $a =~ /hel/ --> true $b !~ /hel/ --> false - if we assign to $_, then we could omit $_ ex) $_ =”hello” if (/hel/) {...} - substitution: s/source/target/ - use g for global substitution and use i for ignore-case ex) $var =~ s/long/LONG/ s/long/LONG/ # $_ keeps the result - use $1, $2, ..., $9 to remember ex) s/^(.)(.*)(.)$/321/ - use $`, $&, $’ to remember before, during, and after matching ex) $_ = "Lord Whopper of Fibbing"; /pp/; $` eq "Lord Wo"; # true $& eq "pp"; # true $' eq "er of Fibbing"; #true $search = "the"; s/$search/xxx/g; - tr function allows character by character translation ex) $sentence =~ tr/abc/edf/ $count = ($sentence =~ tr/*/*/); # count tr/a-z/A-Z/; # range o More Regex -. # Any single character except a newline - ^ # The beginning of the line or string - $ # The end of the line or string - * # Zero or more of the last character - + # One or more of the last character -? # Zero or one of the last character - [qjk] # Either q or j or k - [^qjk] # Neither q nor j nor k - [a-z] # Anything from a to z inclusive - [^a-z] # No lower case letters - [a-zA-Z] # Any letter - [a-z]+ # Any non-zero sequence of lower case letters - jelly|cream # Either jelly or cream - (eg|le)gs # Either eggs or legs - (da)+ # Either da or dada or dadada or... - n # A newline - t # A tab - w # Any alphanumeric (word) character. # The same as [a-zA-Z0-9_] - W # Any non-word character. # The same as [^a-zA-Z0-9_]
    • - d # Any digit. The same as [0-9] - D # Any non-digit. The same as [^0-9] - s # Any whitespace character: space, # tab, newline, etc - S # Any non-whitespace character - b # A word boundary, outside [] only - B # No word boundary - | # Vertical bar - [ # An open square bracket - ) # A closing parenthesis - * # An asterisk - ^ # A carat symbol - / # A slash - # A backslash - {n} : match exactly n repetitions of the previous element - {n,} : match at least n repetitions - {n,m} : match at least n but no more than m repetitions o Miscellaneous Functions - chomp()/chop()/split()/shift()/unshift() o Functions - sub FUNC {...} - parameters in @_ - the result of the last thing is returned