Perl Reference Card 1.3 Hashes 4 System Interaction This is version 2 of the perl reference card. %h=(k1 => “val1”,k2 => 3); hash initialization system(“cat $f|sort -u>$f.s”); system call (cl) 2008 Michael Goerz . $val = $map{k1}; recall value @a = readpipe(“lsmod”); catch output http://www.physik.fu-berlin.de/~goerz/ @a = %h; array of keys and values Information taken liberally from the perl documentation and various other sources. $today = “Today: “.`date`; catch output You may freely distribute this document. %h = @a; create hash from array chroot(“/home/user/”); change root foreach $k (keys(%h)){..} iterate over list of keys while (<*.c>) {} operate on all c-files foreach $v (vals(%h)){..} iterate over list of values unlink(“/tmp/file”); delete file while (($k,$v)=each %h){..} iterate over key-value-pairs if (-f “file.txt”){...} file test 1 Variable Types delete $h{k1}; delete key File Tests: exists $h{k1} does key exist? -r, -w readable, writeable 1.1 Scalars and Strings defined $h{k1} is key defined? -x executable chomp($str); discard trailing \n -e exists $v = chop($str); $v becomes trailing char -f, -d, -l is file, directory, symlink eq, ne, lt, gt, le, ge, cmp string comparison -T, -B text file, binary file $str = “0” x 4; $str is now “0000” 2 Basic Syntax -M, -A mod/access age in days $v = index($str, $x); find index of $x in $str, ($a, $b) = shift(@ARGV); read command line params @stats = stat(“filename”); 13-element list with status $v = rindex($str, $x); starting from left or right sub p{my $var = shift; ...} define subroutine More: chmod, chown, chroot, fcntl, glob, ioctl, link, $v = substr($str, $strt, $len); extract substring p(“bla”); execute subroutine lstat, mkdir, opendir, readlink, rename, rmdir, $cnt = $sky =~ tr/0-9//; count the digits in $sky if(expr){} elsif {} else {} conditional symlink, umask, utime $str =~ tr/a-zA-Z/ /cs; change non-alphas to space unless (expr){} negative conditional $v = sprintf(“%10s %08d”,$s,$n); format string while (expr){} while-loop Format String: %[flags][0][width][.precision][mod]type until (expr){} until-loop types: do {} until (expr) postcheck until-loop 5 Input/Output c character for($i=1; $i<=10; $i++){} for-loop open(INFILE,"in.txt") or die; open file for input d(i) signed decimal int foreach $i (@list){} foreach-loop open(INFILE,"<:utf8","file"); open file with encoding e(E) scientific notation last, next, redo end loop, skip to next, jump to top open(TMP, "+>", undef); open anonymous temp file f decimal floating point eval {$a=$a/$b; }; exception handling open(MEMORY,'>', \$var); open in-memory-file g, G shorter %e or %f / %E or %f warn $@ if $@; open(OUT,">out.txt") or die; open output file o signed octal open(LOG,">>my.log") or die; open file for append s string of chars open(PRC,"caesar <$file |"); read from process u, x, X unsigned decimal int / hex int / hex int in caps open(EXTRACT, "|sort >Tmp$$"); write to process p address pointer 3 References and Data Structures $line = ; get next line n nothing printed $aref = \@a; reference to array @lines = ; slurp infile modifiers: h,l,L arg is short int / long int, double/ long double $aref = [1,"foo",undef,13]; anonymous array foreach $line (){...} loop of lines from STDIN More: chr, crypt, hex, lc, lcfirst, length, oct, ord, $el = $aref->[0]; access element of array print STDERR "Warning 1.\n"; print to STDERR pack, q/STRING/, qq/STRING/, reverse, uc, ucfirst $el = @{$aref}[0]; close INFILE; close filehandle $aref2 = [@{$aref1}]; copy array More: binmode, dbmopen, dbmclose, fileno, flock, 1.2 Arrays and Lists $href = \%h; reference to hash format, getc, read, readdir, readline, rewinddir, @a = (1..5); array initialization $href ={APR => 4,AUG => 8}; anonymous hash seek, seekdir, select, syscall, sysreed, sysseek, $el = $href->{APR}; access element of hash $i = @a; number of elements in @a tell, telldir,truncate, pack, unpack, vec $el = %{$href}{APR}; ($a, $b) = ($b, $a); swap $a and $b $href2 = {%{$href1}}; copy hash $x = $a[1]; access to index 1 if (ref($r) eq "HASH") {} checks if $r points to hash $i = $#a; last index in @a @a = ([1, 2],[3, 4]); 2-dim array 6 Regular Expressions push(@a, $s); appends $s to @a $i = $a[0][1]; access 2-dim array ($var =~ /re/), ($var !~ /re/) matches / does not match $a = pop(@a); removes last element %HoA=(fs=>["f","b"], hash of arrays m/pattern/igmsoxc matching pattern chop(@a); remove last char (per el.) sp=>["h","m"]); qr/pattern/imsox store regex in variable $a = shift(@a); removes first element $name = $HoA{sp}[1]; access to hash of arrays s/pattern/replacement/igmsoxe search and replace reverse(@a); reverse @a $fh = \*STDIN globref Modifiers: @a = sort{$ela <=> $elb}(@a); sort numerically $coderef = \&fnc; code ref (e.g. callback) i case-insensitive o compile once @a = split(/-/,$s); split string into @a $coderef =sub{print "bla"}; anon subroutine g global x extended $s = join(“, ” @c); join @a elements into string &$coderef(); calling anon subroutine m multiline c don't reset pos (with g) @a2 = @a[1,2,6..9]; array slice sub createcnt{ my $c=shift; closure, $c persists s as single line (. matches \n) e evaluate replacement @a2 = grep(!/^#/, @a); remove comments from @a return sub { print "$c++"; }; } *foo{THING} foo-syntax for creating refs Syntax: Extended Constructs 8 One-Liners \ escape (?#text) comment -0 (zero) specify the input record separator . any single char (?imxs-imsx:...) enable or disable option -a split data into an array named @F ^ start of line (?=...), (?!...) positive / negative look-ahead -F specify pattern for -a to use when splitting $ end of line (?<=..), (?...) prohibit backtracking -n run through all the @ARGV arguments as files, using <> +, +? 1 or more times (greedy / nongreedy) (?{ code }) embedded code -p same as -n, but will also print the contents of $_ ?, ?? 0 or 1 times (greedy / nongreedy) (??{ code }) dynamic regex \b, \B word boundary ( \w - \W) / match except at w.b. (?(cond)yes|no) condition corresponding to captured parentheses Interactive Mode: perl -de 42 \A string start (with /m) (?(cond)yes) condition corresponding to look-around Variables \Z string end (before \n) Examples: $& entire matched string \z absolute string end 1. just lines 15 to 17, efficiently $` everything prior to matched string \G continue from previous m//g perl -ne 'print if $. >= 15; exit if $. >= 17;' $' everything after matched string [...] character set 2. just lines NOT between line 10 and 20 $1, $2 ... n-th captured expression (...) group, capture to $1, $2 perl -ne 'print unless 10 .. 20' $+ last parenthesis pattern match (?:...) group without capturing 3. lines between START and END $^N most recently closed capt. {n,m} , {n,m}? at least n times, at most m times perl -ne 'print if /^START$/ .. /^END$/' $^R result of last {n,} , {n,}? at least n times (?{...}) 4. in-place edit of *.c files changing all foo to bar {n} , {n}? exactly n times @-, @+ offsets of starts / ends of groups perl -pi.bak -e 's/\bfoo\b/bar/g' *.c | or 5. delete first 10 lines \1, \2 text from nth group ($1, ...) perl -i.old -ne 'print unless 1 .. 10' foo.txt Escape Sequences: 6. change all the isolated oldvar occurrences to newvar \a alarm (beep) \e escape 7 Object-Oriented Perl and Modules perl -i.old -pe 's{\boldvar\b}{newvar}g' *.[chy] \f formfeed \n newline 7. printing each line in reverse order \r carriage return \t tab Defining a new class: perl -e 'print reverse <>' file1 file2 file3 .... \cx control-x \l lowercase next char package Person; 8. find palindromes in the /usr/dict/words dictionary file use strict; \L lowercase until \E \U uppercase until \E perl -lne '$_ = lc $_; print if $_ eq reverse' sub new { #constructor, any name is fine \Q diable metachars until \E \E end case modifications /usr/dict/words my $class = shift; Character Classes: 9. command-line that reverses all the bytes in a file my $self = {}; [amy] 'a', 'm', or 'y' perl -0777e 'print scalar reverse <>' f1 f2 f3 $self->{NAME} = undef; # field [f-j.-] range f-j, dot, and dash 10. word wrap between 50 and 72 chars $self->{"_CENSUS"} = \$Census; # class data [^f-j] everything except range f-j perl -p000e 'tr/ \t\n\r/ /; ++ ${ $self->{"_CENSUS"} }; \d, \D digit [0-9] / non-digit s/(.{50,72})\s/$1\n/g;$_.="\n"x2' bless ($self, $class); \w, \W word char [a-zA-Z0-9_] / non-word 11. strip and remove double spaces return $self; perl -pe '$_ = " $_ "; tr/ \t/ /s; $_ = char } \s, \S whitepace [ \t\n\r\f] / non-space substr($_,1,-1)' sub name { #method 12. move '*.txt.out' to '*.out' \C match a byte my $self = shift; \pP, \PP match p-named unicode / non-p-named-unicode perl -e '($n = $_) =~ s/\.txt(\.out)$/$1/ and not if (@_) { $self->{NAME} = shift } -e $n and rename $_, $n for @ARGV' * \p{...}, \P{...} match long-named unicode / non-named-unicode return $self->{NAME}; \X match extended unicode } Posix: sub DESTROY { #destructor [:alnum] alphanumeric my $self = shift; -- ${$self->{"_CENSUS"} };} [:alpha] alphabetic 1; # so the ‘require’ or ‘use’ succeeds [:ascii:] any ASCII char [:blank:] whitespace [ \t] Using the class: [:cntrl:] control characters use Person; [:digit:] digits $him = Person->new(); [:graph:] alphanum + punctuation $him->name("Jason"); [:lower:] lowercase chars printf "There's someone named %s.\n", $him->name; [:print:] alphanum, punct, space use Data::Dumper; print Dumper($him); # debug [:punct:] punctuation [:space:] whitespace [\s\ck] [:upper:] uppercase chars [:word:] alphanum + '_' [:xdigit:] hex digit [:^digit:] non-digit Installing Modules: perl -MCPAN -e shell;