Files and Directory
chdir ("/etc") change to directory /etc
@a= </etc/*>; @a gets list of files in /etc [glob]
@a</etc/h*>; @a gets a list of h* files in /etc [glob]
while ($v=<bin/*> {
@a = ~s/.*\/// remove path (before last slash-- greedy)
opendir (ETC,"/etc") || die "Cannot open dir/etc";
@a-readdir(ETC);
close (ETC); [dir handle see man readdir]
unlink ("file6"); remove file6 (like unix rm file6)
unlink ("*.c"); like rm*.c (also takes lists and variables)
rename (("top","bot") || die "Cannot rename top to bot.";
rename ("f","bin/f"); mv, but must repeat file name in destination
link ("hat","cap"); Unix In hat cap
symlink ("hat","cap"); Unix In-s hat cap
Sx-readlink ("file"); returns name of symlink or undef (zero)
mkdir ("bin",0777) || die "cannot make dir bin" (x-1 w-2 r-4];
rmdir ("bin") die "cannot remove dir bin";
chmod (0666,"f1","12") Change permissions for files fl and f2
System Processing
system ("who"); executes the shell process "who"
system ("who >file") && die "cannot create file right now"; return of true (nonzero) is an error -
opposite of Perl therefore && instead
of ||
while (system ("grep aa fl"))} executes the shell process "grep"
push (@a, $_)} puts found lines in array @a
while (system ("grep", "aa", "fl")) {same except list saves one shell process; therefore faster}
push (@a, $_)}
Sv=`grep aa fl`; "backtics' execute the shell process "grep"
foreach (`grep aa fl`) { puts found line in array @a
push (@a, $_);}
Regular Expressions
if (/abc/) { search for string "abc"; print line which "abc" occurs; S_ is the default
variable
print "$_";
which () { diamond operator: this routine is like grep
if (/abc/) {
print "S_";} search for "abc" from a file or files
/ca*t/ matches "ca" any number of "a's" and "t" matches any character but \n
/c.*?t/ the? suppresses greedy: cat but not cattt any char from present to end of
the line
s/cat/dogs/ search "cat" substitute "dogs"
s/cat/dogs/g search every "cat" on a line, sub "dogs"
s/cAT/dogs/1 ignore case for search
[Aa] match big or little A
[^A] anything but A
[0-9] every single digit
[a-zA-Z0-9] any single letter or digit
[d] digits, every digit; same as [0-0]
[\D] anything not \d; same as [^0-9]
[\w] words; same as [a-zA-Z0-9]
[\W] same as [^a-zA-Z0-9]; any nonword char
[\s] white space; same as [\r\t\n\f]
[\S] same as [^\r\t\n\f]
[a+] one or more a's in sequence (aaaaaa)
[a?] zero or one a
[a*] zero or more a's in sequence
$="a bbbbb c";
s/b*/cat/; replaces bbbbb with cat "a cat c"
s/b{4}/cat/; replaced 4 b's with cat: "a catb c"
s/b (3.7}/cat/; replaces 3 to 7 b's: "a cat c" (greedy)
s/ant(.)/bug\1/ \1 gets paren value (12 gets second paren) if ants then bugs; if anto then
bugo (second parens referenced with \2)
/read|writ/ing/ alternative match (*reading or writing)
\b word boundary
/cat\b/ "cat" but not "catalog"f
/\bcat\ "catalog" but not "concatenate"
/\bcat\b/ cat as a word, but not in a word
/^a/ matches a if a is first char in string
/a$/ matches a if a is last char in string
/a|b+/ match one or any number of b's
/(a|b)+/ match any number of a's or b's
$a="real food";
$x=Sa=/(.)\1/; Sx is 1 (true): matches oo in "food"
$a=s/oo/ee/ oo changed to ee; $a is now "real feed";
$1,$2,53 /1/2 /3 etc can be accessed as $1 $2 $3..
$_=" they cannot write at all";
/w..te/;` matches "write"
print S'; $' prints "they cannot"
print $&; $& prints "write"
print $'; $' prints "at all"
srand
$n=rand(35) Set $n to real number 0-34
$x-@v[rand (35)] $x gets random element 0-34 of @v
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Hashes (Associative Arrays)
%map = ("pete", "xx"", "jo", "yy", "ida", "zz") create associative array (pairs of values)
$map{pete} recalls xx with key "pcte" [note curly brackets]
$map{jo} recalls yy with key "jo"
$map {me} = "aa" creates key "me" with value "aa"
$var{date} = 94 creates "date" with value of 94
@x = %map @x gets ("pete", "xx", "jo","y"ida", "zz", "me", "aa")
%w=@x creates assoc.array from @x
keys(%map) lists keys of %map (e.g. use with foreach) in a scalar context returns no. of keys
each(%map) lists all current values of %map
delete $map{jo} deletes key and value; retuns the value
foreach (keys(%map)) {print ("$map{$_}\s");}
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String Fanctions
chop($str) discards any last char of $str
chomp($str) discards \n if last char of $str
$v= chop($str) puts last char in $v
str eq str compares two strings (true if equal)
$var eq "this" compare contents of var with str "this"
ne, It, gt, le, ge, cmp (returns -1, 0, or 1) these are the other string operators
$str="ab" x 4; $str is now "abababab"
. concatenate two strings
.= concatenation assignment strings
($var=~/reg. ex./) retuns true if regular expressions found
($var =~ /^Pe/i) regular expression starts "pe", any case
$var -~s/ab/cd/; substitute -- all ab to cd (like sed)
$var =~tr/A-Z/a-z/; translate - all $var to lowercase; like Unix tr
$count = tr/a-z//; no change but counts no. of lowercase letters
$var= tr/a-z/ /c c complement: changes any but a-z to space
$var=tr/a-z/ABC/d delete: deletes any match ofa-z that is not abc
$v = index($str,$x) find index no of beginning string $x in $str
$v=("abc", "bc") $v gets 1; position of "a" is 0 (zero)
$y - rindex($str,$x) index starts from right, but numbers from left
$v = ("cabc", "c") $v gets 3; position of first c from right
$v = substr($str, $start, $length) $v gets substring if found
$start is index of string;$length is no of char
$v=substr("cabc",1,3)returns “abc"; 3 ($length) could be omirted here
$v = substr("cabc",-3,3) retums "abc"; negative counts back from right
$str = "big boat"; initialize $str;
substr($str,-4) ="payments"; $str becomes "big payments"
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Print
$v = sprintf("%10s \n", $str); $v gets print string: like printf
printf "hello\n" Prints "hello" to standard out
printf ("%20s %4d %6.2f\n", $s, $i, $r); Same as "C" printf; %20s for string, 4d for decimal
integer, %6.2f for floating point.
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Variable and Arrays
$var = "contents" initialize a scalar variable
$v=45 value of $v is 45
($a,$b,$c)=(2,4,6) $a is 2, $b is 4, $c is 6
(1..5) same as (1,2,3,4,5)
($a,$b) = ($b,$a) swap $a and $b
($d,@list) = ($a,$b,$c) $d gets value of Sa, array @listgets valuc of $b and $c
@var = ("xx", "yy", "zz") initialize an array variable
$var[0] recalls "xx"
$var[1] recalls "yy"
$#var index of last item (2 for @var)
@v= (1,2,3) initialize @v (for following examples)
@w = (0,@v,4,five) @w is now (0,1,2,3,4,five)
@w=(six,@w) @w is now (six,0,1,2,3,4,five)
$b=$w[1] $b is now 0
$b= ++$w[1] $b and $w[1] are now 1
$b=$w[1]++ $b is still 1 and $w[1] is now 2
@c=@w[0,1,6] @c is now (six,2,five)
@w[0,1] = (no,no) @w is now (no,no,1,2,3,4,five)
$w[$#w] returns "five" (the last element)
print "@w[0..$#w]" prints entire &rray
push(@v,$b) adds new element $b to (right) end of @v
pop(@v) removes last (rightmost) element of @v
chop(@v) removes last char from each element
unshift(@v,Sb) adds new clement $b to front of @v
shift(@v) removes first element of @v
reverse(@v) returns order of clements reversed
sort(@v) returns elements sorted (string sort)
@v=sort{$a<=>$v}@v uses a mumeric sort
@v = (0,1,2,) initialize @v (for following examples)
push(@v,6) @v is now (0,1,2,6)
$b = pop(@v) @v is now (0,1,2,);$b is 6
unshift(@v,$b) @v is now (6,0,1,2)
$b = shift(@v) @v is now. (0,1,2,) $b gets 6 again
@x=reverse(@v) @x is (2,1,0); @v is still (0,1,2)
@v = (2,3,1,11) initialize@v
@v = sort(@v) @v is now (1,11,2,3,) (string sort!)
@v=(aa,bb,cc) initialize@v
chop(@v) @v is now (a,b,c,)[array context]
split(/separator/list) change string into array at separators;
$a = "crazy-cool-cats"; @c = split (/-/,$a); @c becomes ("crazy", "cool", "cats")
$_= "big blue bugs" @bugs = split $_ and whitespace defaults
join(separator, array) change array into string with separators
$b=join("::",@c) $b beçomes ("crazy::cool::cats"); any or nochars as separators, but no reg
expressions
Control Operators
sub do_it { creates subroutine with local varsSv and @a
local ($v,@a);
$v=1} subroutine returns last expression evaluated
local($v,$w)=@_; special char@_ assigns locals from parameters,
elements $_[0],$_[1},$_[2],etc
&&do_it cats 5 do_it invoked with arguments(cats and 5)
if(expr){ if expr is true then list1 executed
statement list1
} elsif (expr2) { else if expr2 is true then list2 executed
statement list2 (can continue with more elsifs)
} else {
statement list3 else--when all the aboves fail execute this list3
}
expr2 if expr; if statement with order reversed
(same for unless, while, and until)
this && that; logic and; equals: if (this) {that}
this || that; logic or; equals: unless (this) {that}
if (/a/ && /e/ && /i/ && /o/ &&/u/) {print "all vowels used";}
all comditions must be true for true;
logical "and"
unless (cxpr) { executes unless expr is true statement list}
statement list } takes elsif and else (like if)
while(expr) { while expr is true repest execution of statement list
statement list}
until (expr) {. like while, but stops.when expr is true
statement list}
for (ini, test,incr) { initialize a variable, test to run list,
statement list} then increment the variable
for ($a=1; $a≤=10; $a++) { priat"$a";} Prints 1 through 10
for ($a=1; $a<=$#var,Sa++) {print "$a";} 1 through length @var-1
foreach $v (@list){ Repeats cmd list for cach $v produced
statement list by@list; NOTE:If you change any particular
} $v, the element changes in the array @list
@w=(1..9);
foreach $v(@w) { prints 1 through 9 on separate lines print $vin;}
print $v\n;}
@w=(1..9); Omits the $v;Perl assumes the default variable $_
foreach (@w){
print$_;}
last ends loops:while,for,etc.
next skips to next item in loop-while,for,etc.
redo jumps to top of loop; unlike next it doesn't
get new item; use with last to break loop
LABEL7: label statements for next and last jumps
for jumping out of nested loop to outer loop
last LABEL7 end nested labeled LABEL7
die "no such file"; ends program; prints message to stdout
File Operators
ореn (FL, "fl"); open input file fl with filehandle FL
while(<FL>){} puts next line from file fl into $_
close(FL) closes file fl
open (OUT,">fl"); open file for output with filehandle OUT
open (AP,">>fl"); open file fl for append,filehandle AP
open (MAIL, " | mail fred@clarkson.edu");
| Piping rums command -- here the mail cmd
[put piping at end to grab cmd output|]
dbmopen (%var, "fl", 0666); keeps array %var in file fl
$var {$name} =time; appends time to array in fl
dbmclose(%var); 0666 sets octal file permissions
rename ($fl, "$fl.ex") renames file to file.ex
<STDIN> waits for Iceyboard input -- adds \n
<STDOUT>
<STDERR>
$v=<STDIN> $v gets single line input on Enter
@v=<STDIN> @v several lines; ^D to end (array context)
while (<STDIN>) { reads each line to $_
print "$_";} $_is the default variable
while(<>){ diamond operator reads @ARGV from the
print$_;} cmd line(here it prints all lines of arg files)
File Test (list is not exhaustive)
$fl="filename" assigns a filename to a variable
if(-r $fl && -w_) Underline "_" reports on a -w without
{print "use $fl" ;} a new stat system call.
-r readable (file or dir)
-w writable
-x executable
-o owned by user
-e exists
-z zero size (file exists)
-s non zero size
-f file
-d directory
-l symlink
-T text file
-B binary file
-M modification age in days
-A acess age in days
stat() remaining info on files
String Escapes for Double Quotes
\n newline
\t tab
\007 octal value (007= beli)
\x7f hex value (7f = delete)
\$ literal dollar sign
\l lowercase the next letter
\L lowercase letters until \E
\u uppercase next letter
\U uppercase letters until \E
