1/12 Steven Leung Very Basic Perl Tricks A Few Ground Rules File I/O and Formatting Operators, Flow Control Statements Regular Expression Subroutines Hash (Associative Arrays) Built-in Functions Miscellaneous

2/12 Steven Leung Very Basic Perl Tricks A Few Ground Rules All scalar variables start with $ Regular array as a Element is $name[index], where index is a numeric value, default starting index is 0, define-able thru $]. $#name returns the last index of the array name ($] -1 if undefined) Hash (associative array) as a whole: %name Element of %name is $name { key }, where key is a string value The keys operator returns a regular array containing all the keys All variables are global variables, unless declared explicitly with the local operator Scalar, array, hash, file handle, and subroutine names have separate name spaces The default operand of pattern matching, IO operations, and most (but not all) of the built-in functions is $_

3/12 Steven Leung Very Basic Perl Tricks A Few Ground Rules (cont.) It is legal to reference a variable before it gets a value assigned. When evaluated, a variable without a value assigned has the value of undefined, which will evaluate to false logically. Use the defined operator to distinguish 0(or ) and undefined Variables in … (…) will (not) be substituted with its value Same as shell interpretation Functions can be chained together, and the evaluation (following the LISP convention) started from the right and the results feed back to the left function An evaluation can produce results of different types. The exact type returned depends on the context, i.e., the data type expected by the assignment or function argument

4/12 Steven Leung Very Basic Perl Tricks File I/O Predefined file handler: STDIN, STDOUT, STDERR open(F, my_file) # Open my_file for read while ( ) {... } # Read a line thru F to $_ <> is the readline operator open(O, >my_ofile) # Open my_ofile for write print O this,, that,, whatever\n; No comma between O (the file handler) and the rest If O is omitted, the default is STDOUT printf and sprintf accept a string to specify format, same as in C E.g. printf O (%s %d, $string, $num); Pipes can be added to the filename part: open(F, pwd|);

5/12 Steven Leung Very Basic Perl Tricks Output Formatting format name $var1, $var2, $var3, $var4. # default name is STDOUT left, center, right justified fixed-point number Format statement must be ended with a. at the 1 st col. of a new line. Format is executed by the write command foreach { # set up $var1, $var2, $var3, $var4 write; } Use select(File_Handler); $~ = Format_Name ; to switch format

6/12 Steven Leung Very Basic Perl Tricks Operators, Flow Control Stmts C-Like Operators: ++, ||, &&, +=, … For numeric: ==, !=,, =, For strings: eq, ne, lt, gt, le, ge, cmp, =~ (see Reg. Expr.) File test: -e, -f, -d,... If (expr) { … } [ [elsif (expr) { … }] else { … } ] while (expr) { … } while (<>) {... } # Same as while ($_= ) {... } foreach [$var] { … } foreach (<>) {... } # Read in the whole file first for (expr; expr; expr) { … } for ($i=1; $i<=10; $i++) {... } last, next while (<>) { next if /^#/;... last if /^END/ }

7/12 Steven Leung Very Basic Perl Tricks Regular Expression Characters that have special meanings in / pattern /: () [ ]. - + * ? ^ $ \ | / Short-hand notation of often-used regular expressions: \d digit \D Not \d \s white space \S Not \s \w alphanumeric + _ \W Not \w Pattern matching operator =~ [expr =~] [m]/Pattern/[i] # Just check if pattern found [$var =~] s/Pattern/Replace/[g][i][e] # Substitution [$var =~] tr/Search_list/Repl_list/ # Translate Examples $str =~ /^\s*module\s+(\w+)/; ($cell, $inst) = $str =~ /^\s*(\w+)\s+(\S+)/; ($cell, $inst) = $str =~ /^\s*(\w+)\s+([^\s,\(]+)/;

8/12 Steven Leung Very Basic Perl Tricks Subroutines Defining a subroutine sub my_func { local($a, $b, $c) # Code to process $a $b $c return($some_val); # } Calling the subroutine my_func $ret_val = &my_func($x, $y, $z); Note that arguments ($x, $y, $z) are passed to the subroutine through the Anonymous subroutine examples foreach $n (sort {$a cmp {... } $a and $b are values passed to the anonymous sub by sort func foreach (sort {$dly{$b} $dly{$a}} keys %dly) {... } cmp/ compares by alphabetical/numeric order

9/12 Steven Leung Very Basic Perl Tricks Hash (Associative Array) Think about hash as a 2-column table keyvalue INVX117.0 AND2X125.5 SDFFX %area_of Name of the hash (table) Keys are of string typeValues are of scalar type (numeric/string) The values are accessed by $name{key} Example: $area_of{$cell_type} Function keys returns a regular array (list) of all keys Common use of hash table as a flag on an array of obj. Example: if (!$seen{$cell_type}++) {... }

10/12 Steven Leung Very Basic Perl Tricks Build-In Functions (Most Used) chop [$str] # Chop off the last char from $str split[(/pat/,$str)] split $str into an array with /pat/ as field separator # append the LIST # shift the 1 st element out grep(EXPR, LIST) Return an array of elements from LIST for which EXPR is true = grep(!$seen{$_}++, values %cell_of); warn LIST # print LIST to STDERR die LIST # print LIST to STDERR, then exit open(F, infile) || die *** Cant open infile\n; exec/system(LIST) # non-/blocking system call

11/12 Steven Leung Very Basic Perl Tricks Miscellaneous 1 st line: #!/usr/local/bin/perl Command line args are set to built-in Useful command line switches -[p|n]e perl statements Both p,n wrap the statements with while (<>) {... } -p also print $_ after the statements -i : in-place editing Use qq/q to change double/single quote character print qq|Pcap = $pincap_of{$cell_of{$inst}:$pin}\n|; Other useful special variables $0: Name of the perl script file from the command line $`, $&, $ : preceding, matching, and following strings Pattern matching of /\([^\)]+\)/ on line: abc ( 123, 321 ) xyz $` = abc, $& = ( 123, 321 ), $ = xyz

12/12 Steven Leung Very Basic Perl Tricks Version 5.2 ;... DESIGN bloom ;... COMPONENTS ; - bloom_top|cmem|..|U204 ANDX1 ; - bloom_top|regs|..|U31 XOR2X2 ;... END COMPONENTS... bloom.def Exercise Write the get_cell_stat script for the following input/output % get_cell_stat bloom.def > bloom.cell_stat Cell Count Perc Acc NANDX INVX bloom.cell_stat get_cell_stat