CSC 4630

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CSC 4630

• Perl 1

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Perl

• Practical Extraction and Support Language
• A glue language under UNIX
• Written by Larry Wall
• Claimed to be the most portable of scripting
  languages
• See www.perl.com

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Perl by Example

• Perl is more powerful than awk, but looks
  somewhat the same.
• Perl is more flexible than shell scripts, but
  uses some of the same constructs.
• Perl is based on C, and in fact the interpreter
  is written in C, but is easier to use than C.

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Perl by Example (2)

• Beginning assumptions and notations
• Statements are terminated by (semicolon)
• Comments start anywhere on a line with and end
  at the end of the line. Thus, you can write
  explanations on the line for the line. But they
  cant be two line explanations.
• Built-in functions neither require nor forbid
  ( ) around their arguments

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Perl by Example (3)

• First line of Perl program should be a directive
  to the interpreter e.g. (either)
• ! /opt/local/bin/perl w
• ! /usr/bin/perl w
• Invoke by perl ltfilenamegt or ltfilenamegt
• Scalar variables have names that start with and
  have values that are either strings or double
  precision real numbers.

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Exercise 1

• ! /opt/local/bin/perl w
• print (Hello, world!\n)

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Exercise 2

• ! /opt/local/bin/perl w
• print What is your name?
• name ltSTDINgt
• chomp (name)
• print Hello, name!\n

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Exercise 3

• !/opt/local/bin/perl w
• print What is your name?
• name ltSTDINgt
• chomp (name)
• if (name eq Randal)
• print Hello, name! Glad youre here\n
• else
• print Hello, name!\n ordinary greeting

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Exercise 4

• ! /opt/local/bin/perl w
• secretword llama the secret word
• print What is your name?
• chomp(name ltSTDINgt)
• if (name eq Randal)
• print Hello, name! Glad youre here\n
• else
• print Hello, name!\n
• print What is the secret word?
• chomp(guess ltSTDINgt)
• while (guess ne secretword)
• print Wrong, try again. Secret word?
• chomp(guess ltSTDINgt)

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Non-scalar Variables

• For example, arrays
• Identifier starts with an _at_
• Can be initialized with a list of strings
• _at_words (camel, llama, alpaca)
• Or with the qw operator (which saves keystrokes)
• _at_words qw (camel llama alpaca)
• Elements accessed as scalars, so
• words0 is camel, words1 is llama
• NB Index origin is 0
• i 2 wordsi has value alpaca

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Exercise 5

• !/opt/local/bin/perl w
• _at_swords qw (camel llama alpaca) set multiple
  secret words
• print What is your name?
• chomp(name ltSTDINgt)
• if (name eq Randal)
• print Hello, name! Glad youre here\n
• else
• print Hello, name!\n
• print What is the secret word?
• chomp(guess ltSTDINgt)
• i 0 index in swords array
• correct maybe status of search
• while (correct eq maybe)
• if(guess eq swordsi) correct yes
  set flag on success
• elsif (i lt 2) i not success, try
  next secret word
• else
• print Wrong, try again. Secret word?
  no word matches, ask again
• chomp(guess ltSTDINgt)
• i0 reset index in secret word array

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Scalar operators

• Numeric - /
• Numeric comparison lt lt gt gt !
• String . (for concat) x (for multiple
  concat)
• String comparison lt le eq ge gt ne
• Identifier ltlettergt ltletter digit under gt
  
• Assignment
• (carries value of expression)
• binary assignment . etc.
• increment prefix, postfix i i
• increment then assign vs. assign then increment