Transcript Perl - Tel Aviv University

Regular Expressions
Regular Expression (or pattern) in Perl – is a template
that either matches or doesn’t match a given string.
Regular Expressions in Perl:
if( $str =~ /hello/){
while( <STDIN> ){
if( /hello/ ){
…
…
}
@words = split /\s+/, $str;
}
}
Regular Expressions (2)
Regular Expressions in Unix:
grep “include .*h”
regular
expression
*.h
 globes
Regular Expressions (3)
“.” matchs any char except a newline \n
/hello.you/ matches any string that has ‘hello’, followed
by any one (exactly one) character, followed by ‘you’.
/to*ols/ last character before ‘*’ may be repeated zero
or more times. Matches ‘tools’,’tooooools’,’tols’ (but not
‘toxols’ !!!)
/to+ols/ ------//------- one or more -----//------.
/to.*ols/ matches ‘to’, followed by any string, followed
by ‘ols’.
/to?ols/ the character before ‘?’ is optional. Thus, there
are only two matching strings – ‘tools’ and ‘tols’.
Regular Expressions (4)
Grouping – parentheses ‘( )’ are used for grouping one
or more characters.
/(tools)+/ matches “toolstoolstoolstools”.
Alternatives:
/hello (world|Perl)/ - matches “hello world”, “hello
Perl”.
Regular Expressions (5)
Character Class
/Hello [abcde]/ matches “Hello a” or “Hello b” …
/Hello [a-e]/
the same as above
Negating:
[^abc]
any char except a,b,c
Regular Expressions (6)
Shortcuts
• \d digit
• \w word character [A-Za-z0-9_]
• \s white space
Negative ^ –
[^\d] matches non digit
Regular Expressions (7)
Quantifiers:
/a{3,6}/ - matches “a” repeated 3,4,5,6 times
/(abc){3,}/
- matches three or more repetitions of “abc”.
/a{3}/ - matches exactly three repetitions of “a”.
*
=
{0,}
+
=
{1,}
?
=
{0,1}
Regular Expressions (8)
/^abc/ - “^” beginning of a string
Anchors
/a\^bc/ - matches “\^”
/[^abc]/ - negating
^ - marks the beginning of the string
$ - marks the end of the string
/^Hello Perl/ - matches “Hello Perl, good by Perl”, but not “Perl Hello Perl”
/^\s*$/ - matches all blank lines
Regular Expressions (9)
\b - matches at either end of a word (matches the
start or the end of a group of \w characters)
/\bPerl\b/ - matches “Hello Perl”, “Perl”
but not “Perl++”
\B - negative of \b
Regular Expressions (10)
Backreferences:
/(World|Perl) \1/ - matches “World World”, “Perl
Perl”.
/((hello|hi) (world|Perl))/
•\1 refers to (hello|hi) (world|Perl)
•\2 refers to (hello|hi)
•\3 refers to (world|Perl)
Examples
1. What is it?
/^0x[0-9a-fA-F]+$/
2. Date format: Month-Day-Year -> Year:Day:Month
$date = “12-31-1901”;
$date =~ s/(\d+)-(\d+)-(\d+)/$3:$2:$1/;
Examples
3. Make a pattern that matches any line of input that
has the same word repeated two or more times in a
row. Whitespace between words may differ.
Example 3
1. /\w+/
#matches a word
2. /(\w+)/
#to remember later
3. /(\w+)\1+/
#two or more times
4. /(\w+)(\s+\1)+/ #whitespace between
words
5. “This is a test” -> /\b(\w+)(\s+\1)+/
6. “This is the theory” ->
/\b(\w+)(\s+\1)+\b/
Regular Expressions (11)
$&
$`
$’
- what really was matched
- what was before
- the rest of the string after the matched pattern
$` . $& . $’ - original string
Regular Expressions (12)
Substitutions:
s/T/U/; #substitutes T with U (only once)
s/T/U/g; #global substitution
s/\s+/ /g; #collapses whitespaces
s/(\w+) (\w+)/$2 $1/g;
s/T/U/; #applied on $_ variable
$str =~ s/T/U/;
Split and Join
$str=“aaa bbb
ccc
dddd”;
@words = split /\s+/, $str;
$str = join ‘:‘, @words;
#result is “aaa:bbb:ccc:dddd”
@words = split /\s+/, $_; “ aaa b” -> “”, “aaa”, “b”
@words = split;
“ aaa b” ->
“aaa”, “b”
@words = split ‘ ‘, $_;
“ aaa b” ->
“aaa”, “b”
Grep
grep EXPR, LIST;
@results = grep /^>/, @array;
@results = grep /^>/, <FILE>;
CGI - Common Gateway Interface
CGI – a standard that defines the protocol between
a web server and a application (script).
Web
Browser
http/
ssl …
DB
Web Server
Application
search example
Sending information to CGI
Two ways to submit information:
•HTML form
<form action="/cgi-bin/scilib.pl" method=POST>
<input type=text name=searchj value="">
<input type=submit value="search">
</form>
•With URL
http://www.tau.ac.il/cgi-bin/scilib.pl?searchj=protein
CGI - Simple script
#!/usr/bin/perl
use CGI qw(:standard);
print header;
$param= param('formtext');
print "<hr><p align=left>Hello CGI: $param";
print end_html;
HomeWork
Write a CGI Perl script that prints IP address of
submitted server name. Input is received from HTML text
box. (you need to create two pages - (1) html page with the
text box (2) cgi script that receives and prints the IP
address.)
See: http://www.cs.tau.ac.il/faq/home.html
HomeWork (2)
Input/Output Examples:
[maxshats@nova ~]$ ping -c 1 -w 3 tau.ac.il
ping: unknown host tau.ac.il
[maxshats@nova ~]$ ping -c 1 -w 3 www.cnn.com
PING cnn.com (207.25.71.25) from 132.67.128.249 : 56(84)
bytes of data.
--- cnn.com ping statistics --4 packets transmitted, 0 packets received, 100% packet loss
Use regular expression
HomeWork (3)
Run Unix commands:
$str=`ping -c 1 -w 3 www.cnn.com`;
print $str;
Debugger
On Unix: “perldoc perldebug”
Invoke Perl with the -d switch:
perl –d your_code.pl arg1 arg2 …
Debugger (2)
•always displays the line it's about to execute
•Any command not recognized by the debugger is
directly executed (eval'd) as Perl code (for
example you can print out some variables).
p expr (as “print expr”)
x expr - Nested data structures are printed out
recursively, unlike the real print function in Perl
Debugger (3)
s [expr]
Single step. Executes until the beginning of another statement,
descending into subroutine calls. If an expression is supplied that
includes function calls, it too will be single-stepped.
n [expr]
Next. Executes over subroutine calls, until the beginning of the
next statement. If an expression is supplied that includes
function calls, those functions will be executed with stops before
each statement.
<CR>
Repeat last n or s command.
Debugger (4)
r
Continue until the return from the current
subroutine.
c [line|sub]
Continue, optionally inserting a one-time-only
breakpoint at the specified line or subroutine.
w [line]
List window (a few lines) around the current/[line]
line
Debugger (5)
b subname [condition]
b [line] [condition]
Set a breakpoint before the given line. If line is
omitted, set a breakpoint on the line about to be
executed. If a condition is specified, it's evaluated each
time the statement is reached: a breakpoint is taken
only if the condition is true. Breakpoints may only be set
on lines that begin an executable statement.
b 237 $x > 30
b 237 ++$count237 < 11
b 33 /pattern/i
Debugger (6)
W expr
Add a global watch-expression.