perl :
1)Print a Message to the Terminal
#vi message.plprint "When that Aprill with his shoures soote\n";
print "The droghte of March ath perced to the roote,\n";
print "And bathed every veyne in swich licour\n";
print "Of which vertu engendered is the flour...\n";
:x
getting out put:
#perl message.pl
When that Aprill with his shoures soote
The droghte of March ath perced to the roote,
And bathed every veyne in swich licour
Of which vertu engendered is the flour...
2) math operations
#vi math.pl
print "2 + 2 =", 2+2, "\n";
print "log(1e23)= ", log(1e23), "\n";
print "2 * sin(3.1414)= ", 2 * sin(3.1414), "\n";
#perl math.pl
2 + 2 =4
log(1e23)= 52.9594571388631
2 * sin(3.1414)= 0.000385307177203065
3) Run a System Command
#vi system.pl
system "ls";
4)Return the Time of Day
$time = localtime;print "The time is now $time\n"; //even in double codes $time will prints time and day of month
RUNNING PERL IS OF TWO OPTIONS
option 1)perl time.pl
option 2)vi time.pl
#!/usr/bin/perl // add this line at first
# file: time.pl // optional
$time = localtime;
print "The time is now $time\n";
#chmod +x time.pl
#./time.pl
Useful Perl Command-Line Options
You can call Perl with a few command-line options to help catch errors:
-c Perform a syntax check, but don't run.
-w Turn on verbose warnings.
-d Turn on the Perl debugger.
like perl -cw time.pl or simply add #!/usr/bin/perl -w line at beginning of the program.
PERL STATEMENTS:
statement is a command that is recognized by the Perl interpreter and executed. Statements are terminated by the semicolon character (;). They are also usually separated by a newline character to enhance readability.
EXAMPLE
$sum = 2 + 2; # this is a statement
$f =; $g = $f++; # these are two statements
$g = $f
/
$sum; # this is one statement, spread across 3 lines
blocks
{ # block starts
my $EcoRI = 'GAATTC';
my $sequence = ;
print "Sequence contains an EcoRI site" if $sequence=~/$EcoRI/;
} # block ends
my $sequence2 = ;
if (length($sequence) < length = ",length($sequence),"> Labeled Blocks
You can also attach a label to a block of statements like this:
READ_SEQUENCE: { #this is my lable
$sequence =
print "length = ",length($sequence),"\n";
}
This is sometimes useful for controlling nested loops.
Literals
Literals are constant values that you embed directly in the program code. Perl supports both string literals and numeric literals.
The difference between single and double-quoted strings is that variables and certain special escape codes are interpolated into double quoted strings, but not in single-quoted ones.\040 Octal character (octal 040 is the space character)
\0x2a Hexadecimal character (hex 2A is the "*" character)
\cA Control character (This is the ^A character)
\u Uppercase next character
\l Lowercase next character
\U Uppercase everything until \E
\L Lowercase everything until \E
\Q Quote non-word characters until \E
\E End \U, \L or \Q operation
ex:-
"She cried \"Oh dear! The parakeet has flown the coop!\"";
# evaluates to: She cried "Oh dear! The parakeet has flown the coop!"
Numeric Literals
You can refer to numeric values using integers, floating point numbers, scientific notation, hexadecimal notation, and octal. With some help from the Math::Complex module, you can refer to complex numbers as well:
-1.23; # a negative floating point number
1_000_000; # you can use _ to improve readability
1.23E45; # scientific notation
0x7b; # hexadecimal notation (decimal 123)
0173; # octal notation (decimal 123)
use Math::Complex; # bring in the Math::Complex module
12+3*i; # complex number 12 + 3i
Backtick Strings
You can also enclose a string in backtics (`). This has the unusual property of executing whatever is inside the string as a Unix system command, and returning its output:
`ls -l`;
# evaluates to a string containing the output of running the
# ls -l command
Lists
The last type of literal that Perl recognizes is the list, which is multiple values strung together using the comma operator (,) and enclosed by parentheses. Lists are closely related to arrays, which we talk about later.
like:-
('one', 'two', 'three', 1, 2, 3, 4.2);
# this is 7-member list contains a mixure of strings, integers
# and floats
operators :
Numeric & String Operators.
The "." operator acts on strings. The "!" operator acts on strings and numbers. The rest act on numbers.
| Operator | Description | Example | Result |
|---|---|---|---|
| . | String concatenate | 'Teddy' . 'Bear' | TeddyBear |
| = | Assignment | $a = 'Teddy' | $a variable contains 'Teddy' |
| + | Addition | 3+2 | 5 |
| - | Subtraction | 3-2 | 1 |
| - | Negation | -2 | -2 |
| ! | Not | !1 | 0 |
| * | Multiplication | 3*2 | 6 |
| / | Division | 3/2 | 1.5 |
| % | Modulus | 3%2 | 1 |
| ** | Exponentiation | 3**2 | 9 |
| File input | Read a line of input from standard input | ||
| >> | Right bit shift | 3>>2 | 0 (binary 11>>2=00) |
| << | Left bit shift | 3<<2 | 12 (binary 11<<2=1100) |
| | | Bitwise OR | 3|2 | 3 (binary 11|10=11 |
| & | Bitwise AND | 3&2 | 2 (binary 11&10=10 |
| ^ | Bitwise XOR | 3^2 | 1 (binary 11^10=01 |
Logical Operators
These operators compare strings or numbers, returning TRUE or FALSE:
| Numeric Comparison | String Comparison | ||
|---|---|---|---|
| 3 == 2 | equal to | 'Teddy' eq 'Bear' | equal to |
| 3 != 2 | not equal to | 'Teddy' ne 'Bear' | not equal to |
| 3 <> | less than | 'Teddy' lt 'Bear' | less than |
| 3 > 2 | greater than | 'Teddy' gt 'Bear' | greater than |
| 3 <= 2 | less or equal | 'Teddy' le 'Bear' | less than or equal |
| 3 >= 2 | greater than or equal | 'Teddy' ge 'Bear' | greater than or equal |
| 3 <=> 2 | compare | 'Teddy' cmp 'Bear' | compare |
| 'Teddy' =~ /Bear/ | pattern match | ||
The <=> and cmp operators return:
- -1 if the left side is less than the right side
- 0 if the left side equals the right side
- +1 if the left side is greater than the right side
File Operators
Perl has special file operators that can be used to query the file system. These operators generally return TRUE or FALSE.
Example:
print "Is a directory!\n" if -d '/usr/home'; |
There are many of these operators. Here are some of the most useful ones:
| -e filename | file exists |
|---|---|
| -r filename | file is readable |
| -w filename | file is writable |
| -x filename | file is executable |
| -z filename | file has zero size |
| -s filename | file has nonzero size (returns size) |
| -d filename | file is a directory |
| -T filename | file is a text file |
| -B filename | file is a binary file |
| -M filename | age of file in days since script launched |
| -A filename | same for access time |
Functions
In addition to its operators, Perl has many functions. Functions have a human-readable name, such as print and take one or more arguments passed as a list. A function may return no value, a single value (AKA "scalar"), or a list (AKA "array"). You can enclose the argument list in parentheses, or leave the parentheses off.
A few examples:
# The function is print. Its argument is a string. |
Often Used Functions (alphabetic listing)
For specific information on a function, use perldoc -f function_name to get a concise summary.
| abs | absolute value |
|---|---|
| chdir | change current directory |
| chmod | change permissions of file/directory |
| chomp | remove terminal newline from string variable |
| chop | remove last character from string variable |
| chown | change ownership of file/directory |
| close | close a file handle |
| closedir | close a directory handle |
| cos | cosine |
| defined | test whether variable is defined |
| delete | delete a key from a hash |
| die | exit with an error message |
| each | iterate through keys & values of a hash |
| eof | test a filehandle for end of file |
| eval | evaluate a string as a perl expression |
| exec | quit Perl and execute a system command |
| exists | test that a hash key exists |
| exit | exit from the Perl script |
| glob | expand a directory listing using shell wildcards |
| gmtime | current time in GMT |
| grep | filter an array for entries that meet a criterion |
| index | find location of a substring inside a larger string |
| int | throw away the fractional part of a floating point number |
| join | join an array together into a string |
| keys | return the keys of a hash |
| kill | send a signal to one or more processes |
| last | exit enclosing loop |
| lc | convert string to lowercase |
| lcfirst | lowercase first character of string |
| length | find length of string |
| local | temporarily replace the value of a global variable |
| localtime | return time in local timezone |
| log | natural logarithm |
| m// | pattern match operation |
| map | perform on operation on each member of array or list |
| mkdir | make a new directory |
| my | create a local variable |
| next | jump to the top of enclosing loop |
| open | open a file for reading or writing |
| opendir | open a directory for listing |
| pack | pack a list into a compact binary representation |
| package | create a new namespace for a module |
| pop | pop the last item off the end of an array |
| print to terminal or a file | |
| printf | formatted print to a terminal or file |
| push | push a value onto the end of an array |
| q/STRING/ | generalized single-quote operation |
| qq/STRING/ | generalized double-quote operation |
| qx/STRING/ | generalized backtick operation |
| qw/STRING/ | turn a space-delimited string of words into a list |
| rand | random number generator |
| read | read binary data from a file |
| readdir | read the contents of a directory |
| readline | read a line from a text file |
| readlink | determine the target of a symbolic link |
| redo | restart a loop from the top |
| ref | return the type of a variable reference |
| rename | rename or move a file |
| require | load functions defined in a library file |
| return | return a value from a user-defined subroutine |
| reverse | reverse a string or list |
| rewinddir | rewind a directory handle to the beginning |
| rindex | find a substring in a larger string, from right to left |
| rmdir | remove a directory |
| s/// | pattern substitution operation |
| scalar | force an expression to be treated as a scalar |
| seek | reposition a filehandle to an arbitrary point in a file |
| select | make a filehandle the default for output |
| shift | shift a value off the beginning of an array |
| sin | sine |
| sleep | put the script to sleep for a while |
| sort | sort an array or list by user-specified criteria |
| splice | insert/delete array items |
| split | split a string into pieces according to a pattern |
| sprintf | formatted string creation |
| sqrt | square root |
| stat | get information about a file |
| sub | define a subroutine |
| substr | extract a substring from a string |
| symlink | create a symbolic link |
| system | execute an operating system command, then return to Perl |
| tell | return the position of a filehandle within a file |
| tie | associate a variable with a database |
| time | return number of seconds since January 1, 1970 |
| tr/// | replace characters in a string |
| truncate | truncate a file (make it smaller) |
| uc | uppercase a string |
| ucfirst | uppercase first character of a string |
| umask | change file creation mask |
| undef | undefine (remove) a variable |
| unlink | delete a file |
| unpack | the reverse of pack |
| untie | the reverse of tie |
| unshift | move a value onto the beginning of an array |
| use | import variables and functions from a library module |
| values | return the values of a hash variable |
| wantarray | return true in an array context |
| warn | print a warning to standard error |
| write | formatted report generation |
Creating Your Own Functions
You can define your own functions or redefine the built-in ones using the sub function. This is described in more detail in a later.
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