|
1. Arguments
2. Array
3. Codes
4. Commands
5. Hash
6. File
7. Function
8. Operator
9. Pattern matching
10. Processes
11. String
12. Tricks
1.1. Getting arguments
The allowed parameters are listed calling getopts().
If the parameter is followed by ':', a supplementary argument is required.
use Getopt::Std;
my %switch = ();
getopts("a:dhv", \%switch);
if($switch{a})
{
print "Called with switch -a $switch{a}\n";
}
elsif($switch{d})
{
print "Called with switch -d\n";
}
elsif($switch{h})
{
print "Called with switch -h\n";
}
elsif($switch{v})
{
print "Called with switch -v\n";
}
else
{
my $base=`/usr/bin/basename $0`; chomp $base;
print "ERROR: wrong arguments. Type $base -h for help\n";
}
Possible calls:
myScript
ERROR: wrong arguments. Type myScript -h for help
myScript -h
Called with switch -h
myScript -d
Called with switch -d
myScript -v
Called with switch -v
myScript -a
ERROR: wrong arguments. Type myScript -h for help
myScript -a Hello
Called with switch -a Hello
2.1. Creating array
@array = ("one", "two", "tree");
2.2. Adding value to array
push(@array, "four");
2.3. Getting length of an array
Number of elements:
scalar(@array);
Index of last element:
#@array
Value of an element:
$array[3];
Note that in this case the variable @array is used with the $ symbol and not with the @ symbol. This because only one element is returned from this call.
2.4. Grepping in an array
The following examples list in @match all the lines containing the words stored either in $keyword or @keywords.
my @match = grep { /$keyword/ } @array;
my @match = grep { /@keywords/ } $variable;
my @match = grep { /@keywords/ } @array;
2.5. Sorting an array
my @sorted = sort { $a <=> $b } @input;
Note that this doesn't work:
my @sorted = sort @input;
2.6. Sorting an array with unique elements
Perl doesn't provide such a functionality, therefore you must implement it your self.
Here a working example:
%seen = ();
@array_unique = ();
foreach $item (@array_not_unique)
{
unless($seen{$item})
{
# element not stored yet
$seen{$item} = 1;
push(@array_unique, $item);
}
}
3.1. Code matches
\a Alarm (beep)
\n Newline
\r Carriage return
\t Tab
\f Formfeed
\e Escape
\d A digit, same as [0-9]
\D A nondigit
\w A word character (alphanumeric), same as [a-zA-Z_0-9]
\W A nonword character
\s A whitespace character, same as [ \t\n\r\f]
\S A non-whitespace character
3.2. Assertion meaning
^ Matches at the beginning of the string (or line, if /m used)
$ Matches at the end of the string (or line, if /m used)
\b Matches at word boundary (between \w and \W)
\B Matches except at word boundary
\A Matches at the beginning of the string
\Z Matches at the end of the string
\G Matches where previous m//g left off
(?=...) Matches if engine would match ... next
(?!...) Matches if engine wouldn't match ... next
3.3. Maximal minimal allowed range
{n,m}{n,m}? Must occur at least n times but no more than m times
{n,}{n,}? Must occur at least n times
{n}{n}? Must match exactly n times
**? 0 or more times (same as {0,})
++? 1 or more times (same as {1,})
??? 0 or 1 time (same as {0,1})
4.1. Command grep
The following examples list in @match all the lines containing
the words stored either in $keyword or @keywords.
my @match = grep { /$keyword/ } @array;
my @match = grep { /@keywords/ } $variable;
my @match = grep { /@keywords/ } @array;
5.1. Creating a hash
%hash = ("first index" => "first element",
"second index" => "second element"
);
5.2. Adding value to a hash
$hash{$key} = $value;
5.3. Getting length of a hash
This returns the numbers of keys in the hash (0 = hash is empty):
scalar(keys(%hash));
6.1. Opening file
my $file = "MyFile";
open(FILE, "<$file") or die "ERROR: unable to open $file: $!";
close(FILE);
List of open modes:
Filename Read Write Append Create Trunc O_flags Char
<file yes no no no no RDONLY "r"
>file no yes no yes yes WRONLY TRUNC CREAT "w"
>>file no yes yes yes no WRONLY APPEND CREAT "a"
+<file yes yes no no no RDWR "r+"
+>file yes yes no yes yes RDWR TRUNC CREAT "w+"
+>>file yes yes yes yes no RDWR APPEND CREAT "a+"
open(FH, "filename"); # read from existing file
open(FH, "<filename"); # read from existing file (explicitly)
open(FH, ">filename"); # create file and write to it
open(FH, ">>filename"); # append to existing file
open(FH, "| output-pipe-command"); # set up an output filter
open(FH, "input-pipe-command |"); # set up an input filter
6.2. Reading file line by line
my $file = "MyFile";
open(FILE, "<$file") or die "ERROR: unable to open $file: $!";
while(<FILE>)
{
my $line = $_;
print STDOUT $line;
}
close(FILE);
6.3. Reading a specific line
$. = 0;
do
{
$line = <HANDLE>
}
until $. == $DESIRED_LINE_NUMBER || eof;
or put file content in an array:
@lines = <HANDLE>;
$LINE = $lines[$DESIRED_LINE_NUMBER];
6.4. Reading configuration file
eval `cat $config`;
6.5. Creating temporary file
use IO::File;
$fh = IO::File->new_tmpfile or die "Unable to make new temporary file: $!";
6.6. Renaming a file
rename($old_filename, $new_filename) or die "can't rename $old_filename to $new_filename: $!";
6.7. Deleting a file
unlink($FILENAME) or die "Can't delete $FILENAME: $!\n";
For more files:
unlink(@FILENAMES) == @FILENAMES or die "Couldn't unlink all of @FILENAMES: $!\n";
6.8. Copying a file
use File::Copy;
copy($oldfile, $newfile);
6.9. Locking a file
Call flock() before writing to a file:
open(FILE, "+< $file") or die "can't open $file: $!";
flock(FILE, 2) or die "can't flock $path: $!";
# make something with $file
close(FH)
List of lock modes:
1 Shared lock (for reading)
2 Exclusive lock (for writing)
4 Non-blocking request (don't stall)
8 Free the lock (careful!)
6.10. Getting all files in a directory
opendir(DIR, $dirname) or die "can't opendir $dirname: $!";
while (defined($file = readdir(DIR)))
{
push(@file, "$dirname/$file");
}
closedir(DIR);
6.11. Getting all files in a directory with filename expansions
Get files like a shell would do.
@file = glob("*.txt");
@file = map { glob($_) } "*.c", "*.c,v";
@file = map <${_}>, "*.c", "*.c,v";
6.12. Splitting filename
use File::Basename;
$base = basename($path);
$dir = dirname($path);
($base, $dir, $ext) = fileparse($path);
6.13. Flushing output
If the output doesn't appear immediately, disable buffering:
$old_fh = select(OUTPUT_HANDLE);
$| = 1;
select($old_fh);
or
use IO::Handle;
OUTPUT_HANDLE->autoflush(1);
6.14. Getting file or directory properties
@entry = stat($file) or die "Couldn't stat $file: $!";
List of properties:
Element Abbreviation Description
0 dev Device number of filesystem
1 ino Inode number (the "pointer" field)
2 mode File mode (type and permissions)
3 nlink Number of (hard) links to the file
4 uid Numeric user ID of file's owner
5 gid Numeric group ID of file's owner
6 rdev The device identifier (special files only)
7 size Total size of file, in bytes
8 atime Last access time, in seconds, since the Epoch
9 mtime Last modify time, in seconds, since the Epoch
10 ctime Inode change time, in seconds, since the Epoch
11 blksize Preferred block size for filesystem I/O
12 blocks Actual number of blocks allocated
Example:
use File::stat;
$file = "/bin/ls";
$inode = stat($file);
$ctime = $inode->ctime;
$size = $inode->size;
6.15. Accessing files and printing output at the same time
Once opened a file, the print command redirect all to the opened file. To redirect some messages to the screen, use the following command:
SELECT STDOUT;
and to redirect to the opened file:
SELECT YOUR_FILE_HANDLER;
A much better possibility is to specify always where to redirect the datas:
print FILEHANDLER "This is written into the file\n";
print STDOUT "This is written to the screen\n";
6.16. Passing file handler to a function
my $file = "myFile.txt";
open(FH, "<$file") or die "ERROR: unable to open $file: $!\n";
myFunction(*FH);
close (FH);
sub myFunction($)
{
local *FH = $_[0];
print FH "Hello\n";
}
7.1. Calling a function reading its name from a variable
$func = (caller[0][3])
8.1. Arithmetic operators
EXAMPLE NAME RESULT
$a + $b Addition Sum of $a and $b
$a * $b Multiplication Product of $a and $b
$a % $b Modulus Remainder of $a divided by $b
$a ** $b Exponentiation $a to the power of $b
8.2. Comparison operators
COMPARISON NUMERIC STRING RETURN VALUE
Equal == eq True if $a is equal to $b
Not equal != ne True if $a is not equal to $b
Less than < lt True if $a is less than $b
Greater than > gt True if $a is greater than $b
Less than or equal <= le True if $a not greater than $b
Comparison <=> cmp 0 if equal, 1 if $a greater, -1 if $b greater
8.3. File test operators
EXAMPLE NAME RESULT
-e $a Exists True if file named in $a exists
-r $a Readable True if file named in $a is readable
-w $a Writable True if file named in $a is writable
-d $a Directory True if file named in $a is a directory
-f $a File True if file named in $a is a regular file
-T $a Text File True if file named in $a is a text file
8.4. Logical operators
EXAMPLE NAME RESULT
$a && $b and $a if $a is false, $b otherwise
$a and $b and $a if $a is false, $b otherwise
$a || $b or $a if $a is true, $b otherwise
$a or $b or $a if $a is true, $b otherwise
! $a not True if $a is not true
not $a not True if $a is not true
8.5. String operators
$a = 1;
$b = 2;
print $a + $b; # prints 3
print $a . $b; # prints 12
print $a x $b; # prints 11 (2 times the "1")
All the following exmaples give the same result:
print $a . ' is equal to ' . $b . "\n"; # dot operator
print $a, ' is equal to ', $b, "\n"; # list
print "$a is equal to $b\n"; # interpolation
9.1. Assertions
ASSERTION MEANING
^ Matches at the beginning of the string (or line, if /m used)
$ Matches at the end of the string (or line, if /m used)
\b Matches at word boundary (between \w and \W)
\B Matches except at word boundary
\A Matches at the beginning of the string
\Z Matches at the end of the string
\G Matches where previous m//g left off
(?=...) Matches if engine would match ... next
(?!...) Matches if engine wouldn't match ... next
9.2. Modifiers
MODIFIER MEANING
g Match globally, i.e., find all occurrences
i Do case-insensitive pattern matching
m Treat string as multiple lines
o Only compile pattern once
s Treat string as single line
x Extend your pattern's legibility with whitespace and comments
Example:
m/Hello/i
9.3. Special characters
CODE MATCHES
\a Alarm (beep)
\n Newline
\r Carriage return
\t Tab
\f Formfeed
\e Escape
\d A digit, same as [0-9]
\D A nondigit
\w A word character (alphanumeric), same as [a-zA-Z_0-9]
\W A nonword character
\s A whitespace character, same as [ \t\n\r\f]
\S A non-whitespace character
9.4. Quantifiers
MAXIMAL MINIMAL ALLOWED RANGE
{n,m} {n,m}? Must occur at least n times but no more than m times
{n,} {n,}? Must occur at least n times
{n} {n}? Must match exactly n times
* *? 0 or more times (same as {0,})
+ +? 1 or more times (same as {1,})
? ?? 0 or 1 time (same as {0,1})
10.1. Reading from a program
my $program = "ls -al";
$pid = open(PH, "$program |" or die "ERROR: unable to open $program: $!\n";
while(<PH>)
{
print STDOUT $_;
}
close(PH);
10.2. Writing to a program
my $program = "echo -n";
$pid = open(PH, "| $program" or die "ERROR: unable to open $program: $!\n";
print PH "hello\n";
close(PH);
11.1. Accessing substring
$value = substr($string, $offset, $count);
$value = substr($string, $offset);
To extract the last character(s):
$last = substr($string, -1);
$piece = substr($string, -8, 3);
11.2. Accessing colomns
Forward 6, grab 2, backward 5, grab 2
($b, $c) = unpack("x6 A2 X5 A2", $a);
11.3. Accessing one character at time
@array = split(//, $string);
foreach my $c(@array)
{
# make something with $c
}
11.4. Comparing strings
Strings must be exactly the same:
if($date eq "2004-01-01")
{
print "Today is a new year!\n";
}
String A must contain string B:
if($stringA =~ /$stringB/)
{
}
11.5. Converting TABS to spaces and viceversa
Possibility 1:
while ($string =~ s/\t+/' ' x (length($&) * 8 - length($`) % 8)/e)
{
# spin in empty loop until substitution finally fails
}
Possibility 2:
use Text::Tabs;
$tabstop = 8; # number of spaces
@expanded_lines = expand(@lines_with_tabs);
@tabulated_lines = unexpand(@lines_without_tabs);
11.6. Controlling case
Convert to uppercase:
uc($string);
$string = "\Uabc";
ucfirst =^ \u (???)
Convert to lowercase:
lc($string);
$string = "\LABC";
lcfirst =^ \l (???)
12.1. Swapping variables
$a = "alpha";
$b = "omega";
($a, $b) = ($b, $a);
12.2. Converting ascii to integer and viceversa
$num = ord($char);
$char = chr($num);
$char = sprintf("%c", $num);
printf("Number %d is character %c\n", $num, $num);
12.3. Simple if
$ok ? "STDOUT" : "STDERR";
12.4. Simple repeat character
$separator = "-" x 80;
12.5. Replacing characters and copy the result in a new variable
($a = $b) =~ s/xxx//;
Same as
$a = $b; $a =~ s/xxx//;
12.6. Working with directories
chdir
updir
curdir
12.7. Environment variables
This should return /home/username
$ENV{HOME}
12.8. Getting the script directory
use FindBin qw($Bin);
my $SCRIPT_PATH = $Bin;
12.9. Executing shell script
12.9.1. Using apostrophe
The first possibility is:
`mkdir /test/`
12.9.2. Using "System" call
The second possibility is:
!system("mkdir /test") or die "ERROR: unable to create /test\n";
Note the \n at the end of the line. This will not print at what line the script has been stopped.
Instead, in this case
!system("mkdir /test") or die "ERROR: unable to create /test. Aborting ";
the error message will be
ERROR: unable to create /test. Aborting at line bla bla bla.
12.9.3. Using pipe
Use open with a pipe like:
open(HANDLER, "your system command here |");
while(<HANDLER>)
close HANDLER;
The following example prints all the files present in /tmp having "txt" as extension:
open (HANDLER, "find /tmp -name \"*.txt\" |");
while (<HANDLER>)
{
print $_;
}
close HANDLER;
|
