molecularsciences.org

The following code read the contents of a text file

#!/bin/bash
filename='links.txt'
while read -r line
do
    echo $line
done <"$filename"

To read first five lines only

head -5 dinks.txt | while read a; do
    echo $a;
done

Read five lines and then delete those lines

head -5 links.txt | while read a; do
    echo $a;
done
sed -i "1,5 d" links.txt

Following code uses DOM to extract links.

Perl string literals are enclosed in quotation marks. You can use either single quotes ('') or double quotes ("").

print "hello";
print 'hello'; 

Now suppose you need to print a string which contains a single or double quote such as following strings:

This is bob's watch.
Alice replied, "It was a birthday gift."

If I do the following,

Problem

You pushed your changes to GIT but you don't see it in the repository.

Diagnosis

First thing is to compare status with log

git log

will give you a list of the commits. You will not see your changes here.

git status

You will see your files here. Above the list of files, you will see

Changes to be committed

Cause

The reason you don't see your changes in repository is because they were not committed.

If a string contains a single quote, it will generate an error. mysqli->real_escape_string() escapes quotes for MySQL. See example:

Replace multiple spaces with one space

See the following code:

<?php
  $str = 'This    string    has   many   spaces';
  $str = preg_replace('/\s+/', ' ', $str);
  print $str;
?>

output

This string has many spaces

Epoch time is Unix timestamp which counts the number of seconds since January 1 1970 00:00:00 UTC. Without getting into long discussion, follow is how your convert between human readable date and epoch time.

Convert Human Readable Date to Epoch Time

<?php
  $now = strtotime('2010-04-25');
  print $now;
?>

Convert Epoch Time to Human Readable Time

Validating email is more difficult than one might think. Recently I found this this code at PHP.net and I feel a need to republish this to emphasize its effectiveness and simplicity.

Passing arrays by value and reference

The difference between passing by value and passing by reference is that you when pass by value, you are passing a copy of the array. When passing by reference, you are passing a pointer i.e any changes made in the function you pass to can modify the original.

function foo($var) {
  $var[1]++;
}
function bar(&$var) {
  $var[1]++;
}

$a=array(5,6,7);
foo($a);
print "Passed by value:\n";
print_r($a);
bar($a);
print "Passed by reference:\n";
print_r($a);

output

Opening directory and listing files

See the following code:

<?php
  $dir = 'mydir';
  $myfiles = scandir($dir);
  print_r($myfiles);
?>

output:

Array
(
  [0] => .
  [1] => ..
  [2] => one.txt
  [3] => two.txt
)

To remove certain file name from the list, see the following code: