The UNIX School

Perl : Remove duplicate elements from arrays

guru@theunixschool.com — Mon, 13 May 2013 22:18:34 PDT

How to remove duplicate element from arrays in Perl? Let us see in this article how can duplicates be removed in different ways? 1. Copying distinct elements to new array using grep function: my...

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Perl - 6 examples to fetch date / time without Linux date command

guru@theunixschool.com — Wed, 10 Apr 2013 04:01:32 PDT

How to fetch date and time related stuff within in Perl? Sometimes, Perl developers resort to using of Unix system date command to fetch a date or time within Perl script. This is not...

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Perl - How to find the sum of digits in a number?

guru@theunixschool.com — Tue, 26 Mar 2013 03:40:22 PDT

How to find the sum of all the digits in a number or a string? OR How to find the sum of all elements in array? Let us see the different ways how it can be done in Perl? 1. Divide and...

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How to remove leading zeros in a string in Linux?

guru@theunixschool.com — Thu, 14 Mar 2013 03:43:39 PDT

How to remove leading zeros in a variable or a string? Let us consider a variable "x" which has the below value : $ x=0010 $ echo $x 0010 1. Using typeset command of ksh: $ typeset -LZ x $...

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Perl - What is DATA ?

guru@theunixschool.com — Tue, 26 Feb 2013 02:33:00 PST

What is __DATA__ ? Why is it used? Generally, Perl reads data from a file which in the Perl program can be accessed using open and readline functions. However, for users who just want...

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What is the time command in Linux for?

guru@theunixschool.com — Tue, 19 Feb 2013 03:23:57 PST

time command in Unix is used to find the time taken by a particular command to execute. This is very useful when we want to time a particular command or a particular script to know the amount of time...

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sed - 10 examples to replace / delete / print lines of CSV file

guru@theunixschool.com — Tue, 12 Feb 2013 02:55:07 PST

How to use sed to work with a CSV file? Or How to work with any file in which fields are separated by a delimiter? Let us consider a sample CSV file with the following content: cat...

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How to delete every nth line in a file in Linux?

guru@theunixschool.com — Wed, 06 Feb 2013 03:07:31 PST

How to delete or remove every nth line in a file? The requirement is to remove every 3rd line in the file. Let us consider a file with the below content. $ cat...

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Perl - How to split a string into words?

guru@theunixschool.com — Tue, 05 Feb 2013 03:03:38 PST

How to split a string into individual words? Let us see in this article how to split a string which has 2 words separated by spaces. 1. Using the split inbuilt function: my $str="hi...

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gawk - Calculate date / time difference between timestamps

guru@theunixschool.com — Mon, 04 Feb 2013 01:56:15 PST

How to find the time difference between timestamps using gawk? Let us consider a file where the 1st column is the Process name, 2nd...

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gawk - Date and time calculation functions

guru@theunixschool.com — Mon, 21 Jan 2013 01:56:24 PST

gawk has 3 functions to calculate date and time: systime strftime mktime Let us see in this article how to use these functions: systime: This function is equivalent...

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What is UNIX time?

guru@theunixschool.com — Thu, 17 Jan 2013 01:18:45 PST

1. What is Unix Time? Unix time is total number of seconds measured since 01-Jan-1970 00:00:00. This time format is used in all the Unix flavors for time computing activities such...

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Perl - Split a string into individual character array

guru@theunixschool.com — Tue, 15 Jan 2013 06:41:00 PST

How to split a string into individual characters and store in an array in Perl? Let us see in this article how to split a string 'welcome' into separate characters. 1. Using the split...

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Perl - How to print a hash?

guru@theunixschool.com — Wed, 02 Jan 2013 01:33:39 PST

How to print the contents of a hash? Let us see in this article the different options to print a hash. 1. Using foreach and keys: #!/usr/bin/perl use warnings; use strict; $\="\n"; my %h1=(Jan...

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Perl - Return a value from function depending on the context

guru@theunixschool.com — Wed, 19 Dec 2012 00:31:30 PST

How to return a value from a function depending on the context? For example, if the return value is collected into an array, the function should return an array, if collected in a scalar, then...

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Shell Script - How to dump a Oracle table into a CSV file?

guru@theunixschool.com — Mon, 17 Dec 2012 02:32:41 PST

How to dump /export the contents of an Oracle table into a CSV file? Let us write a shell script to dump the content of EMP table into a CSV file. Shell...

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How to print every nth line in a file in Linux?

guru@theunixschool.com — Wed, 12 Dec 2012 02:09:47 PST

How to print every nth line of a file? The requirement is to print every 3rd line of the file. Let us consider a file with the following content. $ cat...

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sed - 10 examples to print lines from a file

guru@theunixschool.com — Tue, 11 Dec 2012 06:44:11 PST

In this article of sed series, we will see how to print a particular line using the print(p) command of sed. Let us consider a file with the following contents: $ cat...

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10 examples of initializing a Hash variable in Perl

guru@theunixschool.com — Wed, 05 Dec 2012 08:08:42 PST

Hash'es is one of the most important concepts in Perl. Hashes are associative arrays where the data is stored in the form of key-value pairs. The big advantage of a hash is faster...

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How to remove the leading and trailing spaces in a file?

guru@theunixschool.com — Mon, 03 Dec 2012 02:04:13 PST

How to remove / delete the leading and trailing spaces in a file? How to replace a group of spaces with a single space? Let us consider a file with the below content: $ cat file ...

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25 examples of vi / vim substitution commands

guru@theunixschool.com — Tue, 27 Nov 2012 22:20:21 PST

In this article, we will see the commonly used vi substitution commands. All the below commands are to be given in escape mode: Common tricks: 1. To replace the 1st occurrence of 'a' with...

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awk - 10 examples to insert / remove / update fields of a CSV file

guru@theunixschool.com — Sun, 25 Nov 2012 23:22:03 PST

How to manipulate a text / CSV file using awk/gawk? How to insert/add a column between columns, remove columns, or to update a particular column? Let us discuss in this article. Consider a CSV...

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7 examples of find command with xargs in Linux

guru@theunixschool.com — Thu, 22 Nov 2012 01:15:15 PST

find command becomes very powerful when used with xargs. xargs is a beautiful command which actually builds a command and executes it. Though xargs command can be used standalone to work on...

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How to swap 2 columns in a file in Linux?

guru@theunixschool.com — Mon, 19 Nov 2012 02:01:24 PST

How to swap 2 columns or fields in a text or a CSV file? Let us consider a file with the following contents. The requirement is to swap the first 2 fields: $ cat...

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How to retrieve or extract the tag value from XML in Linux?

guru@theunixschool.com — Wed, 07 Nov 2012 01:38:21 PST

How to fetch the tag value for a given tag from a simple XML file? Let us consider a simple XML file, cust.xml, with customer details as below: <?xml version="1.0"...

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