Here are some regular expressions that will help you to perform a validation and to extract all matched IP addresses from a file. The following regular expressions match IPv4 addresses. Matched IP addresses can be extracted from a file using grep command. In this article you’ll find a regular expressions themselves and an example of […]
text-processing
SED/AWK – Add to the End or Beginning of a Line
From time to time it is required to modify some file very fast. And it goes without saying that the most popular command line tools for this in Linux are sed and awk – the two best text processing programs. In the following article, you’ll find an information about how to add some text, character […]
RegEx: Find Email Addresses in a File using Grep
Here is a best regular expression that will help you to perform a validation and to extract all matched email addresses from a file. This regular expression matches 99% of the email addresses in use nowadays. In this article you’ll find a regular expression itself and an example of how to extract matched email addresses […]
Removing First and Last Characters From Strings in Bash
From the following article, you’ll learn how to remove first characters from the beginning of each line in Bash and how to print strings between first and last characters using cut command. You’ll also learn how to remove last characters of each line using trick with reverse command. I’ve created a file with the following […]
AWK: Print Column – Change Field Separator – Linux Bash
The awk is a powerful Linux command line tool, that can process the input data as columns. In the following note i will show how to print columns by numbers – first, second, last, multiple columns etc. I will show how to change the default field separator in awk. At the end of this article […]
Grep OR – Grep AND – Grep NOT – Match Multiple Patterns
The grep, egrep, sed and awk are the most common Linux command line tools for parsing files. From the following article you’ll learn how to match multiple patterns with the OR, AND, NOT operators, using grep, egrep, sed and awk commands from the Linux command line. I’ll show the examples of how to find the […]
Using SED and AWK to Print Lines Between Two Patterns
From the following article, you’ll learn how to print lines between two patterns in bash. I’ll show how to to extract and print strings between two patterns using sed and awk commands. I’ve created a file with the following text. It’ll be used in the examples below, to print text between strings with patterns. I […]
HowTo: View a Config File Without Comments
With the help of ‘grep’ command it is quite easy just to look at the active setting of configuration files, omitting comments. The following command will display the content of the file ‘somefile.conf’, omitting blank lines and the lines started with “#”: $ grep ^[^#] somefile.conf Also, you can pipe the output to a new […]
HowTo: Remove Blank Lines From a File
Use one of the following commands to remove blank lines from a file. 1. Using the grep command: $ grep -v “^$” file.txt 2. Using the sed command: $ sed ‘/^$/d’ file.txt 3. Using the awk command: $ awk ‘/./’ file.txt 4. Using the tr command: $ tr -s ‘\n’ < file.txt You also can […]