The first topic that I’ve chosen to export it from my mind is Regex. While Regex is handy and you can pick it up quickly, it causes tons of frustration. You can use it everywhere when you want to search for a specific part of your file, no matter if it’s a Sublime Text Editor or a grep command in Linux.
In this article, I show some basic examples of Regex with grep in a Linux Terminal. For those who may not know what’s grep for: grep is a single command in Linux for searching a text data with a specific patterns and it uses as following:
grep [options] PATTERN [file]
If you want to know available options of grep, you can easily go through the grep –help (in Ubuntu) since it contains all options that you have for using this command. Anyway, let’s go back to the topic:
We use Regext for finding the pattern that we want. However, Regex uses special expressions in combination with any of the following:
Literal
Any character used in a search or matching expression
Metachracter
One or more special characters with special meaning
Escape Sequence
Use of metachracters as a literal
Most difficult part of using Regex is how to build a pattern for finding what we want! Following are some basic options of Regex:
[ ] Matches anything inside brackets. It can be either number or letters but.
Be aware that, it's case sensitive.
- This option creates a range. For example, 1-9 means between 1 to 9 OR a-z means between a to z.
Be aware that, it's case sensitive and you shouldn't use space between.
. Find any character in its position.
* Matches any character zero or more times
^ Negates a search when used inside brackets.
The caret is used outside brackets to find only lines that begin with a given string.
( ) Combine multiple patterns.
| Find left or right values. Mostly used with () option.
$ Find line base on their ending character. It's Similar to caret outside brackets.
Well, we’re the generation of UI so it’s mind blowing to go through all of them without any example. Let’s assume that we have following text file:
Here is my sample text file
This text file contains 10 lines
Let's search for my name "saleh"
Love my wife
love my life
I born in 1987
November is the best month
1987 + 11 + 18 = 2016
WoW, my birthday equation is the year that I posted this!
Now we want to find:
All lines that start with either L or l
saleh@Saleh:~/Personal Project$ grep ^[Ll]. saleh.txt
Result:
Let's search for my name "saleh"
Love my wife
love my life
Find saleh:
saleh@Saleh:~/Personal Project$ grep saleh saleh.txt
Result:
Let's search for my name "saleh"
Find all Lines start with L
saleh@Saleh:~/Personal Project$ grep ^L saleh.txt
Result:
Let's search for my name "saleh"
Love my wife
Hope she visits this site and see this
Find Numbers Only
saleh@Saleh:~/Personal Project$ grep -v [A-Za-z] saleh.txt
Result:
1987 + 11 + 18 = 2016
-v prints non-matching lines and it’s one of the grep options
Find any lines that has number
saleh@Saleh:~/Personal Project$ grep [0-9] saleh.txt
Result:
This text file contains 10 lines
I born on 1987
1987 + 11 + 18 = 2016
You can always use the combination of above for building your search patterns. However, don’t forget that prior to going through the patterns you need to know what you want to find. Hope it helps.
