Use grep and regular expressions to analyze text

Use grep and regular expressions to analyze text

In Linux/Unix environment, there are several built in tools that uses generally to do file and directory management. One that popular is grep that often combined with Regular Expressons or regex in short. There are other tools as well like sed, awk, even vi (as my favorite text editor) that could be combine with regex. But in this section, lets start with grep.

Given a text file pets.txt contains random numbers next to animal name

[root@1305ce547374 home]# cat pets.txt 
13824 cat
31406 dog
9235 pig
29145 turtle
5094 lizard
3660 snake

Filter lines start with or end with a specific character

To filter any strings start with or end with particular caracter we could use ^ for any lines start with a given character, and $ to filters any line end with a given character, as follow:

[root@1305ce547374 home]# cat pets.txt|grep "^3"
31406 dog
3660 snake
[root@1305ce547374 home]# cat pets.txt|grep "e$"
29145 turtle
3660 snake

Invert the filter result

On the other hand, to filter any lines not started with - for example - 3, we could use v opton on the grep command

[root@1305ce547374 home]# grep -v "^3" pets.txt 
13824 cat
9235 pig
29145 turtle
5094 lizard

Combining filters

We could also combine the filters in two ways as follow

[root@1305ce547374 home]# grep -v "^3" pets.txt |grep -v "e$"
13824 cat
9235 pig
5094 lizard

[root@1305ce547374 home]# grep -v "^3\|e$" pets.txt 
13824 cat
9235 pig
5094 lizard

Filter lines contains characters follow with any specific characters

If I wanted to filter specific strings follows with other specific character, I could use this grep and regex combination

[root@1305ce547374 home]# grep "[35].*i" pets.txt 
9235 pig
5094 lizard

---

20240214-132719 – Will continue to update this page covers topic relatet regex combination with other tools

---

This material is refers to the rhca objectives