Extraction of strings and lines in a file
●Extract strings that start with a specific character
If you want to extract a specific string from a long file, use the grep command.
By specifying the string to be extracted and the file as the arguments of the grep command, and by adding "^" (carrot) as an additional condition to extract data starting from a specific string, you can extract data starting from that string.
| [root@Lion ~]# grep -i "ja" country_list.txt ↑Option "-i" to extract strings containing "ja" in a case-insensitive manner Japan Azerbaijan Jamaica Libyan Arab Jamahiriya ↑Multiple string data containing "ja" will be extracted. [root@Lion ~]# grep -i "^ja" country_list.txt ↑Use option "-i" to extract strings starting with "ja" in a case-insensitive manner Japan Jamaica ↑The string data starting with "ja" will be extracted. |
●Extract strings ending with a specific character
In order to extract data ending with a specific string, "$" (Dollar) can be added.
| [root@Lion ~]# grep -i "en" country_list.txt ↑The option "-i" extracts strings containing "en" in a case-insensitive manner Argentina Armenia Benin Central African Republic Denmark Grenada Kenya Liechtenstein Montenegro Saint Vincent and the Grenadines Senegal Slovenia Sweden Turkmenistan Venezuela Yemen ↑Multiple string data containing "en" will be extracted. [root@Lion ~]# grep -i "en$" country_list.txt ↑Use the option "-i" to extract strings ending in "en" in a case-insensitive manner Sweden Yemen ↑String data ending with "en" will be extracted. |
●Display a specific string including line numbers.
You can use the grep command to search for and extract a specific string in a file.
However, it does not tell you in which line of the file the string is located.
If you want to extract the search string along with the line number, run the grep command with the option "-n".
| [root@Lion ~]# grep -in "en" country_list.txt ←Displays a string with line numbers. 7:Argentina 8:Armenia 19:Benin 33:Central African Republic 49:Denmark 70:Grenada 90:Kenya 100:Liechtenstein 116:Montenegro 148:Saint Vincent and the Grenadines 153:Senegal 159:Slovenia 168:Sweden 180:Turkmenistan 191:Venezuela 193:Yemen ↑A string containing "en" will be displayed with the line number. |
●Extract lines that do not contain a specific string.
To exclude specific strings from the file and display them, run the grep command with the "-v" option
| [root@Lion ~]# more country_list.txt Japan Afghanistan Algeria Andorra Angola Antigua and Barbuda Argentina Armenia Australia Austria[root@Lion ~]# grep -iv "an" country_list.txt ←Display lines containing "an" without it. Algeria Argentina Armenia Australia Austria Bahamas Bahrain Barbados Belarus Belgium Belize Benin ↑ The results will be displayed without the line containing "an". |
●Displays the number of lines that contain a specific string.
By using the "-c" option to the grep command, the number of lines containing a specific string will be displayed
| [root@Lion ~]# grep -i "en" country_list.txt ←Show lines containing "en Argentina Armenia Benin Central African Republic Denmark Grenada Kenya Liechtenstein Montenegro Saint Vincent and the Grenadines Senegal Slovenia Sweden Turkmenistan Venezuela YemenDisplay the number of lines containing "en [root@Lion ~]# grep -ic "en" country_list.txt ←Display the number of lines that contain en 16 ←There are 16 lines. |