Linux-Basics-Complete-Course-With-Notes-Slides

Searching for files and Patterns

In this section, we will take a look at how to locate a file or directory in the filesystem.

locate
find
grep

locate

Lets say you want to find the files with the name City.txt. Easiest way to do this is to make use of locate command.

Run locate command followed by the filename you are searching as an argument. This should return all paths matching the pattern.
```
$ locate City.txt
```
The downside of the locate command is it depends on a database called mlocate.db for querying the filename.
If you have just installed linux or if the file you are trying to locate was created recently. The locate command may not give you useful results. This is because it is possible that the DB is not been updated yet.
To manually update the DB, run the command updatedb and then run the locate command again
```
$ sudo updatedb
```
Please note that the updatedb command needs to be run as root user to work.

find

Another way to do this is make use of the find command. Use the find command followed by the directory under which you want to search. To search file by a name use the -name option followed by the name of the file.

$ find /home/michael -name City.txt

locate-find

Grep

To search within files, the most popular command in linux is grep.

Grep is commonly used to print lines of a file matching a pattern but it also offers a variety of other options as well.
The grep command is case-sensitive

To search for the word second from the sample.txt

$ grep second sample.txt

To search for the word capital with case-insensitive use -i flag.

$ grep -i capital sample.txt

To search for a pattern recursively.

$ grep -r "thrid Line" /home/michael

To print the lines that don’t matches the pattern

$ grep -v "printed" sample.txt

grep

What if you want to match a pattern that form a whole word?

To search for the whole word called exam. Use grep followed by -w flag

$ grep -w exam examples.txt

You can also combine multiple options together. For example, to reverse the search and print all lines of the same file that doesn’t match the whole word exam. Use grep -vw

$ grep -vw exam examples.txt

To print the number of lines after and before matching a pattern. Use grep command with -A and -B flags respectively.

$ grep -A1 Arsenal premier-league-table.txt
$ grep -B1 4 premier-league-table.txt

grep1

Finally, the -A and -B can be combined into one single search.

$ grep -A1 -B1 Chelsea premier-league-table.txt

grep2