Text Processing

To count the number of lines in a file, use wc -l:

        $ wc -l dogs.txt
        
      

This is very useful when combined with other commands. For example, you can combine it with grep to count the number of lines matching a specific pattern:

        $ grep 'teddy' dogs.txt | wc -l
        
      

Another thing you can do is to count directory entries with ls | wc -l.

Sorting output can be done with the sort command:

        $ sort dogs.txt
        
      

To sort numbers, use the -n flag:

        $ sort -n numbers.txt
        
      

You can always use -r to reverse the order of the sorting.

It's also possible to sort human-readable values like GB, MB, etc with -h:

        $ du -h . | sort -h
        
      

You can learn more about the du command in the disk space guide.

cut is used to extract specific columns from each line in a file. It is almost always used in combination with the -d and -f flags. -d specifies the delimiter to use to split a line into columns and -f specifies the columns to extract.

This is very useful if you're working with structured data. For example, if you have a CSV (Comma-Separated Values) file:

        $ cut -d ',' -f 2 dogs.csv
        
      

The -f flag also supports ranges of columns:

        $ cut -d ',' -f 2- dogs.csv
        
      

        $ cut -d ',' -f -3 dogs.csv
        
      

        $ cut -d ',' -f 2-4 dogs.csv