If you have a very large file on your computer which cannot be easily opened with conventional software - or you want to check a number of files, the head command (in Terminal) can be a quicker way of doing this. For the alternative in Windows' PowerShell (Get-Content), see this guide.
head will show you the first 10 lines of any specified file or files - but you can also specify a different number. A typical command looks like this:
head myfile.csv
The file 'myfile.csv' must be in the same directory as you are when you write the command (to find out what directory you are in, and move, see the instructions here). Or you can specify a path like so:
head somefolder/myfile.csv
You can show the first lines of multiple files by listing them all like so:
head myfile1.csv myfile2.csv
And if they are all the same type, you can use an asterisk wildcard instead like so:
head *.csv
If you are doing this, it's a good idea to create a specific folder just for this task, and put all your files in there.
Another option is to use the results of the ls command (which lists all the files in the current directory) as the basis for head, like so:
ls | head
This is basically a way of saying 'Show me the first line of all files in this directory'.
10 lines is just the default. You can specify a different number of lines using -n followed by the number of lines you want, like so:
head -n1 myfile.csv
This returns the first line (1 line) in that file - with a spreadsheet, this is a useful way of just seeing the headings.
You can actually write this in a number of ways, with a space:
head -n 1 myfile.csv
Or without n at all:
head -1 myfile.csv
Until now these commands have only printed (displayed) the results in the place where you are typing command line. But you will probably want to store them in a new file to study or analyse them further. To do that add the > command follwed by the name of the new file that you want to create, like so:
head -n1 myfile.csv > myheaders.csv
This new file will be created in the same directory as you have been writing this code.
You can read more about the head command in the documentation here. This includes how to grab the first number of characters using -c, how to sort the results, and the alternative tail command