Ever thought of having a database as a single TEXT file ? You could do that, but how do you extract data from it ?

This tutorial deals with extracting data from a SINGLE file very much similar to a RDBMS SELECT with WHERE query.

Let's create a file with the following lines -

A;A1;A2;A3;A4;A5
B;B1;B2;B3;B4;B5
C;C1;C2;C3;C4;C5
D;D1;D2;D3;D4;D5
E;E1;E2;E3;E4;E5
F;F1;F2;F3;F4;F5

As you see above, data has been separated by semicolons (;).

Suppose you want to extract the 4th field from the file for the record which starts with C.

To do the above, use this -

$ grep ^C file | cut -f4 -d\;

Please note that this will give you the value which says C3. This is because the first entry itself is a field.

In the above command, grep ^C means show all lines starting with the letter C.

And the next part cut -f4 -d\; means ONLY show the fourth field and since we have separated our fields by a semicolon, the -d\; option is used. Here you need to put the backslash before the semicolon because semicolon is a SHELL character. You could also use colon (:) in the file and the cut command to avoid this problem.

Please comment if you have questions/suggestions.