StackGrep

StackGrep - An advanced custom grep engine.

How it works?

StackGrep is a Haskell program that receives a file as the only parameter on the command line. The program should display all the lines in that file and prompt the user which string to filter. The program filters the file and shows only the lines that contain the filtered strings. pop is special string that removes a filter from the filtered string stack. The program terminates when introduced a pop string, and when there are no filters in the stack.

Example

Take for example the example-file.txt file provided in the repository.

The file has the following content:

[haskell] Data.List
[haskell] System.Environment
[java] java.util.List
[java] java.util.ArrayList
[java] java.io.File

Run StackGrep with provided file example-file.txt:

$ runhaskell StackGrep.hs example-file.txt

[haskell] Data.List
[haskell] System.Environment
[java] java.util.List
[java] java.util.ArrayList
[java] java.io.File

Filtering:
> _

At this point, the program must accept any string as input. If this string is different from "pop" (this string has a special role, explained below), we will repeat the process, showing only the lines of the file containing the string

Filtering:
> java

[java] java.util.List
[java] java.util.ArrayList
[java] java.io.File

Filtering: java
> _

We can now repeat the process, filtering this time for example by the string util:

> util
[java] java.util.List
[java] java.util.ArrayList
Filtering: java, util

Filtering: java, util
> _

This time we're going to insert the special "pop" command. By doing so, the program will remove the last filter applied:

Filtering: java, util
> pop
[java] java.util.List
[java] java.util.ArrayList
[java] java.io.File

Filtering: java
> _

Now we can add a filter again, or undo (unstack) the last filter. We opted for the second option.

Filtering: java
> pop
[haskell] Data.List
[haskell] System.Environment
[java] java.util.List
[java] java.util.ArrayList
[java] java.io.File

Filtering:
> _

One last "pop" terminates the program.

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Requirements:

• Haskell installed

Install here: https://www.haskell.org/

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Usage:

Compile

ghc --make StackGrep

Run

./StackGrep

Compile and run once

runhaskell StackGrep.hs example-file.txt