jusuchin85 · jusuchin85 · Oct 20, 2024 · Nov 21, 2022 · Nov 21, 2022 · Nov 21, 2022
diff --git a/README.md b/README.md
@@ -1 +1,7 @@
-# learnings
+# Learnings
+
+Contains a collection of READMEs for the various areas of my learning. Some of the exercises are from various paid sources, so please support the author of those exercises if possible! 🍺
+
+## Table of Contents
+
+- [GNU `grep` and `ripgrep`](gnu-grep/)
diff --git a/gnu-grep/README.md b/gnu-grep/README.md
@@ -0,0 +1,66 @@
+# GNU grep
+
+Learnings from [GNU GREP and RIPGREP](https://learnbyexample.gumroad.com/l/gnugrep_ripgrep?layout=profile) by [Sundeep Agarwal](https://learnbyexample.gumroad.com/)'
+
+> Ensure that the version of `grep` you're using is 3.7 and above (the default that comes with MacOS is 2.6):
+>
+> ```bash
+> grep --version
+> 
+> grep (GNU grep) 3.8
+> Packaged by Homebrew
+> Copyright (C) 2022 Free Software Foundation, Inc.
+> License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
+> This is free software: you are free to change and redistribute it.
+> There is NO WARRANTY, to the extent permitted by law.
+> 
+> Written by Mike Haertel and others; see
+> <https://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.
+> ```
+>
+> You can install this (as well as others using [Homebrew](gnu-essentials-mac.md))
+## Exercises
+
+- [Chapter 2](exercises/chapter_2/README.md)
+
+## Simple commands
+
+> Example file: [`programming_quotes.txt`](https://github.com/learnbyexample/learn_gnugrep_ripgrep/blob/master/example_files/freq_options/programming_quotes.txt)
+
+| Criteria                                           |                      `grep` Command                      |                             Manual Reference                            |
+|----------------------------------------------------|:--------------------------------------------------------:|:-----------------------------------------------------------------------:|
+| Find a word from a text file                       | `grep '[keyword]' [file]`                                | [Link](https://www.gnu.org/software/grep/manual/grep.html)              |
+| Regex pattern matching                             | `grep -F '[regex_pattern]' [file]`                       | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dF) |
+| Case-insensitive searching                         | `grep -i '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002di) |
+| Inverse matching (ignore lines)                    | `grep -v '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dv) |
+| Line number                                        | `grep -n '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dn) |
+| Line count                                         | `grep -c '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dc) |
+| Limit output lines                                 | `grep -m[lines] '[keyword]' [file]`                      | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dm) |
+| Search multiple strings                            | `grep -e '[first_keyword]' -e '[second_keyword]' [file]` | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002de) |
+| Search multiple strings (keywords from a file)     | `grep -f [keyword_file] [file]`                          | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002df) |
+| List files matching the pattern                    | `grep -l '[keyword]' [file1] [file2]`                    | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dl) |
+| List files NOT matching the pattern                | `grep -L '[keyword]' [file1] [file2]`                    | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dL) |
+| Suppress filename output (default for single file) | `grep -h '[keyword]' [file1] [file2]`                    | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dh) |
+| Show filename output (default for multiple files)  | `grep -H '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dH) |
+| Match whole word only                              | `grep -w '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dw) |
+| Output exact match                                 | `grep -x '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dx) |
+| Common lines between two files                     | `grep -Fxf [file1] [file2]`                              |                                                                         |
+| Extract only matching pattern                      | `grep -o '[keyword]' [file]`                             | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002do) |
+
+## Basic Regular Expression (BRE) / Extended Regular Expression (ERE) Regular Expressions
+
+> Example files: [`word_anchors.txt` and `words.txt`](https://github.com/learnbyexample/learn_gnugrep_ripgrep/tree/master/example_files/bre_ere)
+
+Typical commands:
+
+| Options | Description                                                                                                                                          |                             Manual Reference                            |
+|:-------:|------------------------------------------------------------------------------------------------------------------------------------------------------|:-----------------------------------------------------------------------:|
+|   `-G`  | can be used to specify explicitly that BRE is needed                                                                                                 | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dG) |
+|   `-E`  | will enable Extended Regular Expression (ERE). In GNU `grep`, BRE and ERE only differ in how metacharacters are specified, no difference in features | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dE) |
+|   `-F`  | will cause the search patterns to be treated literally                                                                                               | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dF) |
+|   `-P`  | will enable Perl Compatible Regular Expression (PCRE) (if available)                                                                                 | [Link](https://www.gnu.org/software/grep/manual/grep.html#index-_002dP) |
+
+### Line Anchors
+
+- `^` — start of line
+- `$` — end of line
diff --git a/gnu-grep/exercises/chapter_2/README.md b/gnu-grep/exercises/chapter_2/README.md
@@ -0,0 +1,127 @@
+Format for the exercise is:
+
+- use the [`dracula.txt`](dracula.txt) file as input
+- output is shown for every question within code blocks
+- answer is in code blocks
+
+1. Display all lines containing `ablaze`:
+
+    ```text
+    the room, his face all ablaze with excitement. He rushed up to me and
+    ```
+
+    ```bash
+    grep 'ablaze' dracula.txt
+    ```
+
+1. Display all lines containing `abandon` as a whole word:
+
+    ```text
+    inheritors, being remote, would not be likely to abandon their just
+    ```
+
+    ```bash
+    grep -w 'abandon' dracula.txt
+    ```
+
+1. Display all lines that satisfies both of these conditions:
+
+    - `professor` matched irrespective of case
+    - either `quip` or `sleep` matched case sensitively
+
+    ```text
+    equipment of a professor of the healing craft. When we were shown in,
+    its potency; and she fell into a deep sleep. When the Professor was
+    sleeping, and the Professor seemingly had not moved from his seat at her
+    to sleep, and something weaker when she woke from it. The Professor and
+    ```
+
+    ```bash
+    grep -i 'professor' dracula.txt | grep -e 'quip' -e 'sleep'
+    ```
+
+1. Display first three lines containing `Count`:
+
+    ```text
+    town named by Count Dracula, is a fairly well-known place. I shall enter
+    must ask the Count all about them.)
+    Count Dracula had directed me to go to the Golden Krone Hotel, which I
+    ```
+
+    ```bash
+    grep -m3 'Count' dracula.txt
+    ```
+
+1. Display first six lines containing `Harker` but not either of `Journal` or `Letter`:
+
+    ```text
+    said, "The Herr Englishman?" "Yes," I said, "Jonathan Harker." She
+    "I am Dracula; and I bid you welcome, Mr. Harker, to my house. Come in;
+    I shall be all alone, and my friend Harker Jonathan--nay, pardon me, I
+    Jonathan Harker will not be by my side to correct and aid me. He will be
+    "I write by desire of Mr. Jonathan Harker, who is himself not strong
+    junior partner of the important firm Hawkins & Harker; and so, as you
+    ```
+
+    ```bash
+    grep -v -e 'Journal' -e 'Letter' dracula.txt | grep -m6 'Harker'
+    ```
+
+1. Display lines containing `Zooelogical Gardens` along with line number prefix:
+
+    ```text
+    5597: _Interview with the Keeper in the Zooelogical Gardens._
+    5601:the keeper of the section of the Zooelogical Gardens in which the wolf
+    8042:the Zooelogical Gardens a young one may have got loose, or one be bred
+    ```
+
+    ```bash
+    grep -n 'Zooelogical Gardens' dracula.txt
+    ```
+
+1.  Find total count of whole word `the` (irrespective of case):
+
+    ```text
+    8090
+    ```
+
+    ```bash
+    grep -iow 'the' dracula.txt | wc -l
+    ```
+
+1. The below code snippet tries to get number of empty lines, but apparently shows wrong result, why?
+
+    ```bash
+    $ grep -cx '' dracula.txt
+    0
+    ```
+
+    `dracula.txt` is not a Unix-style file format:
+
+    ```bash
+    file dracula.txt
+
+    dracula.txt: ASCII text, with CRLF line terminators
+    ```
+
+    This can be further reviewed using the `od` command ([manual](https://man7.org/linux/man-pages/man1/od.1.html)):
+
+    ```bash
+    od -c dracula.txt | head -n5
+
+    0000000    T   h   e       P   r   o   j   e   c   t       G   u   t   e
+    0000020    n   b   e   r   g       E   B   o   o   k       o   f       D
+    0000040    r   a   c   u   l   a   ,       b   y       B   r   a   m    
+    0000060    S   t   o   k   e   r  \r  \n  \r  \n   T   h   i   s       e
+    0000100    B   o   o   k       i   s       f   o   r       t   h   e    
+    ```
+
+    This normally means there aren't any empty lines as there are (at least) a `\r` character in every other line other than the new line.
+
+    In order to resolve this, add the `$'\r'` to the `grep` command:
+
+    ```bash
+    grep -cx $'\r' dracula.txt
+
+    2559
+    ```