working on traefik integration

content/AWK cheatsheet.md

@@ -0,0 +1,171 @@
+---
+tags:
+  - AI
+  - notes
+  - coding-notes
+  - docs
+  - public
+---
+### 1. Basic Syntax
+
+The standard structure of an `awk` command:
+
+Bash
+
+```
+awk [options] 'BEGIN { initialization } pattern { action } END { finalization }' file
+```
+commands
+- **`BEGIN { ... }`**: Runs _once_ before the first line is read. Great for setting variables or printing headers.
+    
+- **`pattern`**: A condition (regex or math) that must be met for the action to run.
+    
+- **`{ action }`**: The command(s) executed on each line that matches the pattern.
+    
+- **`END { ... }`**: Runs _once_ after the last line is processed. Great for printing totals or summaries.
+    
+
+---
+
+### 2. Common Command-Line Flags
+
+|**Flag**|**Description**|**Example**|
+|---|---|---|
+|`-F`|Defines the field separator (default is space/tab)|`awk -F"," '{print $1}' file.csv`|
+|`-v`|Assigns an external variable to use inside AWK|`awk -v max=100 '$1 > max' file`|
+|`-f`|Reads AWK commands from a script file|`awk -f script.awk input.txt`|
+|`-i inplace`|Edits the file in place (requires GNU awk)|`gawk -i inplace '{print $1}' file`|
+
+---
+
+### 3. Built-in Variables
+
+|**Variable**|**Meaning**|**Example Use Case**|
+|---|---|---|
+|`$0`|The entire current line|`print $0`|
+|`$1, $n`|The 1st, 2nd... _n_th field (column)|`print $2, $4`|
+|`NR`|Number of Records (Current line number)|`NR > 1` (Skip headers)|
+|`NF`|Number of Fields (Total columns in current line)|`print $NF` (Print the last column)|
+|`FS`|Input Field Separator (Same as `-F`)|`BEGIN { FS=":" }`|
+|`OFS`|Output Field Separator|`BEGIN { OFS="," }`|
+|`RS`|Input Record Separator (Default: newline)|`BEGIN { RS="" }` (Paragraph mode)|
+|`ORS`|Output Record Separator (Default: newline)|`BEGIN { ORS="\n\n" }` (Double space)|
+
+---
+
+### 4. Operators & Conditionals
+
+**Relational & Logical Operators:**
+
+- `==`, `!=`, `<`, `>`, `<=`, `>=` (Standard math comparisons)
+    
+- `~` (Matches regular expression)
+    
+- `!~` (Does not match regular expression)
+    
+- `&&` (AND), `||` (OR), `!` (NOT)
+    
+
+**Control Structures (used inside action blocks):**
+
+```
+# If/Else Statement
+{ if ($1 > 50) print "Pass"; else print "Fail" }
+
+# For Loop
+{ for (i=1; i<=NF; i++) print $i }
+
+# While Loop
+{ i=1; while (i<=NF) { print $i; i++ } }
+```
+
+---
+
+### 5. Essential Built-in Functions
+
+|**Function**|**Description**|**Example**|
+|---|---|---|
+|`length(str)`|Returns the length of a string|`length($0) > 80`|
+|`tolower(str)`|Converts string to lowercase|`print tolower($1)`|
+|`toupper(str)`|Converts string to uppercase|`print toupper($1)`|
+|`substr(s,p,l)`|Extracts substring from _s_ starting at _p_ with length _l_|`print substr($1, 1, 3)`|
+|`gsub(r,s,t)`|Globally replaces regex _r_ with string _s_ in target _t_|`gsub(/apple/, "orange", $0)`|
+
+---
+
+### 6. Handy Everyday One-Liners
+
+**Printing & Filtering:**
+
+- **Print the last column of every line:**
+    
+    Bash
+    
+    ```
+    awk '{ print $NF }' file.txt
+    ```
+    
+- **Print lines longer than 80 characters:**
+    
+    Bash
+    
+    ```
+    awk 'length($0) > 80' file.txt
+    ```
+    
+- **Print lines matching "Error" or "Warning":**
+    
+    Bash
+    
+    ```
+    awk '/Error|Warning/' file.log
+    ```
+    
+
+**Math & Summaries:**
+
+- **Sum the values in the first column:**
+    
+    Bash
+    
+    ```
+    awk '{ sum += $1 } END { print sum }' numbers.txt
+    ```
+    
+- **Calculate the average of the first column:**
+    
+    Bash
+    
+    ```
+    awk '{ sum += $1 } END { print sum / NR }' numbers.txt
+    ```
+    
+- **Count the number of empty lines:**
+    
+    Bash
+    
+    ```
+    awk '/^$/ { count++ } END { print count }' file.txt
+    ```
+    
+
+**Text Manipulation:**
+
+- **Remove duplicate consecutive lines (simulates `uniq`):**
+    
+    Bash
+    
+    ```
+    awk 'a != $0; { a = $0 }' file.txt
+    ```
+    
+- **Number each line (simulates `cat -n`):**
+    
+    Bash
+    
+    ```
+    awk '{ print NR, $0 }' file.txt
+    ```
+    
+
+---