updated README

README.md

@@ -46,11 +46,28 @@ Use the `{<group_index>}` syntax to use a specific capturing group.
 - `{2}` matches the second capturing group
 - and so on
 
+#### Coloring
+
+Coloring a reference to a capturing group can be done via `{1:<color>}`.
+
+`<color>` can be one of the following values:
+
+- `black`
+- `red`
+- `green`
+- `yellow`
+- `blue`
+- `magenta`
+- `cyan`
+- `white`
+
+Leaving the color argument empty results into the default color.
+
 #### Formatting
 
-When referencing capturing groups, you can add a specific format for some data types as well using a simplified printf syntax.
+When referencing capturing groups, you can add a specific format for some data types using a simplified printf syntax.
 
-You can use them using this syntax: `{1:%d}`. It will parse the first capturing group into an integer to get rid of leading zeros. Additionally, you can provide a given amount of leading zeros via: `{1:%03d}` for a total length of 3 digits.
+You can use them using this syntax: `{1::%d}`. It will parse the first capturing group into an integer to get rid of leading zeros. Additionally, you can provide a given amount of leading zeros via: `{1::%03d}` for a total length of 3 digits.
 
 The same method can also be applied to `%f` to further format floating point values.
 See a full list of formatting options at [Go's fmt spec](https://pkg.go.dev/fmt).
@@ -61,7 +78,7 @@ Currently only `%s`, `%d`, `%f` and `%g` are supported though.
 
 Mutators are a simple way of manipulating number values like integers and floats using a simple math-like expression
 
-You can provide a mutator using the syntax: `{1:%d:+1}`. It will parse the first capturing group into an integer, adds 1 and then formats the result using the printf format `%d`.
+You can provide a mutator using the syntax: `{1::%d:+1}`. It will parse the first capturing group into an integer, adds 1 and then formats the result using the printf format `%d`.
 
 A mutator always consists of an operator and a value. In the example above `+` is the operator and `1` is the value.
 
@@ -71,11 +88,11 @@ The following operators are supported for `%d`, `%f` and `%g` formats:
 - `*`
 - `/`
 
-It is possible to add multiple mutators by just concatenating them: `{1:%d:*2+1}`.
+It is possible to add multiple mutators by just concatenating them: `{1::%d:*2+1}`.
 
 **Multiple mutators will not follow any order of operations. They are simply applied from left to right!**
 
-Furthermore you can reference caputring groups which will be parsed as the same type to apply its value. This is done via the following syntax: `{1:%d:+(2)}`. It will parse the first and second capturing group into integers and adds them.
+Furthermore you can reference caputring groups which will be parsed as the same type to apply its value. This is done via the following syntax: `{1::%d:+(2)}`. It will parse the first and second capturing group into integers and adds them.
 
 ### Handling unmatched lines
 
@@ -153,7 +170,7 @@ Input:
 
 Command:
 ```sh
-format -i '\d+' -o '{0:%d}'
+format -i '\d+' -o '{0::%d}'
 ```
 
 Output:
@@ -175,7 +192,7 @@ Input:
 
 Command:
 ```sh
-format -i '(\d{4})-(\d{2})-(\d{2})' -o 'day: {3:%d} | month: {2:%d} | year: {1}'
+format -i '(\d{4})-(\d{2})-(\d{2})' -o 'day: {3::%d} | month: {2::%d} | year: {1}'
 ```
 
 Output:
@@ -198,8 +215,8 @@ Input:
 
 Command:
 ```sh
-format -i '(\d{4})-(\d{2})-(\d{2})' -o 'day: {3:%d} | month: {2:%d} | year: {1}' -k |
-format -i '(\d{2})\.(\d{2})\.(\d{4})' -o 'day: {1:%d} | month: {2:%d} | year: {3}' -k
+format -i '(\d{4})-(\d{2})-(\d{2})' -o 'day: {3::%d} | month: {2::%d} | year: {1}' -k |
+format -i '(\d{2})\.(\d{2})\.(\d{4})' -o 'day: {1::%d} | month: {2::%d} | year: {3}' -k
 ```
 
 Output:
@@ -231,7 +248,7 @@ day: 02
 
 Command:
 ```sh
-format -n 3 -i '^year: (\d{4})\nmonth: (\d{2})\nday: (\d{2})$' -o 'day: {3:%d} | month: {2:%d} | year: {1}'
+format -n 3 -i '^year: (\d{4})\nmonth: (\d{2})\nday: (\d{2})$' -o 'day: {3::%d} | month: {2::%d} | year: {1}'
 ```
 
 Output:
@@ -255,7 +272,7 @@ Input:
 
 Command:
 ```sh
-format -i '(-?\d+) (-?\d+(?:.\d+)?)' -o '{1} + {2} = {1:%g:+(2)}'
+format -i '(-?\d+) (-?\d+(?:.\d+)?)' -o '{1} + {2} = {1::%g:+(2)}'
 ```
 
 Output:
@@ -279,7 +296,7 @@ Output of `ls`:
 
 Command:
 ```sh
-ls | format -i '(\d+)\.jpg' -o 'mv "{0}" "{1:%d:+1}.jpg"' | xargs -0 sh -c
+ls | format -i '(\d+)\.jpg' -o 'mv "{0}" "{1::%d:+1}.jpg"' | xargs -0 sh -c
 ```
 
 Output of `ls` afterwards:
@@ -320,7 +337,7 @@ Output of `ls`:
 
 Command:
 ```sh
-bulkrename '(\d+)\.jpg' '{1:%d:+1}.jpg'
+bulkrename '(\d+)\.jpg' '{1::%d:+1}.jpg'
 ```
 
 Output:
@@ -329,12 +346,12 @@ mv "000.jpg" "1.jpg"
 mv "001.jpg" "2.jpg"
 mv "002.jpg" "3.jpg"
 
-execute commands with 'bulkrename (\d+)\.jpg {1:%d:+1}.jpg exec'
+execute commands with 'bulkrename (\d+)\.jpg {1::%d:+1}.jpg exec'
 ```
 
 Command:
 ```sh
-bulkrename '(\d+)\.jpg' '{1:%d:+1}.jpg' exec
+bulkrename '(\d+)\.jpg' '{1::%d:+1}.jpg' exec
 ```
 
 Output of `ls` afterwards: