The parenthesis causes an extra shell to be executed.
All regular expression implementations that claim BRE (or higher) compatibility provide the last results of each separate match enclosed in parenthesis (officially called a subexpression but frequently called a submatch or group) in variables that may subsequently (after the regular expression has been executed) be used or substituted in an expression by using a backreference. There may be one or more such groupings in any regular expression. These variables are usually numbered $1 to $9. Where $1 will contain the first submatch, $2 will contain the second submatch and so on. The $x value typically persists until another regular expression is encountered. Examples:
You cannot use parenthesis to add additional commands.
In these examples, the parenthesis are used to specify a list:These show expressions:This is an example of creating a subshell:And this is an example of grouping:And here is an example where the parenthesis have two different meanings:I've tried to combine several of these uses into one statement, andit generates errors.
The solution is to place a dummy character before bothstrings:In complex expressions, parenthesis can be used to alter the defaultprecedence in evaluation.
Balanced parentheses parser Python - Stack Overflow
With the stronger emphasis by IM on image sequences, especially withinparenthesis, it is no surprise that a set of new image operators have beenprovided to manipulate the image lists. The arguments to these operators are numbers indexing the image list,starting with zero ('') for the first image, and one('') for the second image, and so on. However if you give anegative index, the images are referenced from the end (last image added) ofthe image list. That is a index of '' is the last image inthe current image list (generally the last image read or created),'' for the second last and so on.
The "" listoperator is the simplest of the image list operators, it just deletesimages from the current image list.
python - Parsing a parenthesis - Stack Overflow
This technique lets you follow what each step (wrapped in parenthesis) thevery complex command produced, and allows for easier debugging of each step inof a process.
parenthesis parser · jsPerf
As you can see, when the parenthesis ended, the font setting was restored tothe previous 'Candice' font, instead of the 'Gecko' font that was set withinthe parenthesis.
Parenthesis String Parser · GitHub
When given at the start of a IM command, it will cause parenthesis to alsosave and retrieve the previous settings that have been given. That means anysettings given within parenthesis, will only remain set, until the end of theparenthesis.
It may also be easier for image processing scripts to perform each processingstep as a separate parenthesis, as a means of separating the processing steps,it is applying.