# Help in my own gsub design **URL:** \ **Category:** Ruby\ **Created:** [October 2, 2007, 1:41pm UTC](https://www.ruby-forum.com/t/help-in-my-own-gsub-design/116109 "2007-10-02T13:41:19Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Josselin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de0a6/32.png) [@Josselin](https://www.ruby-forum.com/u/Josselin)\ **Post date:** [October 2, 2007, 1:41pm UTC](https://www.ruby-forum.com/t/help-in-my-own-gsub-design/116109/1 "2007-10-02T13:41:19Z")
I don’t use it very often, rather copying from example, but it’s so useful that I should learn how to write it I’d appreciate any guru tip on how to proceed once the problem is on the paper : example : INPUT STRINGS 1- input can contains spaces (should be eliminated) 2- good patterns : 2a- an Integer like 99 (no limit) a \> \>= \< \<= \<\> != followed by an Integer like \>99 > =99 \<99 \<=99 \<\>99 !=99 2b- a String like: abcd abc99 99abc a99bc 2c- a % sign followed by a String like %abcd %abc99 %99abc %a99bc %abcd 2d- a String followed by a % sign like abcd% abc99% 99abc% a99bc% 2e- a String leading containing or ending with, one or many \* sign(s) like a_bcd a\*\*bc99 99_a_bc a99bc a99bca99bca9\*\*9bc_ 3-any other pattern will be considered as wrong OUTPUTS 2a -\> an array [characters, Integer] like [“\<\>”, 99] 2b, 2c, 2d,2e -\> an array [nil, String] like [nil, abcd] or [nil, %abcd] or [nil, a99bc%] or [nil, _a9\*\*9b_c] I am interesting in understanding the design process… : how should I start when designing such gsub routine ? should I state it differently on paper first ? well, any tip that can help me to build the next ones… thanks for your support joss ---
**Author:** ![Josselin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de0a6/32.png) [@Josselin](https://www.ruby-forum.com/u/Josselin)\ **Post date:** [October 2, 2007, 2:50pm UTC](https://www.ruby-forum.com/t/help-in-my-own-gsub-design/116109/2 "2007-10-02T14:50:38Z")
On Oct 2, 6:35 am, Josselin [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ``` > like %abcd %abc99 %99abc %a99bc %abcd > > ``` > > joss def foo s case s when /^(\>|\>=|\<|\<=|\<\>|!=)?(\d+)$/ [$1 || “”, $2.to\_i] when /^(%)?[a-z\d]+(%)?$/ return nil if 1 != $~.captures.compact.size [nil, $&] when /^(?=.\*\*)[\*a-z\d]+$/ [nil, $&] end end p foo( “88” ) p foo( “\<\>88” ) p foo( “%33” ) p foo( “33%” ) p foo( “a\*9” ) p foo( ‘bat’ ) ---
**Author:** ![Josselin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de0a6/32.png) [@Josselin](https://www.ruby-forum.com/u/Josselin)\ **Post date:** [October 2, 2007, 3:25pm UTC](https://www.ruby-forum.com/t/help-in-my-own-gsub-design/116109/3 "2007-10-02T15:25:53Z")
On 2007-10-02 14:46:48 +0200, William J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) said: > > 1- input can contains spaces (should be eliminated) > > 2c- a % sign followed by a String > > OUTPUTS > > thanks for your support > > when /^(?=.\*\*)[\*a-z\d]+$/ > > [nil, $&] > > end > > end > > p foo( “88” ) > p foo( “\<\>88” ) > p foo( “%33” ) > p foo( “33%” ) > p foo( “a\*9” ) > p foo( ‘bat’ ) thanks a lot , William, I can see how you built it… I just have 2 points to clarify if you don’t mind 1- return nil if 1 != $~.captures.compact.size I don’t catch up 2- (?=.\*\*) otherwise I commented it … is my understanding correct ? def foo s case s when /^(\>|\>=|\<|\<=|\<\>|!=)?(\d+)$/ # start with \> OR \>= OR \< OR \<= OR \<\> OR != (0 or 1 time) then digit(0-9) n times [$1 || “”, $2.to\_i] # first element or nil , second element to integer ``` when /^(%)?[a-z\d]+(%)?$/ ``` # start with % ( 0 or 1 time) then characters a-zA-Z 1 or n times then end with % ( 0 or 1 time) return nil if 1 != $~.captures.compact.size # return nil if … ``` [nil, $&] ``` # first element nil, second element = parameter ``` when /^(?=.*\*)[*a-z\d]+$/ ``` # start with \*( 0 or n times)… then characters \*a-zA-Z 1 or n tiems [nil, $&] # first element nil, second element = parameter end end ---
**Author:** ![Josselin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de0a6/32.png) [@Josselin](https://www.ruby-forum.com/u/Josselin)\ **Post date:** [October 2, 2007, 5:35pm UTC](https://www.ruby-forum.com/t/help-in-my-own-gsub-design/116109/4 "2007-10-02T17:35:39Z")
On Oct 2, 10:12 am, William J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > This is a good point. Instead of $& (what was matched by the reg.ex.) > I should > have used the parameter of the function, s. But s may have unwanted spaces. Stick with $&. ---
**Author:** ![Josselin](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9de0a6/32.png) [@Josselin](https://www.ruby-forum.com/u/Josselin)\ **Post date:** [October 2, 2007, 5:16pm UTC](https://www.ruby-forum.com/t/help-in-my-own-gsub-design/116109/5 "2007-10-02T17:16:14Z")
On Oct 2, 8:24 am, Josselin [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > INPUT STRINGS > > > 2b- a String like: abcd abc99 99abc a99bc > > > 3-any other pattern will be considered as wrong > > > help me to build the next ones… > > > return nil if 1 != $~.captures.compact.size > > > p foo( “a\*9” ) > > > p foo( ‘bat’ ) > > thanks a lot , William, I can see how you built it… I just have 2 > points to clarify if you don’t mind > > 1- return nil if 1 != $~.captures.compact.size > I don’t catch up I wrote the function so that it will return nil if the string doesn’t match your patterns. The line above is equivalent to if 1 != $~.captures.compact.size return nil end The number of succesful captures (captured by /^(%)?[a-z\d]+(%)?$/ ) must be exactly 1; i.e., the string must begin or end with %, but not both. > 2- (?=.\*\*) (?=…) is a zero-width look-ahead; it looks ahead but it doesn’t move ahead in the string. I put this here to make sure that the string contains at least one \*. > otherwise I commented it … is my understanding correct ? > > def foo s > case s I forgot about spaces. If they can only be at the start or end of the string, use case s.strip > ``` > when /^(>|>=|<|<=|<>|!=)?(\d+)$/ > # start with > OR >= OR < OR <= OR <> OR != (0 or 1 time) then > > ``` > > digit(0-9) n times 1 or more times. > ``` > [$1 || "", $2.to_i] > # first element or nil , second element to integer > > ``` If 1st capture is nil, use “”; else use 1st capture. > ``` > when /^(%)?[a-z\d]+(%)?$/ > # start with % ( 0 or 1 time) then characters a-zA-Z 1 or n times then > > ``` > > end with % ( 0 or 1 time) > return nil if 1 != $~.captures.compact.size > # return nil if … > [nil, $&] > # first element nil, second element = parameter This is a good point. Instead of $& (what was matched by the reg.ex.) I should have used the parameter of the function, s.