What is the difference between and - in ERB in Rails

Question

Can some one please describe the usage of the following characters which is used in ERB file    lt       gt   lt       gt   lt    -  gt   lt       gt    what s the usage of each one

User · Answer

These are use in ruby on rails    -   lt         -  The  lt      tags are used to execute Ruby code that does not return anything  such as conditions  loops or blocks  Eg  -   lt h1 gt Names of all the people lt  h1 gt   lt    people each do  person    gt    Name   lt    person name   gt  lt br gt   lt   end   gt     lt        -  use to display the content    Name   lt    person name   gt  lt br gt     lt    -   -  Rails extends ERB  so that you can suppress the newline simply by adding a trailing hyphen to tags in Rails templates   lt       -  comment out the code   lt    WRONG   gt  Hi  Mr   lt   puts  Frodo    gt

User · Answer

lt     gt   Executes the ruby code within the brackets   lt      gt   Prints something into erb file   lt       gt   Equivalent to  lt    raw   gt   Prints something verbatim  i e  w o escaping  into erb file   Taken from Ruby on Rails Guides    lt   -  gt   Avoids line break after expression   lt      gt   Comments out code within brackets  not sent to client  as opposed to HTML comments   Visit Ruby Doc for more infos about ERB

User · Answer

lt     gt  and  lt  - and -  gt  are for any Ruby code  but doesn t output the results  e g  if statements   the two are the same    lt      gt  is for outputting the results of Ruby code   lt      gt  is an ERB comment  Here s a good guide  http   api rubyonrails org classes ActionView Base html

User · Answer

lt     gt    Executes the ruby code    lt      gt    Prints into Erb file  Or browser    lt   -  gt    Avoids line break after expression     lt      gt    ERB comment

User · Answer

Rails does not use the stdlib s ERB by default  it uses erubis  Sources  this dev s comment  ActionView s gemspec  accepted merge request I did while writing this   There are behavior differences between them  in particular on how the hyphen operators  - and -  work   Documentation is scarce  Where is Ruby  39 s ERB format  quot officially quot  defined  so what follows are empirical conclusions   All tests suppose   require  erb  require  erubis    When you can use -   ERB  you must pass - to trim mode option of ERB new to use it  erubis  enabled by default    Examples   begin ERB new   lt     a  -  gt  nb   result  rescue SyntaxError   else raise  end ERB new   lt     a  -  gt  nb     nil   -    result     ab   or raise Erubis  Eruby new   lt     a  -  gt    n b   result     a b  or raise   What -  does    ERB  remove the next character if it is a newline  erubis    in  lt     gt   without     - is useless because  lt     gt  and  lt   -  gt  are the same   lt     gt  removes the current line if it only contains whitespaces  and does nothing otherwise  in  lt    -  gt   with       remove the entire line if it only contains whitespaces else  if there is a non-space before the tag  and only whitesapces after  remove the whitespces that come after else  there is a non-space after the tag  do nothing     Examples     Remove ERB new  a  nb  lt   0 -  gt  n c   nil   -   result     a  nb  c  or raise    Don t do anything  not followed by newline  but by space  ERB new  a n lt   0 -  gt   nc   nil   -   result     a nb  nc  or raise    Remove the current line because only whitesapaces  Erubis  Eruby new    lt   0   gt   nb   result     b  or raise    Same as above  thus useless because longer  Erubis  Eruby new    lt   0 -  gt   nb   result     b  or raise    Don t do anything because line not empty  Erubis  Eruby new  a  lt   0   gt   nb   result     a   nb  or raise Erubis  Eruby new    lt   0   gt  a nb   result       a nb  or raise Erubis  Eruby new    lt   0 -  gt  a nb   result       a nb  or raise    Don t remove the current line because of      Erubis  Eruby new    lt    0   gt   nb   result      0  nb  or raise    Remove the current line even with      Erubis  Eruby new    lt    0 -  gt   nb   result      0b    or raise    Remove forward only because of  -  and non space before  Erubis  Eruby new  a  lt    0 -  gt   nb   result     a 0b    or raise    Don t do anything because non-whitespace forward  Erubis  Eruby new    lt    0 -  gt  a nb   result      0 a nb    or raise   What  - does    ERB  remove whitespaces before tag and after previous newlines  but only if there are only whitespaces before  erubis  useless because  lt  -   gt  is the same as  lt     gt   without     and this cannot be used with   which is the only case where -  can be useful  So never use this    Examples     Remove ERB new  a  n   lt  - 0   gt  b n c   nil   -   result     a  n b n c  or raise    b is not whitespace  do nothing  ERB new  a  nb   lt  - 0   gt  c n d   nil   -   result     a  nb   c n d  or raise   What  - and -  do together  The exact combination of both effects separately

User · Answer

I ve added the  lt    literal tag delimiter as an answer to this because of its obscurity   This will tell erb not to interpret the  lt   part of the tag which is necessary for js apps like displaying chart js tooltips etc   Update  Fixed broken link    Everything about ERB can now be found here  https   puppet com docs puppet 5 3 lang template erb html tags

User · Answer

lt       gt  executes the code in there but does not print the result  for eg  We can use it for if else in an erb file      lt   temp   1   gt   lt   if temp    1  gt    temp is 1  lt   else   gt    temp is not 1  lt  end  gt      Will print temp is 1     lt       gt  executes the code and also prints the output  for eg  We can print the value of a rails variable    lt   temp   1   gt   lt    temp   gt      Will print 1     lt    -  gt  It makes no difference as it does not print anything  -  gt  only makes sense with  lt    -  gt   this will avoid a new line      lt       gt  will comment out the code written within this

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