Javascript正则表达式：只匹配文本的结尾

Question

I would like to find out multiline texts ending with "Tr ", "Br " and linebreak ("\\n") without " _" (none-whitespace and underscore) preceded. Exmples

Text 1:

Command1 Br 
Command2 Tr 

"Command1 Br \nCommand2 Tr " //match "Tr " at the end

Text 2:

Command3 con Tr 
Command4 Br 

"Command3 con Tr \nCommand4 Br " //match "Br " at the end

Text 3:

Command2 Tr 
Command3 con Br 
Command4 C_

"Command2 Tr \nCommand3 con Br \nCommand4 C_\n" //match "\n" at the end after C_

Text 4:

Command1 Tr 
Command1 Br 
Command2 Tr _

"Command1 Tr \nCommand1 Br \nCommand2 Tr _\n" //no match because of " _" preceded "\n"

Text 5:

Command1 Tr 
Command1 Br 
Command2 mt

"Command1 Tr \nCommand1 Br \nCommand2 mt\n" //match \n at the end after "mt"

Text 6:

Command2 ht

"\n\nCommand2 ht\n" //match \n at the end after "ht"

Answer 1

You may use the following regex to extract those matches:

/(?:^| [^_]|[^ ]_|[^ ][^_])([BT]r|\n)[\t ]*$/

See the regex demo .

Details :

• (?:^| [^_]|[^ ]_|[^ ][^_]) - a non-capturing group matching one of the three alternatives:
  • ^ - start of a line
  • | - or
  • [^_] - space and any char but _
  • | - or
  • [^ ]_ - any char but space and _
  • | - or
  • [^ ][^_] - any char but space and then any char but _ (thus, no space + _ )
• ([BT]r|\\n) - Capturing group 1: either Br , Tr or a newline symbol
• [\\t ]* - 0+ horizontal whitespaces (may be replaced with [^\\S\\r\\n] for better hor. whitespace coverage)
• $ - the very end of the string.

 var ss = ["Command1 Br \\nCommand2 Tr ", "Command3 con Tr \\nCommand4 Br ", "Command2 Tr \\nCommand3 con Br \\nCommand4 C_\\n", "Command1 Tr \\nCommand1 Br \\nCommand2 Tr _\\n", "Command1 Tr \\nCommand1 Br \\nCommand2 mt\\n", "\\n\\nCommand2 ht\\n"]; var rx = /(?:^| [^_]|[^ ]_|[^ ][^_])([BT]r|\\n)[\\t ]*$/; for (var s of ss) { console.log("Looking for a match in: " + s); m = rx.exec(s); if (m) { console.log("Found: " + JSON.stringify(m[1], 0, 4)); } else { console.log("No Match Found."); } }