Positive Lookbehind and Lookahead to the end of string

Question

My string patterns looks like this: UNB+UNOC:3+4399945681577+_GLN_Company__+180101:0050+10870 and I am trying to extract everything after the second last + , ie 180101:0050+10870 .

Thus far, I managed to address the second last block 180101:0050 with this expression (?<=\\+)[^\\+]+(?=\\+[^\\+]*$) but fail to include the last block including the last +. Here is my sample: regex101

The expression is meant for R and I still need to escape the characters later on. This format it just for testing purposes in Regex101.

Answer 1

We could capture group based on the occurrence of + from the end ( $ ) of the string.

sub(".*\\+([^+]+\\+[^+]+$)", "\\1", str1)
#[1] "180101:0050+10870"

data

str1 <- "UNB+UNOC:3+4399945681577+_GLN_Company__+180101:0050+10870"

Answer 2

You may use

\+\K[^+]+\+[^+]*$

Or, if you would like to use it with stringr::str_extract :

(?<=\+)[^+]+\+[^+]*$

See the regex demo . Details:

• \\+ - a + char
• \\K - match reset operator
• (?<=\\+) - location right after a + symbol
• [^+]+ - one or more chars other than +
• \\+ - a +
• [^+]+ - one or more chars other than +
• $ - end of string.

See R demo online :

x <- "UNB+UNOC:3+4399945681577+_GLN_Company__+180101:0050+10870"
regmatches(x, regexpr("\\+\\K[^+]+\\+[^+]*$", x, perl=TRUE))
## => [1] "180101:0050+10870"
library(stringr)
str_extract(x, "(?<=\\+)[^+]+\\+[^+]*$")
## => [1] "180101:0050+10870"

Answer 3

Another way you can do in this case:

library(stringr)
str_extract("UNB+UNOC:3+4399945681577+_GLN_Company__+180101:0050+10870", "\\d+:\\d+\\+\\d+")
#"180101:0050+10870"