Likewise, the parentheses are not needed at all as they serve no function in the pattern. Since regular expressions matches on substrings, as opposed to filename globbing patterns which are always automatically anchored, neither of the. This is better written as ] or as the range (in the POSIX standard locale). It first of all uses a non-standard expression to match a digit, \d. You then applied this in searching for matches in both the files mentioned on the command line.Ī secondary issue was the \\d in the pattern.txt file, which matches a backslash followed by the character d, i.e. This means that -e -f will be interpreted as "the regular expression to use is -f". The -e option is used for explicitly saying "the next argument is the expression". The issue with your command was that you used -e -f. ![]() I.e., search in line.txt for lines matching any of the extended regular expressions listed in pattern.txt, which, given the data in the question, produces This order was placed for QT3000! OK? ![]() Then, using it with GNU grep would be a matter of grep -E -f pattern.txt line.txt The captured subsequence may be used later in the expression, via a back reference, and may also be retrieved from the matcher once the match operation is complete.Īssuming that the pattern in pattern.txt is (.*)(\d )(.*) Group zero always stands for the entire expression.Ĭapturing groups are so named because, during a match, each subsequence of the input sequence that matches such a group is saved. In the expression ((A)(B(C))), for example, there are four such groups: Perhaps grep doesn't have such notion as: Groups and capturingĬapturing groups are numbered by counting their opening parentheses from left to right. Utilizing something similar to m.group(0) from a tutorial on regex. This order was placed for QT3000! regex]$ Using line.txt and pattern.txt as below: regex]$ grep -e -f pattern.txt regex]$ cat regex]$ cat line.txt Or Found value: This order was placed for QT300 How would I get this output: Found value: This order was placed for QT3000! OK?
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