Search a file for lines matching a regular expression pattern. Return the line number and contents of each matching line.
The Unix grep command can be used to search
for lines in one or more files that match a user-provided search query (known as the pattern).
The grep command takes three arguments:
Your task is to implement the grep function, which should read the contents
of the specified files, find the lines that match the specified pattern
and then output those lines as a single string. Note that the lines should
be output in the order in which they were found, with the first matching line
in the first file being output first.
As an example, suppose there is a file named “input.txt” with the following contents:
hello
world
hello again
If we were to call grep "hello" input.txt, the returned string should be:
hello
hello again
As said earlier, the grep command should also support the following flags:
-n Print the line numbers of each matching line.-l Print only the names of files that contain at least one matching line.-i Match line using a case-insensitive comparison.-v Invert the program – collect all lines that fail to match the pattern.-x Only match entire lines, instead of lines that contain a match.If we run grep -n "hello" input.txt, the -n flag will require the matching
lines to be prefixed with its line number:
1:hello
3:hello again
And if we run grep -i "HELLO" input.txt, we’ll do a case-insensitive match,
and the output will be:
hello
hello again
The grep command should support multiple flags at once.
For example, running grep -l -v "hello" file1.txt file2.txt should
print the names of files that do not contain the string “hello”.
Requires a properly installed Java 11 JDK (with JAVA_HOME correctly set).
# On linux or macOS
./gradlew test
# On Windows
./gradlew.bat test