Contents

Search a file for lines matching a regular expression pattern. Return the line
number and contents of each matching line.

The Unix [`grep`](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html) 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:

1. The pattern used to match lines in a file.
2. Zero or more flags to customize the matching behavior.
3. One or more files in which to search for matching lines.

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:

```text
hello
world
hello again
```

If we were to call `grep "hello" input.txt`, the returned string should be:

```text
hello
hello again
```

### Flags

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:

```text
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:

```text
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".

Version data entries

139 entries across 139 versions & 1 rubygems

Version	Path
trackler-2.2.1.180	problem-specifications/exercises/grep/description.md
trackler-2.2.1.179	problem-specifications/exercises/grep/description.md
trackler-2.2.1.178	problem-specifications/exercises/grep/description.md
trackler-2.2.1.177	problem-specifications/exercises/grep/description.md
trackler-2.2.1.176	problem-specifications/exercises/grep/description.md
trackler-2.2.1.175	problem-specifications/exercises/grep/description.md
trackler-2.2.1.174	problem-specifications/exercises/grep/description.md
trackler-2.2.1.173	problem-specifications/exercises/grep/description.md
trackler-2.2.1.172	problem-specifications/exercises/grep/description.md
trackler-2.2.1.171	problem-specifications/exercises/grep/description.md
trackler-2.2.1.170	problem-specifications/exercises/grep/description.md
trackler-2.2.1.169	problem-specifications/exercises/grep/description.md
trackler-2.2.1.167	problem-specifications/exercises/grep/description.md
trackler-2.2.1.166	problem-specifications/exercises/grep/description.md
trackler-2.2.1.165	problem-specifications/exercises/grep/description.md
trackler-2.2.1.164	problem-specifications/exercises/grep/description.md
trackler-2.2.1.163	problem-specifications/exercises/grep/description.md
trackler-2.2.1.162	problem-specifications/exercises/grep/description.md
trackler-2.2.1.161	problem-specifications/exercises/grep/description.md
trackler-2.2.1.160	problem-specifications/exercises/grep/description.md