user
Create a routine that, given a set of strings representing directory paths and a single character directory separator, will return a string representing that part of the directory tree that is common to all the directories.

Test your routine using the forward slash '/' character as the directory separator and the following three strings as input paths:

```
     '/home/user1/tmp/coverage/test'
     '/home/user1/tmp/covert/operator'
     '/home/user1/tmp/coven/members'

```

Note: The resultant path should be the valid directory `'/home/user1/tmp'` and not the longest common string `'/home/user1/tmp/cove'`.

If your language has a routine that performs this function (even if it does not have a changeable separator character), then mention it as part of the task.

Other tasks related to string operations:

Metrics

* Array length
* String length
* Copy a string
* Empty string  (assignment)

Counting

* Word frequency
* Letter frequency
* Jewels and stones
* I before E except after C
* Bioinformatics/base count
* Count occurrences of a substring
* Count how many vowels and consonants occur in a string

Remove/replace

* XXXX redacted
* Conjugate a Latin verb
* Remove vowels from a string
* String interpolation (included)
* Strip block comments
* Strip comments from a string
* Strip a set of characters from a string
* Strip whitespace from a string -- top and tail
* Strip control codes and extended characters from a string

Anagrams/Derangements/shuffling

* Word wheel
* ABC problem
* Sattolo cycle
* Knuth shuffle
* Ordered words
* Superpermutation minimisation
* Textonyms (using a phone text pad)
* Anagrams
* Anagrams/Deranged anagrams
* Permutations/Derangements

Find/Search/Determine

* ABC words
* Odd words
* Word ladder
* Semordnilap
* Word search
* Wordiff  (game)
* String matching
* Tea cup rim text
* Alternade words
* Changeable words
* State name puzzle
* String comparison
* Unique characters
* Unique characters in each string
* Extract file extension
* Levenshtein distance
* Palindrome detection
* Common list elements
* Longest common suffix
* Longest common prefix
* Compare a list of strings
* Longest common substring
* Find common directory path
* Words from neighbour ones
* Change e letters to i in words
* Non-continuous subsequences
* Longest common subsequence
* Longest palindromic substrings
* Longest increasing subsequence
* Words containing "the" substring
* Sum of the digits of n is substring of n
* Determine if a string is numeric
* Determine if a string is collapsible
* Determine if a string is squeezable
* Determine if a string has all unique characters
* Determine if a string has all the same characters
* Longest substrings without repeating characters
* Find words which contains all the vowels
* Find words which contain the most consonants
* Find words which contains more than 3 vowels
* Find words whose first and last three letters are equal
* Find words with alternating vowels and consonants

Formatting

* Substring
* Rep-string
* Word wrap
* String case
* Align columns
* Literals/String
* Repeat a string
* Brace expansion
* Brace expansion using ranges
* Reverse a string
* Phrase reversals
* Comma quibbling
* Special characters
* String concatenation
* Substring/Top and tail
* Commatizing numbers
* Reverse words in a string
* Suffixation of decimal numbers
* Long literals, with continuations
* Numerical and alphabetical suffixes
* Abbreviations, easy
* Abbreviations, simple
* Abbreviations, automatic

Song lyrics/poems/Mad Libs/phrases

* Mad Libs
* Magic 8-ball
* 99 bottles of beer
* The Name Game (a song)
* The Old lady swallowed a fly
* The Twelve Days of Christmas

Tokenize

* Text between
* Tokenize a string
* Word break problem
* Tokenize a string with escaping
* Split a character string based on change of character

Sequences

* Show ASCII table
* De Bruijn sequences
* Summarize and say sequence
* Generate lower case ASCII alphabet
assistant
(formerly Perl 6)

```
my $sep = '/';
my @dirs = </home/user1/tmp/coverage/test
            /home/user1/tmp/covert/operator
            /home/user1/tmp/coven/members>;

my @comps = @dirs.map: { [ .comb(/ $sep [ <!before $sep> . ]* /) ] }; 

my $prefix = '';

while all(@comps[*]»[0]) eq @comps[0][0] {
    $prefix ~= @comps[0][0] // last;
    @comps».shift;
}

say "The longest common path is $prefix";

```

Output:

```
The longest common path is /home/user1/tmp

```

If you'd prefer a pure FP solution without side effects, you can use this:

```
my $sep := '/';
my @dirs := </home/user1/tmp/coverage/test
             /home/user1/tmp/covert/operator
             /home/user1/tmp/coven/members>;

my @comps = @dirs.map: { [ .comb(/ $sep [ <!before $sep> . ]* /) ] };

say "The longest common path is ",
    gather for 0..* -> $column {
        last unless all(@comps[*]»[$column]) eq @comps[0][$column];
        take @comps[0][$column] // last;
    }

```

Or here's another factoring, that focuses on building the result with cumulative sequences and getting the solution with `first`:

```
my $sep = '/';
my @dirs = </home/user1/tmp/coverage/test
            /home/user1/tmp/covert/operator
            /home/user1/tmp/coven/members>;

sub is_common_prefix { so $^prefix eq all(@dirs).substr(0, $prefix.chars) }

say ([\~] @dirs.comb(/ $sep [ <!before $sep> . ]* /)).reverse.first: &is_common_prefix

```