Find Unique Characters in a File

Question

I have a file with 450,000+ rows of entries. Each entry is about 7 characters in length. What I want to know is the unique characters of this file.

For instance, if my f

Answer 1

BASH shell script version (no sed/awk):

while read -n 1 char; do echo "$char"; done < entry.txt | tr [A-Z] [a-z] |  sort -u

UPDATE: Just for the heck of it, since I was bored and still thinking about this problem, here's a C++ version using set. If run time is important this would be my recommended option, since the C++ version takes slightly more than half a second to process a file with 450,000+ entries.

#include 
#include 

int main() {
    std::set seen_chars;
    std::set::const_iterator iter;
    char ch;

    /* ignore whitespace and case */
    while ( std::cin.get(ch) ) {
        if (! isspace(ch) ) {
            seen_chars.insert(tolower(ch));
        }
    }

    for( iter = seen_chars.begin(); iter != seen_chars.end(); ++iter ) {
        std::cout << *iter << std::endl;
    }

    return 0;
}

Note that I'm ignoring whitespace and it's case insensitive as requested.

For a 450,000+ entry file (chars.txt), here's a sample run time:

[user@host]$ g++ -o unique_chars unique_chars.cpp 
[user@host]$ time ./unique_chars < chars.txt
a
b
d
o
y

real    0m0.638s
user    0m0.612s
sys     0m0.017s