High Level Program Structure

• serialize/marshalling: transform a stream of bytes to in-memory data structures
• deserialize/demarshalling: transform in-memory data structures to a stream of bytes

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Code Structure

Common Unix interface design patterns have common code structures associated with them.

The Filter Pattern

Read data on standard input, transform it in some way, and write the results to standard output

Standard Variation

when output can be produced after reading a single item

Examples: tr (by character), grep (by line)

int main(int argc, char *argv[]) {
    /* variable declarations */

    /* CLA parsing */

    while (( /* deserialize one item */ ) != EOF) {
        /* central algorithm */
        /* serialize one item */;
    }
}

Sponge Variation

when all data must be read before any output can be produced

Examples: sort, wc, wordfreq

int main(int argc, char *argv[]) {
    /* variable declarations */

    /* CLA parsing */

    while (( /* deserialize one item */ ) != EOF) {
        /* insert item into data structure */
    }

    /* central algorithm */
    /* serialize list of items */;
}

catlike pattern

Some filters can read input from a list of files named on the command line instead of reading from standard input Examples: cat

int main(int argc, char *argv[]) {
    FILE* fp;
    /* variable declarations */

    /* CLA parsing */

    if ( /* there are file name arguments */ ) {
        while ( /* there are still file names in argv */ ) {
            fp = fopen(...);
            /* filter pattern using fp as input */
        }
    } else {
        /* filter pattern using standard input as input */
    }
}

Note: A catlike filter pattern may utilize the standard variation or the sponge variation.