A simple `qmv` implementation. Given a list of files as arguments, this program will open up a file in $EDITOR with one line per argument. You edit the file names, and then when you quit, the files are re-named according to their corresponding lines in the edited file.

Makefile

.PHONY: clean

CFLAGS = -Wall -Wextra -Wpedantic -Werror
bin = qmv

$(bin):

clean:
	rm $(bin)

qmv.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <stdarg.h>

#define ECODE 1
#define GETLINE_INIT 200

void pexit(char * n) {
    perror(n); exit(ECODE);
}

void * xmalloc(size_t size) {
    void * out = malloc(size);
    if (out == NULL) { pexit("malloc"); }
    return out;
}

void * xrealloc(void * ptr, size_t size) {
    void * out = realloc(ptr, size);
    if (out == NULL) { free(ptr); pexit("realloc"); }
    return out;
}

char * xgetline(FILE * f) {
    char current = 0;
    char * line = malloc(GETLINE_INIT);
    int bufsize = GETLINE_INIT;
    int csize = 0;
    for (; fread(&current, 1, 1, f) > 0; csize++) {
        if (csize >= bufsize) {
            bufsize *= 2;
            line = xrealloc(line, bufsize);
        }

        if (current == '\n') {
            break;
        } else {
            line[csize] = current;
        }
    }
    assert(csize < bufsize);
    line[csize++] = '\0';
    line = xrealloc(line, csize);
    return line;
}

int subcommand(char * command, ...) {
    va_list args;
    va_start(args, command);

    int bsize = strlen(command) + 1;
    char * buf = xmalloc(bsize);
    memcpy(buf, command, bsize);

    char * next = NULL;
    while ((next = va_arg(args, char *)) != NULL) {
        /* +1 for space, +2 for quotes. */
        bsize += strlen(next) + 3;
        buf = realloc(buf, bsize);
        strcat(buf, " \"");
        strcat(buf, next);
        strcat(buf, "\"");
    }
    va_end(args);

    int status = system(buf);
    free(buf);
    return status;
}

int main(int argc, char * argv[]) {
    char * editor = getenv("EDITOR");
    if (editor == NULL) {
        fprintf(stderr, "$EDITOR is not defined.\n");
        exit(ECODE);
    }

    char * tname = tmpnam(NULL);
    FILE * tfile = fopen(tname, "w");
    if (tfile == NULL) { pexit("fopen"); }

    for (int i = 1; i < argc; i++) {
        if (fwrite(argv[i], strlen(argv[i]), 1, tfile) < 1 ||
            fwrite("\n", 1, 1, tfile) < 1) {
            pexit("fwrite"); }
    }
    fclose(tfile);

    int status = subcommand(editor, tname, NULL);
    if (status != 0) {
        fprintf(stderr, "%s returned non-zero exit code: %d\n",
                editor, status);
        remove(tname);
        exit(ECODE);
    }

    tfile = fopen(tname, "r");
    if (tfile == NULL) { pexit("fopen"); }

    char *cline = NULL;
    for (int i = 1; i < argc; i++) {
        cline = xgetline(tfile);
        if (cline[0] == '\0') { 
            fprintf(stderr, 
                    "Instruction file had fewer lines than expected.\n");
            exit(ECODE);
        }
        if (strcmp(argv[i], cline) != 0) {
            int status = subcommand("mv", argv[i], cline, NULL);
            if (status != 0) { 
                fprintf(stderr, "'mv' failed with exit code: %d\n", status);
                exit(ECODE);
            }
        }
        free(cline);
    }
    fclose(tfile);
    remove(tname);
    return 0;
}