misc-c-utils

This is basically just a repository to host an assortment of small C programs I've written (and one I didn't), mostly as an aid to writing more portable shell scripts.

Some of these utilities are of my own design to simplify specific tasks. For instance:

• case-insensitive-pattern.c:

  • given a string (either given as command-line argument(s) or on standard input), prints out a regex pattern that can be used with sed and the like to match the string, ignoring case.
  • This can be useful because, while -i works to do these matches in POSIX grep, POSIX sed has no such provisions.
  • example text becomes [Ee][Xx][Aa][Mm][Pp][Ll][Ee] [Tt][Ee][Xx][Tt]

• killsuid.c:

  • A pedantically POSIX portable program to search for and kill wpa_supplicant and openvpn.
  • Unfortunately, this pedanticism means I have to parse 'ps' output.
  • Name comes from the fact that you might have to run this as root.
  • Not recommended for general usage, but I enjoyed writing the program.
  • One of the first programs in C that I haven't minded doing memory management in.
  • Written in C so that it can be made suid root if desired (shell scripts cannot in most implementations).
  • Note: this uses popen(), which is a relative of the system() call and which is known to have security issues. I didn't want to take the time to manually do the pipe(), fork(), execl() method.
  • source code contains a list of the possible return codes and what they all mean.

• quotify.c:

  • Somewhat intelligently replaces "double quotes" with “curly quotes” (in UTF-8).
  • Reads input from either a supplied file name or stdin (stdin is used if no arguments are passed or the argument - is passed).
  • This doesn't use any clever data structures to track the current state or anything, and it doesn't peek ahead, so it will fail if you have nested double quotes. Caveat emptor.
  • Handy for some simple cases, like while preparing text for conversion into an e-book.

• which.c:

  • This one I did not write; it was stolen from OpenBSD and modified just enough to compile without warnings on Linux. This was prompted by Debian removing the which shell script from debianutils. Their recommended replacement, command -v, has a handful of shortcomings regarding aliases, and also does not have an analogue for which -a.

    Also, since pretty much every free Unix for a long time has had which (going back to NetBSD in the 90's at least, and probably 3BSD), it seems like an unusual choice to remove. The man pages are also included (unaltered).

    The only thing I wrote for this was a Makefile, plus a few minor tweaks (under ten lines) to get rid of OpenBSD-isms (like pledge()). I also replaced one such OpenBSD-ism with a Linux-ism (getting the program name).

• wineify.c:

  • This one is highly specific and probably not well suited for any task. It tries to guess what that is being passed to it is a command-line flag and what isn't; if it doesn't think something's a command-line flag it assumes it is a filename and runs it through winepath -w, printing a null-terminated result (suitable for GNU xargs' xargs -0). This exists solely to wrap around Photoshop in wine so that I can pass it unix file names/paths and have them open properly. If something is probably not a filename, it gets passed through unchanged with a null terminator on the end. This also uses popen(), so it's pretty much as insecure as the system() call is. Don't use this unless you really understand what it is doing.

Others tools are inspired by GNU-only, BSD-only, and other system-specific programs or command options which I have found useful and wish to be able to replicate in scripts on a wider array of Unix-like machines.

Examples:

• sleep-decimal: pause for a number of seconds, which can be given in fractional seconds. POSIX sleep only guarantees second granularity.
  • GNU sleep can also idle for fractional seconds, but this is not a requirement for POSIX compliance and should not be counted on.
• realpath-posix.c: essentially a wrapper around POSIX's realpath() C function so it can be used in shell scripts.
  • GNU readlink can also do this with the -f parameter, but readlink is not a POSIX-defined program.
  • This should follow multiple symlinks until it finds an existing file or fails to resolve.

By the way, to this end (the ability to use the in shell scripts on many kinds of machines), all of these C programs (currently) target POSIX-compliant platforms, using only C standard library and POSIX-specified C functions.

I know this means Windows is left out in the cold, but if you really want to I'm certain they will still work in Cygwin. Some might even work in plain MinGW with the MS Visual C++ runtime, since not all of them even use POSIX functions at all. One gotcha might be having to make sure 'b' is included in the mode string for fopen() calls, since Windows/DOS historically have liked to mess with text files otherwise (mostly newline tampering). This has not been tested here, but is still a common problem in other C programs.