Mitch Richling: Example UNIX Programs

Here you will find several examples of source code intended to illustrate concepts related to UNIX system programming – in C, Perl, and Ruby.

Get it all on github: https://github.com/richmit/ex-aupg/

suid0tmp.c

This is a little snippet of code I start with when making SUID0 programs

mjrrsh.pl

This little perl script demonstrates how to make perl do TCP/IP, how to make Perl timeout, and how rsh really works.

rssu.c

Demonstrates a very bad way to replace su.

forknwait.c

How to fork and, more importantly, how to wait.

forkbunny.c

This tiny program demonstrates how some UNIX systems allow a process to have an unlimited number of children.

passwd.c, passwd.pl, & passwd.rb

Demonstrates how to traverse the password database in a portable way.

group.c, group.pl, & group.rb

Demonstrates how to traverse the entire UNIX group database.

uideuid.c, uideuid.pl, & uideuid.rb

Demonstrates how to query the current user ID.

gidegid.c, gidegid.pl, & gidegid.rb

Demonstrates how to query the current group ID.

getgrXXX.c

Demonstrates how to look up group information by GID and/or gname (group name)

getpwXXX.c

Demonstrates how to look up password information by UID and/or uname (user name)

getgroups.c

Demonstrates how to find out what secondary groups the current user is in.

passwdshadow.c

Demonstrates how to obtain shadow password database information in a portable way.

env.c, env.pl, & env.rb

This bit of code shows how to query and change environment variables.

environ.c

How to use the environ variable defined by ISO C

arguments.c, arguments.pl, & arguments.rb

Demonstrates how to access the arguments given to a program.

kill.c, kill.pl, & kill.rb

Demonstrates how to send signals.

signal.c

Demonstrates several signal concepts using the BSD signal(3) API.

sleep.c, & sleep.pl

Demonstrates the correct way to get sleep to make your program suspend for a given amount of time.

sigaction.c

Demonstrate the sigaction system call.

IOerrors.c

Demonstrates the correct way to deal with errors from UNIX I/O functions.

fileIO.c

Demonstrates how to use the UNIX API to do file I/O.

sparse.c

This program demonstrates how to create a sparse file. Also called a "file with holes".

fileStuff.c

Several file operations are demonstrated

utime.c, utime.pl, & utime.rb

Simple demo of the utime function (the API equivalent of the touch command)

fileData.c

Demonstrates the stat call to discover various bits of info about files.

select_poll.c

Demonstrates the select system call.

flock_ex.c

Demonstrate file locking with the flock system call.

mmap.c

How to use the mmap function (SysV & POSIX) on a file.

readdir.c, readdir.pl, & readdir.rb

Demonstrates how read a UNIX directory(the file names in a subdirectory).

glob.pl, glob.rb

Typical way to do a readdir-type operation in perl and ruby.

dirRec.c

Demonstrates the classical recursive algorithm to traverse a directory tree (lots of open file descriptors)

dirDepth.c & dirDepthC.cpp

Demonstrates a method to do a depth first directory tree traversal (one open file descriptor and a linked list).

dirFastC.cpp

Like dirDepthC.cpp, but modified for a single ended container (no linked list) for performance

dirThreadCPP98.cpp

Demonstrates a threaded method (pthreads) for tree traversal

dirThreadCPP11.cpp

Demonstrates a threaded method (<span style='color: #f00;'>C++11</span> threads) for tree traversal

unixSocC.c

Demonstrates how to write a UNIX domain socket client.

unixSocS.c

Demonstrates how to write a UNIX domain socket server.

inetSocC.c

Demonstrates how to write a Internet domain socket client.

inetSocS.c

Demonstrates how to write a Internet domain socket server.

ptCond.c

How to use condition variables

ptJoin.c

Demonstrates the pthread_join system call

ptMutex.c

How to use mutexes

mtUtils.c & mtUtils.h

C, and C++, utilities for multi-threaded programs

hosts.c

Demonstrates how to query the current host name and how to look hosts up with the system's resolver.

fqdns.c, fqdns.pl, fqdns.rb, & fqdns.sh

How to get the FQDNS of a host – this is tricky! The shell version is just silly, but it will give you some ideas regarding how to make this work.

solaris_ps.c

Demonstrates how to use the Solaris procfs to access process information

rpacct.pl

Demonstrates how to parse Solaris process accounting records in perl.

shmMake.c

How to create a shared memory segment.

shmUse.c

How to attach to an existing memory segment, map it, and read data out of it.

shmRemove.c

How to remove a shared memory segment.

shmMakeAndUseRT.c

How to create a new shared memory segment, and how to use an existing one.

shmRemoveRT.c

How to remove a shared memory segment.

termSizeWatch.c

How to detect the current TTY's window size and monitor size changes

curHello.c, curHelloMV.c , curHelloW.c, & curHelloMVW.c

Simple examples of minimal, "hello, world!" programs for curses

curColor.c

How to use color.

curDraw.c

Demonstrates several ncurses functions via an ASCII art drawing program

curInput.c

How to do non-line buffered input and identify input keys.

paths.c

How to use the paths.h include file available on many UNIX systems.

param.c

How to use the param.h include file available some UNIX systems.

sysconf.c

How to use the sysconf function.

isocLimits.c

How to discover various properties of C types.

posixLimits.c

Demonstrates several limits.h constants provided by POSIX

uname.c & uname.sh

How to use the POSIX uname system call, and the /usr/bin/uname command.

regex_example.c

Simple example of standard UNIX regular expressions.

pcre_example.c

Simple example of the PCRE (Perl Compatible Regular Expressions) library

isoTokEx.c

An example of how to use strtok() and strtok_r().

popenDemo.c

An example of how to use the popen function.

getoptP.c

Minimal example of the getopt function call.

rlimit.c

Example of getrlimit – of ulimit and limit fame.

rlEX.c

Minimal example of readline use.

rlEXH.c & rlEXC.c

Extends the minimal example with custom completions (GNU Readline).

mkGDBM.c

Create a simple GDBM database.

rdGDBM.c

Read in and display the GDBM database created by mkGDBM.c.