#!/bin/bash# dev-tcp.sh: /dev/tcp redirection to check Internet connection.# Script by Troy Engel.# Used with permission. TCP_HOST=news-15.net   # A known spam-friendly ISP.TCP_PORT=80 # Port 80 is http.  # Try to connect. (Somewhat similar to a 'ping' . . .) echo "HEAD / HTTP/1.0" >/dev/tcp/${TCP_HOST}/${TCP_PORT}MYEXIT=$?: <<EXPLANATIONIf bash was compiled with --enable-net-redirections, it has the capability ofusing a special character device for both TCP and UDP redirections. Theseredirections are used identically as STDIN/STDOUT/STDERR. The device entriesare 30,36 for /dev/tcp:  mknod /dev/tcp c 30 36>From the bash reference:/dev/tcp/host/port If host is a valid hostname or Internet address, and port is an integerport number or service name, Bash attempts to open a TCP connection to thecorresponding socket.EXPLANATION   if [ "X$MYEXIT" = "X0" ]; then  echo "Connection successful. Exit code: $MYEXIT" else  echo "Connection unsuccessful. Exit code: $MYEXIT" fiexit $MYEXIT

#!/bin/bash# music.sh# Music without external files# Author: Antonio Macchi# Used in ABS Guide with permission.#  /dev/dsp default = 8000 frames per second, 8 bits per frame (1 byte),#+ 1 channel (mono)duration=2000   # If 8000 bytes = 1 second, then 2000 = 1/4 second.volume=$'xc0'  # Max volume = xff (or x00).mute=$'x80' # No volume = x80 (the middle).function mknote ()  # $1=Note Hz in bytes (e.g. A = 440Hz ::{   #+ 8000 fps / 440 = 16 :: A = 16 bytes per second)  for t in `seq 0 $duration`  do test $(( $t % $1 )) = 0 && echo -n $volume || echo -n $mute  done}e=`mknote 49`g=`mknote 41`a=`mknote 36`b=`mknote 32`c=`mknote 30`cis=`mknote 29`d=`mknote 27`e2=`mknote 24`n=`mknote 32767`# European notation.echo -n "$g$e2$d$c$d$c$a$g$n$g$e$n$g$e2$d$c$c$b$c$cis$n$cis$d $n$g$e2$d$c$d$c$a$g$n$g$e$n$g$a$d$c$b$a$b$c" > /dev/dsp# dsp = Digital Signal Processorexit  # A "bonny" example of an elegant shell script!

#!/bin/bash# pid-identifier.sh:# Gives complete path name to process associated with pid.ARGNO=1  # Number of arguments the script expects.E_WRONGARGS=65E_BADPID=66E_NOSUCHPROCESS=67E_NOPERMISSION=68PROCFILE=exeif [ $# -ne $ARGNO ]then  echo "Usage: `basename $0` PID-number" >&2  # Error message >stderr.  exit $E_WRONGARGSfi  pidno=$( ps ax | grep $1 | awk '{ print $1 }' | grep $1 )# Checks for pid in "ps" listing, field #1.# Then makes sure it is the actual process, not the process invoked by this script.# The last "grep $1" filters out this possibility.## pidno=$( ps ax | awk '{ print $1 }' | grep $1 )# also works, as Teemu Huovila, points out.if [ -z "$pidno" ]  #  If, after all the filtering, the result is a zero-length string,then #+ no running process corresponds to the pid given.  echo "No such process running."   exit $E_NOSUCHPROCESSfi  # Alternatively:#   if ! ps $1 > /dev/null 2>&1#   then # no running process corresponds to the pid given.# echo "No such process running." # exit $E_NOSUCHPROCESS# fi# To simplify the entire process, use "pidof".if [ ! -r "/proc/$1/$PROCFILE" ]  # Check for read permission.then  echo "Process $1 running, but..."   echo "Can't get read permission on /proc/$1/$PROCFILE."   exit $E_NOPERMISSION  # Ordinary user can't access some files in /proc.fi  # The last two tests may be replaced by:# if ! kill -0 $1 > /dev/null 2>&1 # '0' is not a signal, but  # this will test whether it is possible  # to send a signal to the process.# then echo "PID doesn't exist or you're not its owner" >&2# exit $E_BADPID# fiexe_file=$( ls -l /proc/$1 | grep "exe" | awk '{ print $11 }' )# Or   exe_file=$( ls -l /proc/$1/exe | awk '{print $11}' )##  /proc/pid-number/exe is a symbolic link#+ to the complete path name of the invoking process.if [ -e "$exe_file" ]  #  If /proc/pid-number/exe exists,then   #+ then the corresponding process exists.  echo "Process #$1 invoked by $exe_file." else  echo "No such process running." fi  #  This elaborate script can *almost* be replaced by#   ps ax | grep $1 | awk '{ print $5 }'#  However, this will not work...#+ because the fifth field of 'ps' is argv[0] of the process,#+ not the executable file path.## However, either of the following would work.#   find /proc/$1/exe -printf '%l'#   lsof -aFn -p $1 -d txt | sed -ne 's/^n//p'# Additional commentary by Stephane Chazelas.exit 0

#!/bin/bash# connect-stat.sh#  Note that this script may need modification#+ to work with a wireless connection.PROCNAME=pppd # ppp daemonPROCFILENAME=status  # Where to look.NOTCONNECTED=85INTERVAL=2   # Update every 2 seconds.pidno=$( ps ax | grep -v "ps ax" | grep -v grep | grep $PROCNAME |awk '{ print $1 }' )# Finding the process number of 'pppd', the 'ppp daemon'.# Have to filter out the process lines generated by the search itself.##  However, as Oleg Philon points out,#+ this could have been considerably simplified by using "pidof".#  pidno=$( pidof $PROCNAME )##  Moral of the story:#+ When a command sequence gets too complex, look for a shortcut.if [ -z "$pidno" ]   # If no pid, then process is not running.then  echo "Not connected." # exit $NOTCONNECTEDelse  echo "Connected."; echofiwhile [ true ]   # Endless loop, script can be improved here.do  if [ ! -e "/proc/$pidno/$PROCFILENAME" ]  # While process running, then "status" file exists.  then echo "Disconnected." #   exit $NOTCONNECTED  finetstat -s | grep "packets received"  # Get some connect statistics.netstat -s | grep "packets delivered"   sleep $INTERVAL  echo; echodoneexit 0# As it stands, this script must be terminated with a Control-C.# Exercises:# ---------# Improve the script so it exits on a "q" keystroke.# Make the script more user-friendly in other ways.# Fix the script to work with wireless/DSL connections.