Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
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\n'
# lsof −aFn −p $1 −d txt | sed −ne 's/^n//p'
# Additional commentary by Stephane Chazelas.
exit 0
Example 28−2. On−line connect status
#!/bin/bash
PROCNAME=pppd # ppp daemon
PROCFILENAME=status # Where to look.
NOTCONNECTED=65
INTERVAL=2
# Update every 2 seconds.
pidno=$( 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 $NOTCONNECTED
else
echo "Connected."; echo
fi
while [ true ]
do
# Endless loop, script can be improved here.
if [ ! −e "/proc/$pidno/$PROCFILENAME" ]
# While process running, then "status" file exists.
then
echo "Disconnected."
exit $NOTCONNECTED
fi
Chapter 28. /dev and /proc 314