Shell environment debugging

Introduction

On unix systems one may need to know the various details of how a script is called (effective userid, command line arguments) or what environmental settings are available. The yak script can facilitate discovery of this information, by recording details of the command line arguments, environment, and standard input to a temporary file.

Examples

Example usage of the yak script.

LPRng Filter

The LPRng print server can run print jobs through filters. Many command line options are supplied, which yak can easily list to a file to assist with writing a proper print filter. Install yak locally, then add the following print queue definition to the printcap.

yak:
:client:mx=0:sh:lp=yak@%P
yak:
:server
:lp=/dev/null
:sd=/var/spool/lpd/%P
:if=/usr/local/bin/yak

Next, rebuild and restart LPRng, then send a test print job. Then investigate /tmp/yak.* for details on the environment.

# checkpc -f
Warning - changing ownership '/var/spool/lpd/yak' to 4/7
Warning - changing ownership '/var/spool/lpd/yak' to 4/7
# lpc reread all
# echo test | lpr -P yak
# cat /tmp/yak.*

Mac OS X StartupItems

To see what environment the Mac OS X StartupItems items are run in, install the YAK StartupItem into a StartupItems folder.

$ sudo tar xvzfC YAK.tar.gz /Library/StartupItems

Then, reboot the system, and look at the the /tmp/YAK.* file to see what the environment was like.

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