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2005/06/05 How does a shell script know how it was invoked?


© June 2005 Tony Lawrence

Sometimes you want a shell script to have different behavior depending upon how it was invoked. One trick I've used in that situation is to walk the process tree backwards and see what invoked the script. You can do that using ps or by looking in /proc. PPID is probably in your environment already, so it can be as simple as

ps -p $PPID -o cmd

or

ps -p $PPID -o comm 
 

Of course that may not be far enough up the tree to find out whatever it is you need to know. For example, see How do I find out who or what halted my system (Old Sco Unix)?.

In some cases, it's not so much what invoked the script as what it is running under: is it reading from a pipe, for example. The "tty" command can tell you that:

$ cat t.sh
tty || exit 1
echo "OK"
$ ./t.sh
/dev/pts/0
OK
$ date | ./t.sh
not a tty
 

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Sun Jun 5 06:17:34 2005: 614   anonymous


You can also use this:

 
if [ -t 0 ] 
then 
    echo "Reading from a terminal!" 
fi 
if [ -t 1 ] 
then 
    echo "Writing to a terminal! 
fi 


Arvind

PS: Why does "pre" tag not work very well here?



Sun Jun 5 09:52:24 2005: 615   TonyLawrence

gravatar
PRE doesn't work well simply because I haven't taken the time to fix the code.




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