Shell Programming and Scripting

One of the monitoring tools in Java is called `jps`, and it monitors all Java processes that are run by the user, an example output would be like this:

3459 Jps
2348 test
2311 Util

where the first column represents Process IDs and the second column represents Java processes names. Therefore, if I wanted to find the process ID for some Java process, say test, I could type `jps | grep test` and then take the first argument in the line, which would be the process ID.

Now I had an idea to do it in a simpler way (rather than just writing a C or Java program), I could write a simple sh script that goes like this (call it tokenizer)

Code:

#!bin/sh
echo $1

and by typing `chmod +x tokenizer` and then: `jps | grep test | tokenizer` I would think I should get 2348 as an output to the shell, which is the PID for `test` Java process, but that did not happen. Anybody know why?

This is because the script you have written does one hing only, it prins out the first command line argument passwd to it.

A better way to do this would be to put the processing inside the script.

for example:

Code:

#!/bin/ksh
# jpsearch.ksh
#
jps | awk "/$1/{print \$1}"

note you will need to give the full path to jps for this to sure to work.

then you would just chmod +x the file: and run it as
./jpsearch test

Thanks for the solution, isn't the piping supposed to pass a line from grep as command line arguments for the script?

No, the output from the pipe is redirected to stdin for the command after the pipe. The comand line arguments are read when the program is executed,before stdin is opened.

Still, it is possible to do in a shellscript what neked wants. The task is to read any line of input, "tokenize" (split it at word boundaries) it and put it to <stdout>. The following should do the trick:

Code:

#!/bin/ksh

line=""
word=""
while read line ; do
     while [ -n "$line" ] ; do
          print - "$line" | read word, line
          print - "$word"
     done
done

bakunin

You would need a little bit more logic in there to provide answer to the original problem. You would need to test see if it was the correct name of the process being searched for before printing $word

Not really, as this was only intended to replace the original "tokenizer.sh" from nekeds first post, where he suggested a sole "echo $1" to do the tokenizing. He confused <stdin> and the commandline there an i wanted to show him how to implement his original idea correctly. I do NOT think that this "tokenizing" is useful or a recommendable approach though.

bakunin