Reading UNIX commands from file and redirecting output to a file

Shell Programming and Scripting
1

Hi All

I have written the following script:

#!/bin/ksh
while read cmdline
do 
  echo `$cmdline`
  pid="$cmdline"
done<commands.txt

===========
commands.txt contains:

ps -ef | grep abc | grep xyz |awk '{print $2};

My objective is to store the o/p of the command in a variable and do ceratin operations on it. It works fine if i just ls but not working with pipe...

2

If your snipit of code is cut directly from your file you are missing a quote

ps -ef | grep abc | grep xyz |awk '{print $2};'

If it was just a cut/paste error in your quote, this might also be a better way:

evail pid=\$( $cmdline )

The eval causes the contents of $cmdline to be expanded, and then the statement is executed which causes the command inside $( ... ) to be executed the the resulting output assigned to pid.

Hope this gets you moving in the right direction.

3

I tried bt its giving syntax error that '(' is expected i the line:

eval pid= \$( $cmdline )
4

Space between the equal and backslant is the problem I think:

eval pid=\$( $cmdline )

There cannot be spaces before or after the equal sign in bash or ksh.

5

u cn just write: pid=eval "$cmdline" and it will work fine....

Thanks for giving the idea of eval... Its wrking fine nw

6

I'm curious why you don't just set the script executable and ./script > file ?

7

Actually i need to use the output in some other script as well as i m getting this input by running other script... :slight_smile:

8

If the operations are limited within the loop, you could just skip the "commands.txt" stuff.

ps -ef | grep abc | grep xyz |awk '{print $2} | while read pid
do 
  echo $pid
done

You might need to handle the variable scoping (subshell) if needed outside the loop.

9

eval "$cmdline" works.

Why there is need of special syntax eval pid=\?($cmdline)