Shell Programming and Scripting

Hi,

my script is setting a variable with value and this variable is present in my another command that is coming from external file and this command is internally called after this variable is set. but while execution of this command, the value is not retrieved properly.

say,

my script has a variable PWD and it is set to some value say abcd

export PWD=abcd
echo $PWD #here it is returinng the value abcd perfectly.

in the same shell script i am using some piece of code which will bring the unix commands from a external file and execute it one by one. one of the commands is echo $PWD
while execution at this time, it is not returning the value abcd

echo $PWD
simply it is returning $PWD instead of abcd

what is the mistake i do not understand. Please suggest.

Aren't you placing "$PWD" between single quotes?

Code:

# echo '$PWD'
$PWD

I am not using single quotes.

I have also tried with double quotes. still it is not working as expected.
echo $PWD
echo "$PWD" #these two i tried. no luck.

external file has line as below

PRI#echo $PWD

from this i am getting only the exact command and storing it in a variable and executing it.

export command=`echo $line | cut -d '#' -f2,3,4'
$command

PS: i am able to execute other commands properly from this file. only commands which has some variables present are not working.

Here it works!

Code:

# line="PRI#echo $PWD"
# command=`echo "${line}" | cut -d '#' -f2,3,4`
# $command
/current/path

You can try to use: eval, but be careful, eval is evil!

Code:

# line="PRI#echo \$PWD"
# command=`echo "${line}" | cut -d '#' -f2,3,4`
# echo $command
echo $PWD
# eval $command
/current/path

eval is doing perfectly.
Thanks a lot for your help.

i never used eval before. why it is evil?

If you are using a "configuration" file to put commands you need to execute, be careful if somente puts a "rm -rf <some path>" on it on purpose! Or some "code injection"!

Check this blog with JScript posts about it:
-----> 1. Eval is Evil, Part One - Fabulous Adventures In Coding - Site Home - MSDN Blogs
-----> 2. Eval is Evil, Part Two - Fabulous Adventures In Coding - Site Home - MSDN Blogs

In general, eval is not a good practice, but in a controled environment, it is ok!

I hope it helps.

---------- Post updated at 13:33 ---------- Previous update was at 13:33 ----------

If you are using a "configuration" file to put commands you need to execute, be careful if somente puts a "rm -rf <some path>" on it on purpose! Or some "code injection"!

Check this blog with JScript posts about it:
-----> 1. Eval is Evil, Part One - Fabulous Adventures In Coding - Site Home - MSDN Blogs
-----> 2. Eval is Evil, Part Two - Fabulous Adventures In Coding - Site Home - MSDN Blogs

In general, eval is not a good practice, but in a controled environment, it is ok!

I hope it helps.