Shell Programming and Scripting

Hi All,

Below is a sample command that I can run without any problem in the command line.

Command Line
But once I put that command line in file (list.txt) and read from it, an error occurs. Pls. see below the code:


The list.txt contains the line below:
Need help badly to resolve this issue. Thanks in advance.

You will have to change the script file. BTW this is a less than useful way to run scripts because it negatively impacts performance. And prevents the use of variables defined in the input text file.

every "command " you read in you have to preface with

Code:

eval

Please consider reading about it before you cause more problems for yourself.

example:

Code:

while read cm
do
   eval "cmd"
done < input_file.txt

Note that when you do that you cannot have a variable set up in line 1 of input_file.txt
and then read the next line and use that variable. This is because each eval "line of text" runs in a separate child process. No variables are preserved in the current process. Each line is a separate world of its own.

Thanks Jim....

Just to share to everyone the updated code using eval:

Code:

cat ./list.txt|while read xLine
do
cmd=`echo $xLine | awk -F "|" '{print $2}'`
echo "========="
eval "$cmd"
done

That is a useless use of cat and will prevent variables set inside the loop from being used outside the loop.

There is also no point using awk to split variables here when read can do that by itself.

There's also no point using awk 10,000 times to process 10,000 lines when awk can do that all at once. It's like making a hundred phonecalls to say a hundred individual words.

This should do the job with less fuss:

Code:

while IFS="|" read -r A B C D E
do
        echo "========="
        eval "$B"
done < inputfile

p.s.: The -r is probably necessary either way to read shell code. Without it, code containing backslash characters may be mangled.