Verbose output of shell script

Question

You don't say what sort of shell you're running. If you're using sh/bash, try

sh -x script_name

to run your script in a verbose/debug mode. This will dump out all the commands you execute, variable values etc. You don't want to do this normally since it'll provide a ton of output, but it's useful to work out what's going on.

As noted in the comments, you can add this flag to your #!/bin/bash invocation in your script.

an easy way:

for i in -20 -19 -18 -17 -16 -15 -14 ... 18 19
do
  echo "Nice value is $i"
  echo "nice -n $i ./app1"
  nice -n $i ./app1
done

These will demonstrate 'eval' and 'set' to do what you want:

::::::::::::::
a.sh
::::::::::::::
#!/bin/sh

clear

i=-20
while [ ${i} -lt 20 ]; do
  echo "Nice value is $i"
  cmd="nice -n $i ./app1"
  echo ${cmd}
  eval ${cmd}
  i=`expr ${i} + 1`
done

::::::::::::::
b.sh
::::::::::::::
#!/bin/sh

clear

i=-20
while [ ${i} -lt 20 ]; do
  echo "Nice value is $i"
  set -x
  nice -n $i ./app1
  set +x
  i=`expr ${i} + 1`
done