Shell Programming and Scripting

Please become accustomed to provide decent context info of your problem.

It is always helpful to carefully and detailedly phrase a request, and to support it with system info like OS and shell, related environment (variables, options), preferred tools, adequate (representative) sample input and desired output data and the logics connecting the two including your own attempts at a solution, and, if existent, system (error) messages verbatim, to avoid ambiguities and keep people from guessing.

man bash:
What do you think is the output of

Code:

course=`nzsql -host -d db -Atc "select course from table group by 1 order by 1;"`

?

I have no idea how you arrived at this, but if this would work, shell programming woud be a bad idea. ;-)

First: forget about backticks. They are just there for backwards compatibility with a shell which is not in use any more since about 25 years. Just forget they exist.

Second: even if you use backticks, x=`some -command` is a variable assignment. In fact it does: run the command some -command and assign its output to variable x. So, what you did amounts to:

Code:

while read line ; do
     command
done < x="blabla"

which is obviously not what you intended. You do it the same way i showed you with sed: by pipelining it like this:

Code:

command |\
while read line ; do
     other_command "$line"
done

The pipeline can have more than one part, so this would also be possible:

Code:

command1 |\
command2 |\
command3 |\
.... |\
while read line ; do
     other_command "$line"
done

This runs command1, then pours its output into command2, the output of command2 into command3 and so forth, until the output of the last command is poured into the loop, which reads it line by line and processes it.

I am sure you can now construct your own script with ease, no?

By the way: if you want to process lines like you do stay generally away from for-loops. While-loops are a lot more flexible when it comes to parsing input, even when word-splitting is involved.

Suppose you have a file (or process output, which is effectively the same) of this structure:

Code:

line1-word1 line1-word2 line1-word3
line2-word1 line2-word2 line2-word3
line3-word1 line3-word2 line3-word3
line4-word1 line4-word2 line4-word3

and you want to process the second word of every line ("line1-word2", "line2.word2", etc.) then this will do it:

Code:

InFile="/path/to/input"
secondword=""

while read junk secondword junk ; do
     echo "this is $word"
done <"$InFile"

Try it out. You could do that with some gymnastics and a for-loop too, but this is IMHO a lot easier to write and a lot easier to read and understand.

I hope this helps.

bakunin

Sure RudiC,will make a note of it.

---------- Post updated at 03:15 PM ---------- Previous update was at 03:13 PM ----------

Bakunin, Thanks a ton for your detailed explanation.I will try to construct my script now!

I am facing one more challenge here, for time being i have passed the variable from a file line by line and it is working fine but i have some 2k names in the file so i need to make checkpoint at 100 each time and then start executing the steps till end of the file. For example, my script should consider the first 100 names line by line,passing it as a parameter and execute the code. and the when i execute it next time it should skip the first 100 lines and pick it from 101 line till 200..

Thanks again!

There are umpteen possible approaches to your last question, e.g. using a counter in the loop, splitting the input file, using nested loops, mayhap a dedicated script.
Why don't you present your script and input data, and we'll discuss?