using awk in a bash script with if

Hi,

I'm doing a script in which I need to test a string and based on its result I'll decide if I go further or not.

The command below works fine (if the string starts with "Clean" it will print 1, otherwise 0).

echo | awk ' {print index("'"${task}"'", "Clean")}'

What I'm trying to do is to use the AWK with IF in a BASH script. Based on this post I did the following:

idx=$(awk '{print index("'"${task}"'", "Clean")}')
echo $idx
if [ "$idx" == "0" ]; then
   echo hello
fi

As I said, when I run the script it prints "0", but the second "echo" doesn't print anything, and of course the if doesn't works either.

Can anyone help me?

TIA,

Bob

From serverfault Bob Rivers

• Awk is the wrong solution here. How about:

  if [[ "$task" =~ ^Clean ]]; then
    echo hello
  fi
  

  There's also a sneaky substitution method:

  if [ "${task/#Clean/}" != "$task" ]; then
    echo hello
  fi
  

  But I find that to be far less readable.

  ---

  Chris reckons case is tidier... let's try that out:

  case $task in
    Clean*)
      echo hello
      ;;
  esac
  

  My aesthetic sense says "hell no with bells on", and fiddling with the formatting (Clean*) echo hello;; or similar) won't help much, IMAO. If you want a conditional, use an if, I say.

  chris : You can use case for stuff like this; it's typically quite a bit tidier.

  chris : The nice thing about case statements is that they eliminate great big piles of if ; then ; elif ; then ; elif ; then ; else; fi structures, and they have better regular expression matching than test.

  womble : Well, when we get to having lots of if/elif blocks *involving the same variable*, we can switch to using a case statement. Also, case uses pathname expansion (roughly, globbing), whereas `[[ =~` uses *actual* regular expressions.
  From womble

• Womble's answer is probably what I would go for, but you can also use grep:

  if echo cleanarf | grep -qi '^clean'; then 
     echo foo
  fi
  

  Drop the i switch to grep if you want it case sensitive (or if you do not want it case insensitive :-p ).

  womble : This is less readable, IMAO, and slower because it involves spawning a separate process.

  Kyle Brandt : Agreed, that is why I said I would opt for your answer :-P But options are good.
  From Kyle Brandt

• In your first example, you use echo to provide awk with a file (stdin), but in your script, there is no file for awk to process and it "hangs" waiting for input. You could use echo in your variable assignment in the $(), but I prefer to use /dev/null for this purpose (i.e. when there's no actual file to process).

  In order to avoid awkward quoting, you can use variable passing with the -v option to provide Bash variables to an awk script.

  You should find that this works:

  idx=$(awk -v task="$task" '{print index(task, "Clean")}' /dev/null)
  echo $idx
  if [ "$idx" == "0" ]; then
     echo hello
  fi
  

  You should probably use womble's suggestion, though, since it doesn't require spawning a separate process.

  From Dennis Williamson