UNIX for Dummies Questions & Answers

#!/bin/sh
for x in A B C
do
echo "This is ${x}"
done

This is A
This is B
This is C

Ok, can someone help me out with this? I wrote this simple for loop. What I am trying to accomplish is the following:

For each of the letters in the for loop ( A B C ) I want to echo This is (letter). Simple enough. Next, when I am passing a parameter to this script, if the parameter that I am passing it equals any of the letters in my for loop, I want the loop to start from the parameter given and continue through the end of the loop. I was playing around with continue and break, but not sure if they will or will not accomplish what I want. Any ideas would be GREATLY appreciated .

Wanted Results:

IN COMMAND LINE: myscript.sh B
Script will get executed and the results would be:
This is C

IN COMMAND LINE: myscript.sh A
This is B
This is C

You get the picture, (hopefully). As always, Thanks!

What should happen if the letter is not one of those? Nothing?

Just keep a state variable.

Code:

seen=false
for x in A B C; do
  case $1 in $x) seen=true; continue;; esac
  $seen || continue
  echo This is $x
done

The construct m || n reads out "m or n" and basically means if m is false, execute n; in other words, it's a convenient shorthand for "if ! m; then n; fi"

false and true are shell commands which simply set their exit code to a false (non-zero) and true (zero) value, respectively. (The convention in the shell is that a zero exit code signifies success, and anything else, failure.)

era, you have gotten me out of some tight spots, my friend. Thank you so much for your quick and helpful responses.

P.S. If the letter given as a parameter is not present in the for loop, nothing shall happen. At least I don't think it does. Hmm, let me do more analysis. Either way, thanks a bunch!