ash test: is string A contained in string B

chochem · 09-23-2008, 06:28 AM

I'm trying to port a bash script to a busybox setup. Since busybox uses ASH rather than BASH, some things don't work. IN particular:

Code:

[[ "ab bc de" =~ "ab" ]]

tests if ab is contained within "ab bc de" in Bash. I'm stumped as to how to do something similar in Ash (if at all possible). Any suggestions?

keefaz · 09-23-2008, 07:24 AM

You could use grep like: if echo "ab bc de" | grep "ab"; then...

pixellany · 09-23-2008, 07:25 AM

I'll bite---what is ASH? Does it have a manual?

Quote:

Since busybox uses ASH rather than BASH

Why?

chochem · 09-23-2008, 07:50 AM

D'oh, grep... Yeah that should do it, although I'm trying to avoid calling too many outside programs (the computing power on this thing is laughable).

pixellany: http://en.wikipedia.org/wiki/Ash_shell

radoulov · 09-23-2008, 08:31 AM

Quote:

Originally Posted by chochem

D'oh, grep... Yeah that should do it, although I'm trying to avoid calling too many outside programs (the computing power on this thing is laughable).[...]

Use case:

Code:

case $string in
  *ab*) return 0 ;;
     *) return 1 ;;
esac

chochem · 09-23-2008, 09:21 AM

Quote:

Originally Posted by radoulov

Code:

case $string in
  *ab*) return 0 ;;
     *) return 1 ;;
esac

Very impressive - I'd nver have thought of that. Thanks, radulov

archtoad6 · 09-24-2008, 06:59 AM

I wonder if the spaces in your string ("ab bc de"), I will call it "S", indicate that you are mentally dividing it into words & assuming that your pattern (P="ab") is being tested for as a word? All the solutions discussed so far will give a positive when S="abbcde" or S="zab bc de". Is this what you intend?

The bash & grep solutions can narrow the match by using the regex word boundary symbol "\b" (see the grep man page):

Code:

[[ "$S" =~ "\b$P\b" ]]
echo "$S"  | grep "\b$P\b"

,
but the case method (brilliant suggestion, BTW) needs a more complicated solution:

Code:

case $S in
  "$P "*|*" $P "*|*" $P")   return 0 ;;
                       *)   return 1 ;;
esac

(Forgive the double pun -- I couldn't resist) It's a case of considering the corner cases.

It may well be that your actual string is very well structured & you don't need to consider this.
HTH someone.