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What does // do ? string//string ??

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Top Forums Shell Programming and Scripting What does // do ? string//string ??
# 1  
Old 09-26-2007
What does // do ? string//string ??
Hi,

Real easy question here, I think, just really hard to google this one.

What does the // do?
What is happening below:
Code:
if [ "${stringone//$stringtwo}" = "$stringone" ]
then
echo " ... "
else
echo " ...."
stringone=${stringthree//stringtwo}
fi

Thanks again people!
Last edited by rorey_breaker; 09-26-2007 at 07:11 AM..
# 2  
Old 09-26-2007
From the man page of bash:
Quote:
${parameter//pattern/string}
The pattern is expanded to produce a pattern just as in
pathname expansion. Parameter is expanded and the
longest match of pattern against its value is replaced
with string. In the first form, only the first match
is replaced. The second form causes all matches of
pattern to be replaced with string. If pattern begins
with #, it must match at the beginning of the expanded
value of parameter. If pattern begins with %, it must
match at the end of the expanded value of parameter.
If string is null, matches of pattern are deleted and
the / following pattern may be omitted. If parameter
is @ or *, the substitution operation is applied to
each positional parameter in turn, and the expansion is
the resultant list. If parameter is an array variable
subscripted with @ or *, the substitution operation is
applied to each member of the array in turn, and the
expansion is the resultant list.
I didn't get what this means though... trying to figure that out.

-edit

Ah, got it. This checks if the 'pattern' after being expanded in the same way as pathname expansion, is a substring of 'parameter'. If it is, you can replace it with 'string'. In your case, 'string' doesn't exist, so it will be replaced with nothing. If 'pattern' isn't a substring of 'parameter', then no just 'parameter' is the result. So what the if conditional is checking is whether stringtwo is a substring of stringone. If it is, the resultant expansion will not match with stringone.
Last edited by blowtorch; 09-26-2007 at 07:41 AM..
# 3  
Old 09-26-2007
Thanks very much.
Last edited by rorey_breaker; 10-23-2007 at 04:37 PM..
# 4  
Old 09-27-2007
Post the code once you're done. Most people here would get a kick out of playing it.
# 5  
Old 10-01-2007
Thank you.
12345678910
hangman.txt (3.7 KB) 
Last edited by rorey_breaker; 10-19-2007 at 05:37 AM..
# 6  
Old 10-01-2007
Quote:
Originally Posted by rorey_breaker
Thanks very much, I am trying to write hangman in bash. And attemping to use the // to see if the player guess is in the secret word.

Use a case statement:
Code:
read -n1 letter
case $word in
 *"$letter"* ) echo YES ;;
 *) echo NO ;;
esac

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