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ksh String Manipulation - removing variables from within a variable


 
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# 1  
Old 01-31-2019
ksh String Manipulation - removing variables from within a variable

Hi. I'd like to remove all values in a string variable that also exist in a second variable. What is the appropriate approach to take here? I can use a 'For' loop and check each element and then populate a new string. But is there a cleaner, simpler way?

E.g. I have the following 2 variables
Code:
NAMES="John Paul George Ringo"
EXCLUDE_NAME="Ringo"

What would be the simplest way to update $NAMES so that all $EXCLUDE_NAME members have been removed?
This works but there must be better way:

Code:
for X in ${NAMES} ; do
    if [[ ! "$EXCLUDE_NAME" =~ "$X" ]]; then
       NEW_NAMES="$NEW_NAMES $X"
    fi
done


Many thanks
# 2  
Old 01-31-2019
Simple form using bash without utilities.
Longhand OSX 10.14.1, default bash terminal.
Code:
Last login: Thu Jan 31 18:23:42 on ttys000
AMIGA:amiga~> NAMES=( John Paul George Ringo )
AMIGA:amiga~> EXCLUDE_NAME='Ringo'
AMIGA:amiga~> STRING=""
AMIGA:amiga~> for (( N=0; N<${#NAMES[$@]}; N++ ));do if [ "${NAMES[$N]}" != "${EXCLUDE_NAME}" ]; then STRING="${STRING} ${NAMES[$N]}"; fi; done
AMIGA:amiga~> echo ${STRING}
John Paul George
AMIGA:amiga~> _

Have fun...
# 3  
Old 01-31-2019
You need to post the ksh version that you use. ksh93 has "Parameter Expansion". man ksh:
Quote:
${parameter/pattern/string}
...
Expands parameter and replaces the longest match of pattern with the given string.
In your case:

Code:
echo ${NAMES//$EXCLUDE_NAME}
 John Paul George

In case $EXCLUDE_NAME contains several space separated strings, you'd need to run a loop across all these strings.
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# 4  
Old 01-31-2019
Quote:
Originally Posted by RudiC
You need to post the ksh version that you use. ksh93 has "Parameter Expansion".
Your solution is not only correct - it is so even to the extent that this will work in ksh88 too. In terms of parameter expansion ksh88 and ksh93 are very much identical.

Of course, in ksh88 you would have to write:
Code:
NAMES="Mick Keith Ron Bill Charlie"
EXCLUDE_NAME="Bill"
echo "${NAMES/${EXCLUDE_NAME}/}"

instead to arrive at Mick Keith Ron Charlie. And beware of the -satisfaction option....

bakunin

Last edited by bakunin; 02-01-2019 at 08:14 AM.. Reason: corrected a typo
This User Gave Thanks to bakunin For This Post:
# 5  
Old 01-31-2019
Hi RudiC & bakunin...

I learn something new every day.
That expansion, new to me, works in bash too.
(Sadly it is not POSIX compliant though.)


Super stuff.
Thanks a mil'.


Bazza.
# 6  
Old 01-31-2019
@bakunin: I can't get no ... oh!


Parameter expansion gets to combine array expansion with the substitution expansions in both bash and ksh93:
Code:
$ namea=( John Paul George Ringo )
$ exclude=Ringo
$ echo ${namea[@]//$exclude/}
John Paul George

but notice this difference between the two shells:
bash:
Code:
$ nameb=( ${namea[@]//$exclude/} )
$ echo ${#nameb[@]}
3

ksh93:
Code:
$ nameb=( ${namea[@]//$exclude/} )
$ echo ${#nameb[@]}
4

so in bash you could use this method to delete an item from an array but in ksh93 it will simply empty the item.


Andrew
# 7  
Old 02-01-2019
Still, this is string substitution.
// is global substitution (retry if successful)
/ is one substitution
Only ksh93 has it correctly implemented (and bash-4, while bash-2 and bash-3 have a little bug in it).
For example, Solaris ksh88:
Code:
echo "${NAMES//${EXCLUDE_NAME}}"
ksh: "${NAMES//${EXCLUDE_NAME}}": bad substitution


Last edited by MadeInGermany; 02-01-2019 at 06:16 AM..
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