Find string while knowing part of it and return string

If your grep supports perl compatible regular expressions, you could match non-greedily up to the next word boundary:

echo "$string" | grep -oP 'Icecream.*?\b'

Otherwise, match the longest sequence of non-blank characters:

echo "$string" | grep -o 'Icecream[^[:blank:]]*'

Or keep everything in the shell and remove the longest trailing sequence of characters starting with a space:

echo "${string%% *}"

Since you tagged bash:

[[ $string =~ (Icecream[^ ]*) ]] && result=${BASH_REMATCH[1]}

More generally, for a search term in $search:

[[ $string =~ ($search[^ ]*) ]] && result=${BASH_REMATCH[1]}

... or with parameter expansion:

# remove any leading text up to -and through- the search text:
x=${string##*$search}

# remove any trailing space onwards
result=$search${x%% *}

Using a grep that knows about -o:

$ printf '%s\n' "$string" | grep -o '\<Icecream[^[:blank:]]*'
Icecream123

The pattern \<Icecream[^[:blank:]]* matches the string Icecream (where the I is preceded by a non-word character, or the start of the line) followed by zero or more non-blanks (not spaces or tabs).

---

Using awk:

$ printf '%s\n' "$string" | awk -v RS=' ' '/^Icecream/'       
Icecream123

The awk program divides the string into space-separated records, and tests each one. It will print the ones that start with the string Icecream.

Using mawk or GNU awk, you may also use

printf '%s\n' "$string" | awk -v RS='[[:blank:]]' '/^Icecream/'

since they interpet RS as a regular expression if it contains more than one character.

---

With sed, in a similar fashion as with grep:

$ printf '%s\n' "$string" | sed 's/.*\(\<Icecream[^[:blank:]]*\).*/\1/'
Icecream123

---

Using /bin/sh:

set -- Icecream123 AirplaneBCD CompanyTL1 ComputerYU1
for string; do
    case $string in
        Icecream*)
            printf '%s\n' "$string"
            break
    esac
done

---

Perl (with a little help from tr):

$ printf '%s\n' "$string" | tr ' ' '\n' | perl -ne '/Icecream\S*/ && print'
Icecream123

or just

$ printf '%s\n' "$string" | perl -ne '/(Icecream\S*)/ && print $1, "\n"'
Icecream123