How can I replace all middle characters with '*'? - awk

Question

I would like to replace middle of word with ****.
For example :
ifbewofiwfib
wofhwifwbif
iwjfhwi
owfhewifewifewiwei
fejnwfu
fehiw
wfebnueiwbfiefi
Should become :
if********ib
wo*******if
iw***wi
ow**************ei
fe***fu
fe*iw
wf***********fi
So far I managed to replace all but the first 2 chars with:
sed -e 's/./*/g3'
Or do it the long way:
grep -o '^..' file > start
cat file | sed 's:^..\(.*\)..$:\1:' | awk -F. '{for (i=1;i<=length($1);i++) a=a"*";$1=a;a=""}1' > stars
grep -o '..$' file > end
paste -d "" start stars > temp
paste -d "" temp end > final

Answer 1

I would use Awk for this, if you have a GNU Awk to set the field separator to an empty string (How to set the field separator to an empty string?).
This way, you can loop through the chars and replace the desired ones with "*". In this case, replace from the 3rd to the 3rd last:
$ awk 'BEGIN{FS=OFS=""}{for (i=3; i<=NF-2; i++) $i="*"} 1' file
if********ib
wo*******if
iw***wi
ow**************ei
fe***fu
fe*iw
wf***********fi

Answer 2

If perl is okay:
$ perl -pe 's/..\K.*(?=..)/"*" x length($&)/e' ip.txt
if********ib
wo*******if
iw***wi
ow**************ei
fe***fu
fe*iw
wf***********fi
..\K.*(?=..) to match characters other than first/last two characters
See regex lookarounds section for details
e modifier allows to use Perl code in replacement section
"*" x length($&) use length function and string repetition operator to get desired replacement string

Answer 3

You can do it with a repetitive substitution, e.g.:
sed -E ':a; s/^(..)([*]*)[^*](.*..)$/\1\2*\3/; ta'
Explanation
This works by repeating the substitution until no change happens, that is what the :a; ...; ta bit does. The substitution consists of 3 matched groups and a non-asterisk character:
(..) the start of the string.
([*]*) any already replaced characters.
[^*] the character to be replaced next.
(.*..) any remaining characters to replace and the end of the string.
Alternative GNU sed answer
You could also do this by using the hold space which might be simpler to read, e.g.:
h # save a copy to hold space
s/./*/g3 # replace all but 2 by *
G # append hold space to pattern space
s/^(..)([*]*)..\n.*(..)$/\1\2\3/ # reformat pattern space
Run it like this:
sed -Ef parse.sed input.txt
Output in both cases
if********ib
wo*******if
iw***wi
ow**************ei
fe***fu
fe*iw
wf***********fi

Answer 4

Following awk may help you on same. It should work in any kind of awk versions.
awk '{len=length($0);for(i=3;i<=(len-2);i++){val=val "*"};print substr($0,1,2) val substr($0,len-1);val=""}' Input_file
Adding a non-one liner form of solution too now.
awk '
{
len=length($0);
for(i=3;i<=(len-2);i++){
val=val "*"};
print substr($0,1,2) val substr($0,len-1);
val=""
}
' Input_file
Explanation: Adding explanation now for above code too.
awk '
{
len=length($0); ##Creating variable named len whose value is length of current line.
for(i=3;i<=(len-2);i++){ ##Starting for loop which starts from i=3 too till len-2 value and doing following:
val=val "*"}; ##Creating a variable val whose value is concatenating the value of it within itself.
print substr($0,1,2) val substr($0,len-1);##Printing substring first 2 chars and variable val and then last 2 chars of the current line.
val="" ##Nullifying the variable val here, so that old values should be nullified for this variable.
}
' Input_file ##Mentioning the Input_file name here.