Replace all letters in a word with '*' after a certain word in a text file

Question

I need to create a script that replaces all letters of a word after a certain word with an asterisk (*).  For example:

sed 's/Word:[^ ]\+/Word:*/' Desktop/script_test

But this script replaces the entire word with only one asterisk, while I want to replace all letters. How can I do that? For example, with this input:

Word: cat

I want to get

Word: ***

I am running Linux.

P.S. The input must be read from a text file and also saved to the same file.

Answer 1

You could do it one at a time in a loop:

sed -e :1 -e 's/\(Word: *[^ ]*\)[^ *]/\1*/;t1'

To edit the file in place and assuming all the characters to replace are single-byte, you can make both sed's stdin and stdout the file as in:

sed ... < file 1<> file

Or with GNU sed, use the -i flag as in:

sed -i ... file

(Though that will replace the file with a new one (though with the same name). With BSD sed, use -i '' instead of -i).

Answer 2

How about:

$ cat file
Word: cat
Word: foobar
$ sed -E 's/Word: *//; s/./*/g; s/^/Word: /' file
Word: ***
Word: ******

To modify the file in place, just use -i:

$ sed -E -i 's/Word: *//; s/./*/g; s/^/Word: /' file

Note that this won't work if Word: is not the first word of the line. If that's a problem, you can use this instead:

perl -pe 's/Word:\s*\K(\S+)/sprintf "*" x length($1)/e' file

That, in turn, assumes that you want the first Word: on each line and also that you want everything following it to be replaced by *. If you only want the first word after Word: to be replaced, you really should ask a new question or, at least, clarify this one.

Answer 3

You could to this using sed as follows:

echo 'Word: cat' |
sed -e '
   s/Word:/&\n/
   :loop
      s/\n\([^a-zA-Z]*\)[a-zA-Z]/\1*\n/
   tloop
   s/\n\([^a-zA-Z]*\)$/\1/
' 

Answer 4

You could use this time employing the hold space for manipulations, as:

sed -e '
   s/Word:/&\n/   # everything to the right of marker is asterisk zone
   h              # will need later on for reconstructing, so save orig
   s/.*\n//       # retain only the asterisk zone
   s/[a-zA-Z]/*/g # perform the asterisk operation
   H;g            # abut onto original data
   s/\n.*\n//     # peel off unwanted data
'

Answer 5

Perl

echo 'Word: cat' |
perl -lpe '
   1 while s/(?<=Word:)([^a-zA-Z]*)([a-zA-Z]+)/$1 . "*" x length($2)/e;
'

Bash

eval "`echo 'NL=qsq' | tr 'qs' '\047\012'`"; # newline
echo 'Word: cat' |
while IFS= read -r line
do
   var=${line/Word:/Word:"$NL"}
   var1=${var#*"$NL"}     var2=${var%"$NL"*}
   var3=${var1//[a-zA-Z]/*}
   var4=${var2}${var3}
   printf '%s\n' "$line" "$var4"
done

Answer 6

Python solution with more flexible command-line arguments:

#!/usr/bin/env python3
import sys, fileinput

def replace_after(haystack, needle, replacement):
    pos = haystack.find(needle)
    if pos >= 0:
        pos += len(needle)
        return haystack[:pos] + (replacement * (len(haystack) - pos))
    else:
        return haystack

if __name__ == '__main__':
    needle, replacement = sys.argv[1:3]
    del sys.argv[1:3]

    with fileinput.input() as finput:
        for line in finput:
            print(replace_after(line.rstrip('\n'), needle, replacement))

Usage:

python3 unix.se.346510.py <NEEDLE> <REPLACEMENT> [FILES...]

Example:

$ printf '%s\n' 'Word: foo' 'more Word: bar-baz' | python3 unix.se.346510.py 'Word: ' '*'
Word: ***
more Word: *******

Answer 7

An awk solution and a shell solution:

echo '"Hello: World"' | awk '{ gsub("[^\"]", "*", $2); print }'

We have to escape the " in [^\"] since the regular expression itself is in double quotes. This generates

"Hello: *****"

With the shell (at least bash and ksh93):

echo '"Hello: World"' | {
  read -r prefix rest
  printf '%s %s\n' "$prefix" "${rest//[^\"]/*}"
}

Assuming the text "Hello: World" is on a line of its own, but embedded in a larger text in the file greetings.txt:

awk '/"Hello: [^"]*"/ { gsub("[^\"]", "*", $2) } { print }' greetings.txt >greet.tmp && mv greet.tmp greeting.txt

or (again, with bash or ksh93),

while read -r prefix rest; do
    if [[ "$prefix" =~ ^\"Hello: ]]; then
        rest=${rest//[^\"]/*}
    fi
    printf '%s %s\n' "$prefix" "$rest"
done <greetings.txt >greet.tmp
mv greet.tmp greetings.txt

For the input

Specific recipients:
"Hello: Mom!"
"Hello: Cat!"

General recipients:
"Hello: World!"

these two solutions generate

Specific recipients:
"Hello: ****"
"Hello: ****"

General recipients:
"Hello: ******"

Answer 8

Stuff like this goes better with flex:

%option 8bit main
%s star
%%
Word:           ECHO;  BEGIN star;
<star>[^ \t\n]+ memset(yytext,'*',yyleng); ECHO; BEGIN 0;

put that in say star.l, then make star.

(edit: states are vast overkill for this. better:

%option 8bit main
%%
Word:[^ \t\n]* memset(yytext+5,'*',yyleng-5); ECHO;

)

Answer 9

Using awk, you don't mention, specific use of sed :)

echo "Word: cat" | awk '{printf $1" "; for (i=1;i<=length($2);i++) printf "*"}'

Result:

Word: ***