How to not interpret string as command

Question

I'm writing a script which should copy a client system and change some lines in a file.

There is a source file which has a line like:

$DB_HOST = "LegitDbHost";

And the destination file has a line like:

$DB_HOST = "testDbHost";

So i need to replace the destination line with the source line and I want to print out something like this:

Replacing line 12: '$DB_HOST = "testDbHost";' ==with==> '$DB_HOST = "LegitDbHost";'(y/n): 

So far i got this:

toReplace='$DB_HOST';
sourceLine=$(cat ./sourceFile.php | grep -m 1 "$toReplace[[:space:],=]");
destLineNr=$(cat ./destFile.php | grep -n -m 1 "$toReplace[[:space:],=]" | grep -Eo '^[^:]+');
destLine=$(cat ./destFile.php | grep -m 1 "$toReplace[[:space:],=]");
read -p "Replacing line $destLineNr: $destLine ==with==> $sourceLine.(y/n): ";

however, my output looks like this:

==with==> $DB_HOST    ST   = "testDbHost";.(y/n): 

I think it's because the sourceLine has a ; inside and that gets interpreted as a command end. I just don't know how to get around that.

I hope it's understandable.

Edit: as suggested i tried using echo -n

toReplace='$DB_HOST';
sourceLine=$(cat ./sourceFile.php | grep -m 1 "$toReplace[[:space:],=]");
destLineNr=$(cat ./destFile.php | grep -n -m 1 "$toReplace[[:space:],=]" | grep -Eo '^[^:]+');
destLine=$(cat ./destFile.php | grep -m 1 "$toReplace[[:space:],=]");
echo -n "Replacing line $destLineNr: "
echo -n $destLine
echo -n " ===with===> "
echo -n $sourceLine

this prints out:

===with===> $DB_HOST = "testDbHost";OS";

Answer 1

Try:

#! /bin/zsh -
die() {
  print -ru2 -- "$@"
  exit 1
}
srcFile=./sourceFile.php
dstFile=./destFile.php
toReplace='$DB_HOST'
sourceLine=$(<"$srcFile" grep -Pm1 "\Q$toReplace\E[\s,=]") ||
  die "Can't find $toReplace in $srcFile"
<"$dstFile" grep -nPm 1 "\Q$toReplace\W[\s,=]" |
  IFS=: read -r destLineNr destLine ||
  die "Can't find $toReplace in $dstFile"
if
  read -q "?Replacing line $destLineNr: ${(q+)destLine} ==with==> ${(q+)sourceLine}? (y/n): "
then
  (
     export destLineNr destLine
     perl -lpi -e '$_ = $ENV{destLine} if $. == $ENV{destLineNr}' -- "$dstFile"
  )
fi

Using ${(q+)line} zsh parameter expansion, will make sure CR characters in that variable (as it looks like your input files have MSDOS CRLF delimiters instead of Unix LF ones) is rendered as C-M instead of being sent as-is to the terminal (for a terminal, a CR character makes the cursor go back to the beginning of the line (makes the carriage return for teletypewriter ones)).