Search and replace in UNIX

How would i replace a string in a file such that the string to be replaced is always succeeded by 开发者_如何学编程some string.

eg: If i want to replace ABC with 123 as below,

INPUT

ABC
ABCXYZ
ABCDHD
ABC
CDE

OUTPUT

ABC
123XYZ
123DHD
ABC
CDE

i tried using sed but with no success.

---

Without capture using look-ahead:

s/ABC(?=\S)/123/;

---

sed -i 's/ABC\(.+\)$/123\1/g' myFile.txt

ABC, match the literal ABC!

\(.+\) match at least 1 other character capture it in group 1

123\1 replace the hole thing with 123 followed by what is captured in group 1

---

perl -pi.bak -e 's/^ABC(.+)$/123$1/g' file.txt

This will however replace whitespace too. If you do not want that, instead of .+ you can use \S+.

The -i.bak option will save a backup of file.txt in file.txt.bak, in case you bungled the replace.

---

this one worked for me:

$ sed   -r  s/ABC\(.+\)/123\\1/g <file>
ABC
123XYZ
123DHD
ABC
CDE

---

Surprised that no-one has used \B.

#!/usr/bin/perl

use strict;
use warnings;

while (<DATA>) {
  s/ABC\B/123/;
  print;
}

__DATA__
ABC
ABCXYZ
ABCDHD
ABC
CDE