UNIX for Dummies Questions & Answers

#!/bin/sh
find /abc -type f | while read filename
do
  sed 's/pqr/uvw/g' < $filename > ${filename}.modified
  mv ${filename}.modified $filename    # omit this line if you want to keep both versions
done

find /abc -name 'file*.txt -type f |
while read filename
do
    sed 's/pqr/uvw/g' $filename > tmp.tmp
    mv tmp.tmp $filename
done

E.g.

a/abc/file1.txt
a/abc/def/ijk/file2.txt
a/abc/def/ghi/klm/file3.txt
a/abc/xyz/mno/klm/file4.txt
a/abc/rst/ghi/file1.txt


find ./abc  -name "*"  -type f |while read filename
do
    sed 's/^M//g' $filename > tmp.tmp
    mv tmp.tmp $filename
done