Replacing a string with sed 1

[Calator]

following script to perform string substition with 'sed' does not work, can anyone see what the problem is? thanks

#!/bin/ksh
# a file has a header record followed by detail records;
# variable text in positions 1-19 on all detail records must be changed to some constant text

# pattern to be replaced is obtained from record no. 2 positions 1-19:
source_file=$1
tmp_file=$source_file$$
oldtext="`sed -n -e '2p' ${source_file} | cut -c1-19`"

newtext="CHANGED TEXT"

echo $oldtext $newtext

sed '2,$ s/${oldtext}/${newtext}/g' ${source_file} > ${tmp_file}

mv $tmp_file $source_file

 

[vgersh99]

change single-quotes to double-quotes in your sed.

vlad
+----------------------------+
| #include<disclaimer.h> |
+----------------------------+

 

[Calator]

Thanks Vlad,

That's fixed it.
However could you explain why the following single-quoted code is working:
old_user="048135"
new_user="048141"
sed '1,1 s/${old_user}/${new_user}/g' ${source_file} > ${tmp_file}

 

[vgersh99]

it should NOT - you may not have anything to substitute on the FIRST line.

vlad
+----------------------------+
| #include<disclaimer.h> |
+----------------------------+