If we just stick with standard sed addressing constructs and do not depend on non-standard options, you could try something more like:

Code:

#!/bin/ksh
IAm=${0##*/}
tmpf="$IAm.$$"

trap 'rm -f "$tmpf"' EXIT

cd /home/user/bharat
for file in *.RET
do	printf 'File Name=%s\n' "$file"
	sed -e 1n -e '$n' -e 's/./I&/180' "$file" > "$tmpf" && cp "$tmpf" "$file"
done

Note that your description talks about INSERTING a character in the 180th position which I interpret to mean "insert a character before the 180th character on the existing line" while none of your sample input files have 180 characters in any line and all of the samples that have shown examples using character position 10 instead of 180 have been "appending a character after the 10th character" instead of "inserting a character before the 10th character. The above code attempts to "insert a character before the 180th character on lines 2 through n-1, inclusive, for a file that contains n lines.

The code samples you have shown unconditionally move the output produced by sed to the input file whether or not sed succeeded or failed. The above code only modifies the input file if the sed command completes successfully. Furthermore, it copies the updated file back to the original file (which preserves file permissions and hard links) while the moves used by your script will break any hard links to your input files and may destroy the contents of your input file if sed fails for any reason.

Hopefully, this will work better for you.

Note that it is always a good idea to tell us what operating system and shell you're using so the volunteers here trying to help you can avoid suggestions that won't work in your environment.

The previous script was written and tested using a Korn shell, but will work with any shell that is based on Bourne shell syntax and performs parameter expansions required by the POSIX standards (such as ash, bash, dash, ksh, and zsh).