How can I remove the last character of a file in unix?

Question

Say I have some arbitrary multi-line text file:

sometext
moretext
lastline

How can I remove only the last character (the e, not the newline

Answer 1

EDITED ANSWER

I created a script and put your text inside on my Desktop. this test file is saved as "old_file.txt"

sometext
moretext
lastline

Afterwards I wrote a small script to take the old file and eliminate the last character in the last line

#!/bin/bash
no_of_new_line_characters=`wc  '/root/Desktop/old_file.txt'|cut -d ' ' -f2`
let "no_of_lines=no_of_new_line_characters+1"
sed -n 1,"$no_of_new_line_characters"p  '/root/Desktop/old_file.txt' > '/root/Desktop/my_new_file'
sed -n "$no_of_lines","$no_of_lines"p '/root/Desktop/old_file.txt'|sed 's/.$//g' >> '/root/Desktop/my_new_file'

opening the new_file I created, showed the output as follows:

sometext
moretext
lastlin

I apologize for my previous answer (wasn't reading carefully)