mjhjmtu

A simple shell script is needed to copy dotfiles, adding a .backup extension, i.e., .dotfile1.backup. The script below will not work because it adds extensions to pre-existing backups forever and ever, i.e., .dotfile1.backup.backup.

bkdot.sh

#!/bin/sh
for file in .*; do
 cp “./$file” “./$file.backup”
done

The next script seems like it should solve the problem, but nothing happens at all. What is it missing?

bkdot_revised.sh

#!/bin/sh
for file in .*; do
 if [ ! “./$file.backup” ]; then
 cp “./$file” “./$file.backup”
 fi
done

The ! operator just negates it's operand so the condition always evaluates to false.
There are file test operators, -f for instance that returns true if file exists.

However I'm not sure you are doing this right, neither only making backup if it doesn't exist nor always overwriting existing backups is secure.

Could do this way.

#!/bin/sh
for file in .*; do
 if [ ! -f "./$file.backup" ]; then
 cp "./$file" "./$file.backup"
 fi
done

The test [ doesn't have enough information. You need to compare $file to a reference. You current construct says "if not this string", but you need to say "if x is not this string". I would use a regex, i.e. with [[ instead of [. Hence,

#!/bin/bash
GLOBIGNORE=.:..
for file in .*; do
 if [[ ! "$file" =~ .backup$ ]]; then
 cp "$file" "$file.backup"
 fi
done

• As per Kusalananda's comment, I moved the shebang to /bin/bash, to ensure the [[ construct works.


• As per Gordon Davisson's comment, I added the GLOBIGNORE, so that the script doesn't attempt to copy . and ..
  

A few other things:

• 
  ./ in the paths is unnecessary. You are already in this directory!


• I'm not sure if it was just a copy-paste issue, but you had “ instead of ".


• Personally, I would just copy into another directory, and avoid all these issues, and avoid polluting my home directory. Actually, I would just (incrementally) backup everything instead!

Here is a pure /bin/sh version. Instead of using the [[ bashism, I've used case instead.

#!/bin/sh
GLOBIGNORE=.:..
for file in .*; do
 case "$file" in
 *.backup) ;;
 *) cp "$file" "$file.backup";;
 esac
done

Why don't we simply use sed to backup?

sed -i.bak 's#n#n#' <filepattern*>