First of all I needed a few commands for my script. They were:

chown -R username:groupname dirname
chmod -R flags dirname

Where

• dirname is the name of the destination directory
• username is the name of the owner that will own the directory
• groupname is the name of the group that will own the directory
• flags is the numerical value for the permissions of the directory
• -R specifies that the operation will occur recursively for all children of the directory

Next step was to retrieve the current values for an existing file or directory that I know I wanted to copy the permissons from. For that, I can use the stat command with a format string:

stat -c%u:%g filename
stat -c%a filename

Where

• filename is the existing file (or directory)
• -c specifices that the output of the command should include and be formatted according to the following format
• %u means the id of the user that owns the file
• %g means the id of the group that owns the file
• %a means the numerical value for the permissions of the file

Next, I needed to provide the output of the stat commands as input (or part of the input) to the chown and chmod commands. This is done with Bash using the following notation:

command $(command-with-output)

This led me to the following commands:

chown -R $(stat -c%u:%g source) destination
chmod -R $(stat -c%a source) destination

If you specify your own source and destination, these commands can be run from the Bash prompt. But I also wanted to put them inside a Bash script so I didn’t have to do all this typing. I also added some validation and came up with the following script:

#!/bin/bash
if [ -z $1 ] || ([ ! -d $1 ] && [ ! -f $1 ]); then
  echo "Not a file or directory as first argument"
  exit 0
fi
if [ -z $2 ] || [ ! -d $2 ]; then
  echo "Not a directory as second argument"
  exit 0
fi
chown -R $(stat -c%u:%g $1) $2
chmod -R $(stat -c%a $1) $2

Some things to note from the script:

• -z is true if the following variable is empty (zero length)
• -d is true if the following variable is a directory
• -f is true if the following variable is a directory
• ! negates the condition
• || means “or” and && means “and”
• The semicolon before “then” is important, but can be omitted if “then” is moved to a line of its own

This script has served me well. I hope you’ll find it useful too.