How do I invert group permissions using bash?-CodePudding

I'm trying to write a bash script that inverts the given file's group permissions. For example:

if file.txt had the permissions -rw-r--r--, it would be inverted to -rw--wxr--

if file.txt had the permissions -rw--w-r-x, it would be inverted to -rw-r-xr-x

I've done something similar to this in python before, where I used the XOR bitwise operator ^ to invert the execute permissions.

I can't seem to figure out the proper way of doing this in bash The filename will be provided as a command line argument

CodePudding user response：

Would you please try the following:

#!/bin/bash

fname=$1                                # filename is given at the command line
perm="0$(stat -c %a "$fname")"          # permissions in oct such as 0644
iperm=$( printf "0%o" $(( perm ^ 070 )) )
                                        # invert the group permissions such as 0634
chmod "$iperm" "$fname"                 # update the file status