Using a variable with rename command

Question

I want to use the rename command to remove characters on a file basename, based on characters entered (input) by the user in an interactive script.

Basically, I would like to do this:

read characters_to_remove_inputted_by_the_user

rename 's/$characters_to_remove_inputted_by_the_user//g' file

But I'm having trouble with properly inserting the variable and keep the command structure during the script execution.

Answer 1

Assuming -- as your own command line suggests -- perl's rename implementation (an example script shipped with perl since version 3 in 1989, and often included as a command in many OSes, sometimes as a rewrite with extensions separate from the perl package like this one), sometimes called prename on some Linux distributions where rename is otherwise the one from util-linux, you can use the environment:

STRING=$characters_to_remove_inputted_by_the_user rename 's/\Q$ENV{STRING}\E//g' ./*

Above, the content of the $characters_to_remove_inputted_by_the_user shell variable is passed as the value of the STRING environment variable which perl retrieves with $ENV{STRING}.

Alternatively, you could use the export shell special builtin so that that shell variable be passed in the environment of every command it executes including that rename:

export characters_to_remove_inputted_by_the_user
rename 's/\Q$ENV{characters_to_remove_inputted_by_the_user}\E//g' ./*

The \Q/\E are to make sure $STRING is treated as a fixed string and not a regexp. If you want it to be treated as a regexp, that's just:

REGEXP=$characters_to_remove_inputted_by_the_user rename 's/$ENV{REGEXP}//g' ./*

Avoid things like:

rename "s/$characters_to_remove_inputted_by_the_user//g" ./*

Above the content of the shell variable is expanded by the shell before calling rename, so that could amount to a command injection vulnerability, as the value of the variable would be interpreted as perl code (think for instance of a value like //;system("reboot");s/).

Answer 2

With util-linux rename:

$ touch myfile1
$ ll
total 0
-rw-rw-r--. 1 fpm fpm 0 Mar 25 15:30 myfile1
$ read DELCHARS
my
$ rename -- "$DELCHARS" "" myfile1
$ ll
total 0
-rw-rw-r--. 1 fpm fpm 0 Mar 25 15:30 file1
$