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I wanted to do a simple script to rename files, well parts of files. While the command works just fine from commandline:

find . -type f -name "*old*" -exec bash -c 'mv "$0" "${0/old/new}"' {} \; 2>&1 | grep -v "Permission denied" | grep -v "are the same file"

I tried to reimplement it in a shellscript:

#!/bin/bash
# renamefiles.sh - type renamefiles <old> <new>
# 
find . -type f -name "*$1*" -exec bash -c 'mv "$0" "${0/$1/$2}"' {} \; 2>&1 | grep -v "Permission denied" | grep -v "are the same file"

When user would type,

$ renamefiles old new

A failure would occur (with error message suppressing disabled):

mv: './File0_old.txt' and './File0_new.txt' are the same file
mv: './Another_old_file.txt' and './Another_new_file.txt' are the same file
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Let's start with two possible solutions first, then describe why you got the error.

Solution 1::

Just "temporarily" export the two variables so that they will be available to your sub-shell

#!/bin/bash
# renamefiles.sh - type renamefiles <old> <new>

export from="$1" && export to="$2" && find . -type f -name "*$1*" -exec bash -c 'mv "$0" "${0/$from/$to}"' "{}" \; 2>&1 | grep -v "Permission denied"


exit 0

So here we export $1 into variable from, and $2 into variable to. This way, the sub-shell will be able to read them.

Solution 2:: (simpler, and may be preferred by those who don't like the temporary export thingie)

#!/bin/bash
# renamefiles.sh - type renamefiles <old> <new>

find . -type f -name "*$1*" -exec bash -c 'mv "$0" "${0/$1/$2}"' "{}" "$1" "$2" \; 2>&1 | grep -v "Permission denied"

exit 0

This solution consists of just passing "$1" and "$2" besides {} (the current result from find) so that the sub-shell can access them normally as if it was a script on its own (with the exception that with the -c option passed to bash, the first argument would be $0 instead of $1; this seems to be known by you, as you've already used it)

Common notices regarding the two solutions::

  1. Always include an exit command at the end of your scripts
  2. Note the quoting for every variable being passed, even for {}. This would prevent misinterpretation for variables with spaces. Do this even if you're sure you don't have values or [here] filenames with spaces, as you don't know when you'll be later using your script.

Reason behind the error::

The reason behind the error you got ("are the same file") is very simple.

In your script, the mv command replaced the given file "$0" with another file given by the result of a string substitution ("${0/$1/$2}"). So in your case, $1 and $2 were not given to the sub-shell command, so it's like you did "${0//}" which would do nothing. As a result, the old and new filenames would be the same, hence the error.

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