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Completely safe find

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safe-find.sh
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#!/bin/bash
# Filenames can contain *any* character except only null (\0) and slash (/);
# here's some general rules to handle them:
#
# $'...' can be used to create human readable strings with escape sequences.
#
# ' -- ' in commands is necessary to separate arguments from filenames, since
# filenames can start with '--', and would therefore be handled as parameters.
# To handle parameters properly (like GNU tools) use `getopt`.
#
# `find` doesn't support this syntax, so we use `readlink` to get an absolute
# path which by definition starts with slash.
#
# The "$()" construct strips trailing newlines, so we have to add a different
# character and then strip it outside the "$()" construct.
#
# `IFS=` is necessary to avoid that any characters in IFS are stripped from
# the start and end of $path.
#
# '-r' avoids interpreting backslash in filenames specially.
#
# '-d $'\0' splits filenames by the null character.
#
# '-print0' separates find output by null characters.
#
# Variables inside '$()' have to be quoted just like outside this construct.
#
# Use process substitution with "<(" instead of pipes to avoid broken pipes.
#
# Use file descriptor 9 for data storage instead of standard input to avoid
# greedy commands like `cat` eating all of it.
 
set -o errexit
set -o nounset
set -o noclobber
 
test_file_name=$'--$`\! *@ \a\b\e\E\f\r\t\v\\\"\' \n'
test_dir_path="$test_file_name"
test_file_path="${test_dir_path}/${test_file_name}"
 
mkdir -- "$test_dir_path"
touch -- "$test_file_path"
 
absolute_dir_path_x="$(readlink -fn -- "$test_dir_path"; echo x)"
absolute_dir_path="${absolute_dir_path_x%x}"
 
exec 9< <( find "$absolute_dir_path" -type f -print0 )
while IFS= read -rd $'\0' -u 9
do
file_path="$(readlink -fn -- "$REPLY"; echo x)"
file_path="${file_path%x}"
echo "START${file_path}END"
done
 
rm -- "$test_file_path"
rmdir -- "$test_dir_path"

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