Recursive chmod distinguishing files from folders

Version 3

An even better method is:
[cc_bash]
find "$target" -type f -exec chmod -c "$mode_files" {} \; \
-or -type d -exec chmod -c "$mode_dir" {} \;
[/cc_bash]A true one-liner! :D

Version 2

A better method is this:
[cc_bash]
find "$target" -type f -exec chmod -c "$mode_files" {} \;
find "$target" -type d -exec chmod -c "$mode_dir" {} \;
[/cc_bash]
This one can also be used from the command line.

Version 1

Many times I needed to apply certain permissions recursively on a given path but with different permissions on files than on directories (i.e. I want 0644 for files and 0744 for directories). This behaviour is not provided by the chmod tool so here is a simple and effective bash function to do just that:

[cc_bash]# Recursively apply chmod to path.
# If mode_files is missing then apply mode_dir to files too.
# Params: target mode_dir [mode_files]
function deep_chmod() {
function _walk() {
local F
for F in `find "$1"`; do
local M="$3"; [[ `file -b "$F"` == "directory" ]] && M="$2"
chmod -c "$M" "$F" > /dev/null
done
}
if [[ $# > 2 ]]; then
_walk "$1" "$2" "$3"
else
chmod -Rc "$2" "$1"
fi
}[/cc_bash]
I'm looking for a way to improve on this since it is quite costly for large directories: for each file or directory at least two programs are executed (file and chmod) which is not very efficient! For now, it gets the job done.
Enjoy! :)

Bash URI parser using SED

Warning! This version is now obsolete!
Check out the new and improved version (using only Bash built-ins) here!

Here is a command-line (bash) script that uses [cci lang="bash"]sed[/cci] to split the segments of an URI into usable variables. It also validates the given URI since malformed strings produce the text "ERROR" which can be handled accordingly:
[cc lang="bash" nowrap="true"]
# Assembling a sample URI (including an injection attack)
uri_1='http://user:pass@www.example.com:19741/dir1/dir2/file.php'
uri_2='?param=some_value&array[0]=123&param2=\`cat /etc/passwd\`'
uri_3='#bottom-left'
uri="$uri_1$uri_2$uri_3"

# Parse URI
op=`echo "$uri" | sed -nrf "uri.sed"`

# Handle invalid URI
[[ $op == 'ERROR' ]] && { echo "Invalid URI!"; exit 1; }

# Execute assignments
eval "$op"

# ...work with URI components...
[/cc]Notice the [cci_bash]"uri.sed"[/cci_bash] file given to [cci_bash]sed[/cci_bash]?

Recursive file/directory change-detection

Version 2

Another, much faster method would be to use [cci_bash]ls -lR[/cci_bash] to browse over the filesystem. On a newly installed Debian virtual machine (on Xen) hashing the entire filesystem (the root directory) took approximately 1.7 seconds. So, here it is: [cc lang="bash"]ls -lR "$D" | sha1sum | sed 's/[ -]//g' [/cc]

This method is sensitive to file name, size and modification size; usually that would be enough but if you need more control use...

Version 1

Detect when the contents of a file or directory ($D) changes: [cc lang="bash"]find "$D" | while read f; do stat -t "$f"; done | sha1sum | sed 's/[ -]//g' [/cc] This yields a hash of the current state of the file or directory which is extremely sensitive to even the most subtle changes (even a simple touch to any file/directory somewhere inside "$D" changes the generated hash).

Detect number of CPUs on a machine

UPDATE: Steven pointed out (very nicely) that there's no need for [cci_bash]cat[/cci_bash] in this picture, [cci_bash]grep[/cci_bash] would do just fine on its own. So, thanks Steven!

Detect how many CPU cores are present on the running machine:

[cc lang="bash"]
grep -c processor /proc/cpuinfo
[/cc]

This can be very useful when writing multi-threaded programs to properly match the number of threads with the number of CPU cores.