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Say you have a directory with a bunch of sub directories and files and you want to see if all the files are owned by a particular user, you can use the following set of commands

[code]ls DIRECTORY_PATH -l -R | awk {‘print $3’} | grep -v USER_NAME[/code]

The set of commands do the following

• ls -l -R shows the list of files and directories
• awk prints the name of the owner of the file (it is the third column)
• grep shows only the lines where the owner name doesn’t match

And yeah.. this works in most variants of Linux :).

I was looking for a quick way to search for credit card numbers in a file and ran across this excellent post by Adrian Rollett. I tweaked his suggestion a bit to show some additional data.

Original suggestion

[code] grep ‘\(^\|[^0-9]\)\{1\}\([345]\{1\}[0-9]\{3\}\|6011\)\{1\}[-]\?[0-9]\{4\}[-]\?\[0-9]\{2\}[-]\?[0-9]\{2\}-\?[0-9]\{1,4\}\($\|[^0-9]\)\{1\}’ FILE_TO_SEARCH [/code]

My modification

[code] grep ‘\([345]\{1\}[0-9]\{3\}\|6011\)\{1\}[ -]\?[0-9]\{4\}[ -]\?[0-9]\{2\}[-]\?[0-9]\{2\}[ -]\?[0-9]\{1,4\}’ –color -H -n FILE_TO_SEARCH [/code]

The modified command will show the name of the file the number was found and at which line. You can tweak it further using additional options for grep. A good reference guide can be found here.