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extract email adresses from some file (or any other pattern)
This will catch most separators in the section of the email: dot . dash - underscore _ plus + (added for gmail) ... and the basic dash '-' of host names.

Quick notepad
Quick write some notes to a file with cat. Ctrl+C when you have finish.

Exclude inserting a table from a sql import
Starting with a large MySQL dump file (*.sql) remove any lines that have inserts for the specified table. Sometimes one or two tables are very large and uneeded, eg. log tables. To exclude multiple tables you can get fancy with sed, or just run the command again on subsequently generated files.

Monitor system load and print out top offending processes
This checks the system load every second and if it's over a certain threshold (.8 in this example), it spits out the date, system loads and top 4 processes sorted by CPU. Additionally, the \a in the first echo creates an audible bell.

Delete Mailer-Daemon messages

Display the number of connections to a MySQL Database
Count the number of active connections to a MySQL database. The MySQL command "show processlist" gives a list of all the active clients. However, by using the processlist table, in the information_schema database, we can sort and count the results within MySQL.

Generate random valid mac addresses
Ruby version. Also, a perl version: $perl -e 'printf("%.2x.",rand(255))for(1..5);printf("%.2x\n",rand(255))'

Sorted, recursive long file listing
Tells you everything you could ever want to know about all files and subdirectories. Great for package creators. Totally secure too. On my Slackware box, this gets set upon login: $ LS_OPTIONS='-F -b -T 0 --color=auto' and $ alias ls='/bin/ls $LS_OPTIONS' which works great.

Replace all tabs with spaces in an application
Note that this assumes the application is an SVN checkout and so we have to throw away all the .svn files before making the substitution.

Jump to a directory, execute a command and jump back to current dir


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