Commands using echo

Ummmm.. Saw that gem on some dead-head hippies VW bus at phish this summer.. It's actually one of my favorite ways of using bash, very clean. It shows what you can do with the cool advanced features like job control, redirection, combining commands that don't wait for each other, and the thing I like the most is the use of the ( ) to make this process heirarchy below, which comes in very handy when using fifos for adding optimization to your scripts or commands with similar acrobatics.

F UID PID PPID WCHAN RSS PSR CMD

1 gplovr 30667 1 wait 1324 1 -bash

0 gplovr 30672 30667 - 516 3 \_ sleep 3

1 gplovr 30669 1 wait 1324 1 -bash

0 gplovr 30673 30669 - 516 0 \_ sleep 5

1 gplovr 30671 1 wait 1324 1 -bash

0 gplovr 30674 30671 - 516 1 \_ sleep 7

This is helpful for shell scripts, I use it in my custom php install script to schedule to delete the build files in 3 hours, as the php install script is completely automated and is made to run slow.

Does require at, which some environments without crontab still do have.

You can add as many commands to the at you want. Here's how I delete them in case the script gets killed. (trapped)

atq |awk '{print $1}'|xargs -iJ atrm J &>/dev/null

Very very cool list of quotations and directives on pythonic programming. I love them and they are sure applicable in C++ too, and for most any programming, really.

This will email user@example.com a message with the body: "rsync done" when there are no processes of rsync running. This can be changed for other uses by changing $(pgrep rsync) to something else, and echo "rsync done" | mailx user@example.com to another command.

http://localhost/test.php

Gets the internal and external IP addresses of all your interfaces, or the ones given as arguments

The Linux kernel uses unused memory in caches. When you execute "free" you never get the "real" available memory.

This command uses mutt to send the mail. You must pipe in a body, otherwise mutt will prompt you for some stuff. If you don't have mutt, it should be dead easy to install.

This works in some situations where 'reset' and the other alternatives don't.

NAME

rev - reverse lines of a file or files

SYNOPSIS

rev [file ...]

DESCRIPTION

The rev utility copies the specified files to the standard output, reversing the order of characters in every line. If no files are specified, the standard input is read.

AVAILABILITY

The rev command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

This command starts screen with 'htop', 'nethogs' and 'iotop' in split-screen. You have to have these three commands (of course) and specify the interface for nethogs - mine is wlan0, I could have acquired the interface from the default route extending the command but this way is simpler.

htop is a wonderful top replacement with many interactive commands and configuration options. nethogs is a program which tells which processes are using the most bandwidth. iotop tells which processes are using the most I/O.

The command creates a temporary "screenrc" file which it uses for doing the triple-monitoring. You can see several examples of screenrc files here: http://www.softpanorama.org/Utilities/Screen/screenrc_examples.shtml

Resizes all images in the curent directory to x resolution.

It is better than `mogrify -resize *.jpg` because of independence from extension of image (e.g. .jpg and .JPG) (:

Only tested on Linux Ubunty Hardy. Works when file names have spaces. The "-maxdepth 2" limits the find search to the current directory and the next one deeper in this example. This was faster on my system because find was searching every directory before the current directory without the -maxdepth option. Almost as fast as locate when used as above. Must use double quotes around pattern to handle spaces in file names. -print0 is used in combination with xargs -0. Those are zeros not "O"s. For xargs, -I is used to replace the following "{}" with the incoming file-list items from find. Echo just prints to the command line what is happening with mv. mv needs "{}" again so it knows what you are moving from. Then end with the move destination. Some other versions may only require one "{}" in the move command and not after the -I, however this is what worked for me on Ubuntu 8.04. Some like to use -type f in the find command to limit the type.

When you've got a list of numbers each on its row, the ECHO command puts them on a simple line, separated by space. You can then substitute the spaces with an operator. Finally, pipe it to the BC program.

Useful when you have some wrong on a server (nfs freeze/ immortal process)

Create a bunch of random files with random binary content. Basically dd dumps randomly from your hard disk to files random-file*.

Display the amount of memory used by all the httpd processes. Great in case you are being Slashdoted!

slashdot.org webserver adds an X-Bender or X-Fry HTTP header to every response!

A common mistake in Bash is to write command-line where there's command a reading a file and whose result is redirected to that file.

It can be easily avoided because of :

1) warnings "-bash: file.txt: cannot overwrite existing file"

2) options (often "-i") that let the command directly modify the file

but I like to have that small function that does the trick by waiting for the first command to end before trying to write into the file.

Lots of things could probably done in a better way, if you know one...