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Test speaker channels
Useful tool to test if all speaker channels are working properly. speaker-test is part of alsa-utils package

List all symbolic links in a directory matching a string
Finds all symbolic links in the specified directory which match the specified string pattern. I used this when upgrading from an Apple-supported version of Java 6 (1.6.0_65) to an Oracle-supported version (1.7.0_55) on Mac OS X 10.8.5 to find out which executables were pointing to /System/Library/Frameworks/JavaVM.framework/Versions/Current/Commands (Apple version) vs. /Library/Java/JavaVirtualMachines/jdk1.7.0_55.jdk/Contents/Home/bin (Oracle version). However, it appears the current JDK installation script already takes care of modifying the links.

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

Use a var with more text only if it exists
See "Parameter Expansion" in the bash manpage. They refer to this as "Use Alternate Value", but we're including the var in the at alternative.

grep for minus (-) sign
Use flag "--" to stop switch parsing

Retrieve a list of all webpages on a site
This spiders the given site without downloading the HTML content. The resulting directory structure is then parsed to output a list of the URLs to url-list.txt. Note that this can take a long time to run and you make want to throttle the spidering so as to play nicely.

Pretty man pages under X
You're a developer - but it doesn't mean you have to slum it! Why not spice up your man page lookups by using a decent PDF viewer. I use 'xpdf' - maybe you prefer acroread, whatever, it's just as fast as plain dull ASCII on today's machines and you can still search for stuff - that's the main reason I use PDF and not PS.

Re-use the previous command output
The $(!!) will expand to the previous command output (by re-running the command), which becomes the parameter of the new command newcommand.

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

'hpc' in the shell - starts a maximum of n compute commands modulo n controlled in parallel, using make
this oneliner uses make and it's jobserver for parallel execution of your script. The '-j' flag for make defines number of subprocesses to launch, '-f' tells make use stdin instead of Makefile. Also make have neat flag '-l', which "Specifies that no new jobs (commands) should be started if there are others jobs running and the load is at least load (a floating-point number)." Also you can use plain Makefile, for better readability: targets = $(subst .png,.jpg,$(wildcard *.png)) $(targets): echo convert $(subst .jpg,.png,$@) $@ all : $(targets)


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