Tips and tricks on using the command line. (Page 1 of 2)

I wish to introduce four new topics to this topic. They are piping, redirection, jobs, and multi-command stacking.
Piping is the process of taking the output of one program and passing it as the arguments to another program. An example would be passing a large amount of output from, say, cat to more, a command-line and easy-to-use pager:
cat /etc/passwd | more
The vertical bar (or pipe) (|) character is used to indicate that you wish to pipe the output from one program to another.
The syntax is as follows:
program | program
Piping can also be used to create what is known as a pipe chain. Pipe chains are multiple programs piped to one after another in order. The syntax is as follows:
program | program | program | program | program | program | program | <...>
The chain can be an indefinite amount of piped programs, although you are usually limited by your shells maximum input length (which is usually 8,192 characters).
Redirection is the process of either directing the data from one file (input redirection) to a program as input or directing the output of a program (output redirection) to a file. Input redirection comes in only one form, while output redirection comes in four forms. The left angle bracket (<) and the right angle bracket (>) are used to control this redirection. The syntax for input redirection is:
program < file
where "program" is a program to execute and "file" is the redirected file. The syntax for output redirection is a bit more complicated, but is below:
Redirect STDOUT to a file, recreating the file and writing the new data into the recreated file:
program > file
Redirect STDERR to a file, recreating the file and writing the new data into the recreated file:
program 2> file
Redirect STDOUT to a file, appending the contents of STDOUT to that file without erasing the previously existing content of the file:
program >> file
Redirect STDERR to a file, appending the contents of STDERR to that file without erasing the previously existing content of the file:
program 2>> file
Note: Whitespace does matter when using this type of redirection. For instance, > > is considered two separate things than >> is. Similarly, 2 >>, 2> >, and 2 > > are all separate entities, while 2>> is not (and is used as a normal STDERR redirection operator).
Jobs are a very interesting topic, and are widely used on Linux shells such as BASH. They are not available on Windows. To create a job, run the following command, replacing program and [arguments] with the actual program name and arguments:
program [arguments] &
For instance, to compile a massive program that uses a makefile in the foreground (but allowing you to do other things while the compilation goes):
make -s &
The ampersand (&) character is used to signify that you wish for this task to be a job. After pressing enter, you will see something like:
[1] 21238
The [1] is the Job ID. This is used when terminating jobs, although PIDs are much better than job specifications. The 21238 is the process ID. Always keep this in memory; this job may need to be terminated at some point, and pressing control+C will not terminate this job like a normal programs execution would.
You can manage the jobs foregroundness and backgroundness by using the bg and fg commands. The syntax is:
Return the currently active job to the foreground:
fg
Return the currently active job to the background:
control+Z and then bg
The control+Z key combination is used to turn a currently foreground application into a job task. You see something like:
[1] +stopped make -s
The [1] is the Job ID. The + character is used to indicate that a new job has been added to the job queue. The stopped message indicates the process state, and the make -s is the command. When a process is stopped like this, it is not truly terminated; rather, it is simply suspended -- it's memory space is still registered and in-use by the suspended task. To resume the task, use either the fg (foreground) or bg (background) commands. Passing fg or bg an argument signifies that you wish that job ID to go into the foreground (come to front) or the background (send to back). This must be a valid Job ID. Job IDs are also known as 'jobspecs'.
Multi-command stacking is the process of using conditional operators to signify what the operating system should do if a particular exit code is returned when a program exits. The exit code is an integral value that signifies the process's status when it exited. Traditionally, the exit code zero (0) indicated (and still does indicate) success, while a positive or negative exit code signified (and still does signify) an error of some kind. For you C/C++ programmers out there, the exit code is usually stored in the ERRNO constant in the parent process's memory space. In BASH, the $? variable signifies the last executed command's exit code. The operators usable in multi-command stacking are as follows:
&& (and): Execute the next command on the right-hand side of the operator only if the command on the left-hand side of the operator succeeds (exits with a success exit code).
|| (or): Execute the command on the right-hand side of the operator only if the command on the left-side of the operator exits with a non-success error code (non-zero exit code). If the process on the left-hand side of the operator exits with a success exit code, the command on the right-hand side of the operator will not be executed.
These are the only operators I know of and have used successfully.

So I've been looking for mention of PBX and Asterisk when this question came up.
Should we start making a list here of SSH and SFTP commands so people who want to start using Linux like Ubuntu on a VPS can have some sort of idea on where to begin?
When I first logged in, I was told to type 'apt-get update', where it would refresh the list of repositories and look for pacakges in the http://archive.ubuntu.com/
Once the search is complete, type 'apt-get upgrade',, which will install all of the packages that need updating.
If you want to search for a specific package using the advanced package tool, which is what apt stands for, type 'apt-cache search packagename Example: 'apt-cache search samba'. If the package exists, I believe you type 'apt-get install packagename'. Some packages have extra things. For example, if you're installing Apache, My SQL, and PHP, you'd specify the type of PHP package you want with a dash. Like this. 'apt-get install php-nameofsubpackage'
Note, I used the single quotation mark so you can see where the commands start and end. For this I am using Secure CRT, which is portable, and supports multiple protocols.

have both cmd and bash tricks for you people.
Windows trick:
the cd command is limited to the current drive. Type the drive letter and a colon to switch to another drive, note that your current directory is drive specific! Which is sweet btw...
In windows 10, you can now press control v to paste into cmd, although putty doesn't like this. Control c still sends it's char because it kinda has to!
pushd and popd are useful, especially for working with UNC paths.
Unix style paths work on windows, for example "cd /" changes to the root of your current drive, I always find myself using / instead of backslash, which makes some programs have a fit...
if you use the dir command to list a directory and you don't like all the extra output, add a /b switch and it'll list it like ls, just the filenames and foldernames in it.
if you wish to remove a directory, use rmdir, or rd. If the directory is not empty it will yell at you, "rd /s" fixes that. Also del has a /s switch, which does recursive deletion, here's a practical example.
cd %userprofile%\documents\sfx
del /s *.sfk
del /s *.sfl
del /s *.reapeaks
you will get spammed with output, you could try using > nul, maybe? But it will delete all those stupid files audio editors generate.
bash:
A particular command I use if I wish to run a game server compiled for windows on linux, that doesn't terminate when I kill the ssh session, looks like this. Note that you need no additional packages except of course wine.
nohup wine server.exe &
the nohup makes it not receive a hang up signal, which will make it less likely to die when you close your ssh, and won't make it run in your console. The '&' on the end there is something strange that makes it run completely background, meaning you can log off and it'll keep going! To make it die, use pkill wine, or I believe pkill server.exe also works.
if you're making windows batch files, @echo off is a very common line to use, to make the command shell not log your commands but only the output.
Another command used in batch files is "setlocal enableextensions" which makes all environment variable changes local so you can store temp stuff that stays temp, and enableextensions does something that I don't really know much about.
A nice command in batch files if you wish to prompt the user for some input instead of making them specify it as an argument to the batch file, so they can press enter on it, is the following.
set /p inp="enter some text here"
rem just throw it back at them
echo %inp%
That could be used for a youtube-dl batch file... Hehe!
Windows has three different copy commands for different things. Copy, xcopy and robocopy. Use their corresponding /? switches, and make sure you redirect to a file because the output of those commands is several pages long and your cmd will flat wrap.
If you wanna shut down your computer, and be cool and/or quick about it, use
"shutdown.exe /s /t 00 /f"
you could also use /r instead of /s to make it reboot.
If you want to add a filetype, such as .py, .pl etc to your execution path so you can click on them from explorer and they will just run, once you've configured to open them with their interpreter obviously, open an admin command prompt and use this one.
set pathext="%pathext%;.stuff"
You'll have to log out and back in for that to work.
I'm still struggling with the exact syntax for the ftype and assoc commands, but they're fun to use, because they're a quick and painless way to register a file extension to be opened by a program without the windows explorer dialog crap. I actually used it once to associate all the dependency files for rhythm rage levels with notepad, because you can have more than one extension associated with the same type! You have to use multiple assoc commands though.
Again for batch file people, who  don't use it and you want to run a program that does it's own thing from a batch file, use the start command so it doesn't hang up your batch file.
the title command is useful btw, changes the title of your prompt so it can cram it's path up it's binary ass.
if you are doing batch files and you want the user to press a key before something happens, pause. It freezes your batch file until they hit a key, prompting them with "press any key to continue..."
And for people who are programming and want cmd to do something, cmd itself has two switches. /c and /k. /c executes a command and closes, /k executes a command and leaves it open, useful for examining output but unfortunately also reprompting the user with the do stuff prompt... Maybe try either using > to output stuff to a temp file or if it's possible grab it's stdout/stderr directly.
Sorry for the spam, just thought of all that shit on the fly in bursts. Enjoy!

I'll give a description of what command does; I'll leave you to find out how they work on your own, because that's how everyone best learns.

• Find Files by Name: find -name

• Find Files by Ownership: find -user

• Find Files by File Size: find -size

• Find Files by File Type: find -type

• Find Files by Time: find {-amin|-cmin|-mmin|-atime|-ctime|-mtime|-anewer|-cnewer|-newer|-newerXY} (|=or and {/} means required)

• Show Results If the Expressions Are True (AND): find -a

• Show Results If Either Expression Is True (OR): find -o

• Show Results If the Expression Is Not True (NOT): find -n

• Execute a Command on Found Files: find -exec

• Execute a Command on Found Files More Efficiently: find + (or) find | xargs

• Execute a Command on Found Files Containing Spaces: find -print0 | xargs -0

• View Your Command-Line History: history

• Run the Last Command Again: !!

• Run a Previous Command Using Numbers: ![##]

• Run a Previous Command Using a String: ![string]

• Search for a Previous Command and Run It: ^-r (Ctrl-r) (or) ^-s (Ctrl-s) (or) ^-g (Ctrl-g)

• Display All Command Aliases: alias

• Discover How Long Your Computer Has Been Running: uptime

I'll add more as I go along. That's certainly not all I know!

hey turtlepower17, by all means, we do wanna hear about ip config, because i often use it, and forget half the stuff I can do with it in a crunch, this is a valuable topic and I can always use this to help me quickly look up some commandsI need. so go right ahead and post em for us. .

How are Mac and Linux different if they use Unix structure? Windows does not use Unix, so it uses a dos command-line structure I think.

For Mac users, if you downloaded the applications from outside the App Store, when you try to open it, you may get an error message stating that the file is damaged and can't be open. And then it gives you the option to move the file to the trash. That because of the Gate keeper. to fix this, open Terminal, and type the following:

sudo xattr -rd com.apple.quarantine /Applications/Lockedapp.app.

For example, if I had an application called "Bla.app", and if Gate keeper blocked this app, I would type this command into Terminal:

sudo xattr -rd com.apple.quarantine /Applications/Bla.app, and hit enter.

Note: You will need to enter your password to make changes to the system.

Hope this helps for new Mac users who having trouble run certain apps on their system.

I really only know Windows, but there are a few that I do.

This command allows you to make a bootable USB from an image on your hard drive.

EG: WIndows PE or Installer media.

Xcopy x:\source /s /e /f Y:\

X and Y being your source and destination drives.  Just be sure your destination drive is the root directory of the USB stick or it will not work.  No need for third party tools.  I've used this method plenty of times.

On windows one of the most useful commands I've seen is the taskkill command. It needs a few switches: /f (force), /pid <process> the process. For example to kill the firefox process you would use taskkill /f /pid firefox.exe. i've used this quite a lot when a program crashes so badly that NVDA stopped responding.

I'm pretty sure both of these can be run by right clicking the drive name in windows explorer, no?  At least the first one can be.

Either way, they are useful things to know.

@22, because it makes locating the PID unnecessary. If NVDA stops responding, I don't need to restart it to do it -- I just enter the image name into taskkill and hope to got it works. I do that on linux too - kill -9 `pgrep <processname>`.