More UNIX

Pipes and redirection

Unix pipeline
Pipes - Send output of one program to input of other.
e.g. Search for all lines in the file that contain "DCU" in any case, except those containing "Computing" in any case, and sort the remaining lines:
```
cat file | grep -i dcu | grep -iv computing | sort
```
Backquotes - Capture the output of a program as a string.
Most common use is inside a shell script.
Use backquotes to capture output into a variable to use later.
```
x=`date`
echo "Current date is $x"
```

Redirection - Read input from a file, send output to a file.

prog < inputfile > outputfile

cat file | grep -i student > studentlist
cat file | grep -i staff   > stafflist

All these are the same:

grep string file
grep string < file
cat file | grep string

Append:
```
cat morestuff >> studentlist
```

Filename completion

Start typing filename, hit special key to complete it.

Linux - Tab
- If typing command - will search whole PATH for matches
- If just listing a file - will only search current dir
- If more than one choice - hit Tab twice to show
Solaris - Esc

Processes

ps                      See what processes are running
kill (process id)       Terminate some of your processes
kill -KILL (pid)        Definite kill
kill -1                 Kill all my processes

PPID              parent process of this process

ps (see man)
kill (see man)

xkill &                 Kill the next thing I click on      

nice			Run something at low priority deliberately
time			Time a run of some program

xkill (see man)
killall (see man)

Display of processes

Linux command line
- top (see man)
Linux GUI:
- System Monitor
Windows: Task Manager
Explanation of some of the data returned:
- paging and swapping
- threads
- GDI objects (Windows only)

ps in DCU

Login on lab PCs
- You each have your own CPU and memory, sharing a central filesystem.
  "ps" will show that the only processes running on the machine are yours and the Operating System's.
- ps -Tf
```
-T        associated with this terminal
-f        full details
```
- ps -u $USER -f
```
-u $USER  associated with this user
```
- ps -u $USER -o user,pid,ppid,comm,args
```
-o  Show these fields
```
ssh to student.computing.dcu.ie
- Shared CPU with other users.
- student.computing.dcu.ie is a Linux cluster, so some users have their own CPU, others are on shared CPUs, by chance.
- To see other people's processes:
  ps -Af
```
-A  all processes
```

Exercise with ps

Chrome from GUI:

Launch Chrome from the Linux GUI.
In command-line, type ps
Chrome is not in the list of processes. Why not?
How do you make a list of processes that includes Chrome?

Chrome from command-line:

Launch Chrome from command-line:
```
 google-chrome &  
```
ps now shows Chrome
It actually shows a program called "chrome" running, not "google-chrome".
So what is google-chrome? Type:
```
 which google-chrome 
```
Follow the trail of shortcuts to find the actual program.
The program is a shell script. Look inside it to find where "chrome" is and how it is launched.

Interrupts

Usage seems to vary on different variants of UNIX and Linux. You may get something like:


Ctrl-S                  Pause
Ctrl-C                  Interrupt
Ctrl-D                  Kill, Logout

Ctrl-Z                  EOF
 
q		exit man, more

Command-line Philosophy

A computer for programmers.

Unix philosophy
Provide lots of tools. String together tools with Shell logic, pipes, redirection.
If tools cannot do it alone, you can assemble a program to do it. "Program" may be just one line long.
all lower case - fast typing, don't have to hit Shift key
short command names - fast typing
Silence, "low-noise environment".
rm all my files, and it just does it. Doesn't even display a message saying they have been removed.
Note that backquotes would be useless if all programs displayed lots of informational messages as they executed.
Often an explicit prog -v "verbose" option if you want to see informational messages as it executes. But this is normally not the default.

GUI Philosophy

A computer for non-programmers.
(Or for a thing you want to do now for which a command-based approach is not appropriate.)

If it is not in the pre-defined tasks and menus, then you can't do it. You cannot assemble a program to do it.
High-noise.
rm all my files - dialog box comes up. Are you sure? OK.
(This dialog makes no sense in Unix - where a program, not a human user, might be issuing the command to rm files.)

Note that user interface people say these dialogs are often ignored.
From Donald Norman, The Psychology of Everyday Things, 1988, Ch.5:

Human - Delete all my most important files. System - Are you sure? Human - Yes Yes. System - Are you really sure? Human - Yes Yes. System - All your most important files deleted. Human - Oh damnit.

Compare with UNIX:

Human - Delete all my most important files. System - (Silence.) Human - Oh damnit.

Command-line on Mac / Windows

Windows always had DOS command-line, and still does.
But for many years it was neglected, not as powerful as UNIX command-line.
People who liked command lines tended to migrate to UNIX/Linux.
Recently, though, more powerful command shells have been introduced on Windows.
And now, Linux shell on Windows.
Mac for years had no command-line at all.
But now has UNIX command-line.
Typical modern Mac has powerful UNIX command-line with bash, csh.

From xkcd.