Unix crashcourse

Apr 1, 2015 • unix, shell, and shellpower

Following is a list of basic shell commands for Unix:

ls -l

Outputs

drwxr-x---   2 akarki15 akarki15       6 Jun  2  2011 bin
-rw-r-----   1 akarki15 akarki15 4194304 Apr 22  2014 block-device.data
drwxrwxr-x  17 akarki15 akarki15    4096 Feb 28  2014 cs111
drwxr-x---  19 akarki15 akarki15    4096 May 28  2014 cs112
drwxr-x---   6 akarki15 akarki15     147 May 10  2014 cs-261
drwxr-x---   3 akarki15 akarki15      18 May  1  2013 CS281

First column of the output is showing access rights
1. rwx: read, write, executable
2. Three sets of them for user, others in the group, and everyone

How do you change the access settings?

chmod u+w will give write rights to users in the group
chmod o+x will give executable rights to others in the group
chmod a-r will take away read rights from all in the group

Some switches for ls

Command	Description
`ls -a`	shows “all” files
`ls -d a*`	Wildcard to display all files whose filename begins with a
`ls -d [i-l]*`	[i-l] is a set containing letters i through l

Cool things you can do with dot dot (..) and tilde (~)

.. represents the parent director. So say you are in /home/aashish and /home has another file called a.java. You can access it from aashish by saying

	cat ../a.java

~/ refers to the user home directory

Using History

history shows list of previous shell commands used. It gave following output on my computer:

 5673  ssh -Y akarki15@romulus.amherst.edu
 5674  cd Desktop/jam/blog/
 5675  jekyll build
 5676  jekyll serve

Run a certain numbered command by !<number of the command>. For exmaple !5676 will run jekyll serve.

.cshrc file

~/.cshrc contains shell configuration
PATH contains paths for programs you run on terminal. E.g. more, less etc

Random cool monitors

top shows the running processes on the system
vmstat 5 shows the paging history, 5 denotes how fast the list is being refreshed
ps uax shows the processes running right now

All about that stream

Three I/O streams of unix (Similar to what it is in Java)
- Say you have a java executable called prog.class
- stdin
  - java prog < inputFile will use inputFile for keyboardinput expected by stdin in java.
- stdout
  - java prog > outfile writes whatever System.out.println("") into the outfile
    - Note that System.err.println("") is written on the screen instead of file
  - java prog >& oufile will write both stdout and stderr into outfile
  - java prog > /dev/tty) >& /path will write stdout to /dev/tty and stderr to /path
  - prog >> outfile appendas to the outfile instead of overwriting it

Pipe command

Feeds the output of one command to another (prog1 to prog2). e.g.

	prog1 < file1 | prog2

Suspend/resume jobs aka COOL STUFF

ctrl+z suspends/pauses the running job
bg puts a job to background
jobs prints the list of jobs
fg %1 bring job no. 1 from background to foreground

grep

grep 'word' filename searches for word in file called filename
grep --color 'data' fileName display grep results in color
grep 'word' file1 file2 file3 searches for word in file1, file2 and file3
grep 'string1 string2' filename searches for string1, string2 in filename
cat otherfile | grep 'something' pipe grep result and display its (their) contents

Tar Tricks

tar cf Simplex.tar Simplex
- create a file Simplex.tar from Simplex
mkdir newDir ; cd newDir ; tar xf ../Simplex.tar
- Creates newDir and extracts Simplex into newDir
Loop: basename parses out from every $i just its filename. The loop creates a copy of every file but changes the extension to .save.

foreach i (*.txt)
	foreach? cp $i `basename $i .txt`.save
	foreach? end