MINIMUM LINUX INTRODUCTION FOR USERS 
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[R.Sonnenfeld - NMT Physics - August 2007]
     
     1	sh-3.2$ #Sometimes you can forget what machine you are on!
     2	sh-3.2$ hostname
     3	speare4b-3-4
     4	#Sometimes you can forget who you are!
     5	sh-3.2$ whoami
     6	rsonnenf
       
    10	sh-3.2$ #Directories are arranged as trees with "/" as the "root".
    11	sh-3.2$ cd / 
    12	sh-3.2$ tree -L 2 |more 
    13	sh-3.2$ #Actually the tree is upside down!  
       
    14	sh-3.2$ #You often forget where you are!
    15	sh-3.2$ pwd  #pwd -- present working directory
    16	/u/rsonnenf
       
    17	sh-3.2$ #Change to a new directory
    18	sh-3.2$ cd phys241  #cd -- change directory
    19	sh-3.2$ pwd 
    20	/u/rsonnenf/phys241 
       
    21	sh-3.2$ #Go back up one level
    22	sh-3.2$ cd ..   # .. mean go up one level
    23	sh-3.2$ pwd 
    24	/u/rsonnenf
       
    25	sh-3.2$ #Go back down
    26	sh-3.2$ cd /phys241
    27	bash: cd: /phys241: No such file or directory
       
    28	sh-3.2$ # OOPS! -- /phys241 means a directory off of root.
    29	sh-3.2$ # This works -- it's the full path name. 
    30	sh-3.2$ cd /u/rsonnenf/phys241
    31	sh-3.2$ pwd 
    32	/u/rsonnenf/phys241 
    
    32a   which matlab -- finding a command
    32b   cd -   Go back where you were last
       
    33	sh-3.2$ #list files (ls)
    34	sh-3.2$ ls 
    35	lectures  linuxintro.txt  matlab  mysteryfile  test.m
    36	sh-3.2$ mkdir newdirectory 
    37	sh-3.1$ ls
    38	lectures  linuxintro.txt  matlab  mysteryfile  newdirectory  test.m
    39	sh-3.2$ ls -l #list files with the "long" option -- more info.
    40	total 24
    41	drwxr-sr-x 2 rsonnenf 1612 4096 Aug 22 18:35 lectures
    42	-rw-r--r-- 1 rsonnenf 1612 6785 Aug 22 18:37 linuxintro.txt
    43	drwxrwx--- 9 rsonnenf 1612 4096 Aug 20 19:02 matlab
    44	-rw-rw---- 1 rsonnenf 1612    0 Aug 23 07:04 mysteryfile
    45	drwxr-sr-x 2 rsonnenf 1612 4096 Aug 22 18:19 newdirectory
    46	-rw-rw---- 1 rsonnenf 1612    3 Aug 23 07:03 test.m
    47	sh-3.2$ Recognize the directories because they have a "d" in front.
       
    48	sh-3.1$ #cp -- The copy command  cp inputfile outputfile
    49	sh-3.1$ #cp is used on your machine only
    50	sh-3.1$ cp linuxintro.txt mysteryfile
    51	cp: overwrite `mysteryfile'? y
     
    52    #Moving files to remote machines:
    53    gftp &
    54    #Type in the host name and your password
    55    #Choose the "SSH" or "SFTP" protocol rather than FTP

    69	#Logging into remote machines -- ssh (secure shell)
    70	-bash-3.1$ ssh richard@feynman.nmt.edu   
       
    72	#General command syntax --
    73	# command -options inputfile (if any) outputfile (if any)
    74	# To look up a command, use "man"
       
    75	#Finally -- we talk about editors.  Choose pico or vim.
    76	# If you choose "vim", run "vimtutor" to learn it.
    77	# Also -- "The easy way" -- gftp --
    78	# Seeing what is in a file -- "more".
    79	# MORE HELP
    80	#http://www.physics.nmt.edu/~rsonnenf/computerlab/computers.html
    81
    82    #Can't resist showing a script --
    83    $ more dateloop.scr
    #!/bin/bash
    # This shows off how to do a command forever while waiting for something to happen

    until [ 1 = 0 ]
    do
            date -u +'%D  %H:%M:%S.%NZ'
	          sleep 0.01
    done
    exit 0

THE POWER OF LINUX
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[R.Sonnenfeld - NMT Physics - August 2012]
Linux comes with lots of power tools.  Can operate on giant
data files easily.

cat data.txt -- "cat" = concatanate
cat data.txt data.txt data.txt data.txt data.txt > big.txt
cat big.txt big.txt big.txt > bigger.txt
sort bigger.txt
head -n 10 bigger.txt
tail -n 10 bigger.txt
wc bigger.txt
grep 107.1345 bigger.txt
# A script to change all occurrences of joe to mary in a file
#!/bin/bash
echo Takes a script called $1.sh and creates $1.shh
echo USAGE: sedit.sh discard_list
sed -e 's/joe/mary/g' $1.sh > $1.shh 

Sort by size
cd ~; ls -lhSR |less

Sort by time
cd ~; ls -lhtR |grep Oct |less

rename 's/ /_/' *   #Uses perl rename facility  Replace the first
#space in each file name with an _

# A script to compress entire directories of photos.
#!/bin/bash
#Not clever enough to recurse to subdirectories. Must do one directory at a time.
#Example Usage:
#richard@elrond:~/photos/2009/Europe$ directory_compress.scr London
#
input_file_directory=$1
rootdir=$(pwd)
echo using ImageMagick to resize and change size on directory $input_file_directory from root $rootdir
output_file_path=$rootdir/$input_file_directory/compressed
mkdir $output_file_path
echo Placing files in  $output_file_path
cd $rootdir/$input_file_directory
 rename 's/.JPG/.jpg/' *   #Uses perl rename facility  Replace .JPG with .jpg
#Program is not clever enough to handle both .JPG and .jpg extensions.

for file in `ls *.jpg` ; do
echo converting $file
convert "$file" -resize 22% $output_file_path/c_$file
#convert "$file" -resize 1024x768 $output_file_path/c_$file
done