Versions, vendors, vser groups, standards

• IBM AIX,
• HP-UX,
• Sun Solaris, (previously SunOS)
• Cray Unicos,
• SGI Irix,
• DEC Ultrix,
• Digital Unix,
• Micro$oft/SCO/Novell Xenix/UnixWare ??,
• OSF/1,
• Linux (open source for x86 PC, Alpha, MIPS, PowerPC, 680x0, all 4 of IBM platforms: i, x, z, p Series.),
  world's largest database at CERN.
  
• *BSD*: OpenBSD, FreeBSD (fast), netBSD (secure), BSDi. Macintosh OS X ("Darwin") is a FreeBSD.

Layers (concentric circles) of Unix: [hardware], kernel, utilities, shell , user.

Varieties of running Linux:

Varieties of experiencing Linux:

X Window

1. setup the graphical display (resolution, color depth, refresh rate) video driver.
2. display windows
3. track mouse and KBD activity

xlsfonts    list of installed fonts
xfd -fn     font viewer
showrgb     list of colornames
xterm      terminal emulator
xf86cfg
xf86config
xvidtune    
startx initx  .xinitrc

lsb_release -a   #distro
uname -a   # lists name and version of operating system, architecture (CPU), IPC
arch      # architecture of system
hostname   # name of system    -i shows IP address
SuperProbe        # video card and its memory.  Linux
dmesg     # boot messages.  Linux.  hardware detected and drivers.
df     # filesystem(s) size.  -i shows inodes. -h human -T type
free      # how much memory 
top       # shows RAM
/proc/version
/proc/cpuinfo      # CPU type and current speed, cache size, BogoMips
/proc/interrupts   # IRQs and # of interrupts
/proc/partitions
/proc/swaps
/proc/ioports
/proc/devices    #files that have IRQs and other device parameters

GUI admin tools:
control-panel  Linux configuration: users, networking, printer, filesystem
linuxconf      admin configuration tool
webmin         web-based admin
system-config-*

Users.
who -i    # who's logged on, idle or active.  -l shows from where.
finger    # who's logged on
finger joe@camel.com   #over network, if camel.com runs finger server.
w      # who's logged on.  Login time, from what remote host, idle time, running what command now, how much CPU time its taken (PCPU), how much total CPU time has used (JCPU).
last      # previous logins of users
lastlog   #last login of every user
/etc/passwd    #system users
write username      send msg 
talk username       chat

System state.
times     #bash builtin.  amount of CPU time used by shell and its processes
ps aux # processes in system: all users, in user format, also processes without terminal x
        $ -ef on SVR4
xload     # "load" of system: some combination of CPU and memory usage
xcpustate  # instantaneous percentage of CPU and memory usage, by categories
xsysinfo  #same info
xmeter    # various monitors (not in Linux?)  perfmeter
xosview
ifconfig      #network packets statistics
iwconfig      #wireless network packets statistics
netstat       #network connections.  -l listening ports. -t tcp statuses.
netstat -l    #ports being listened on
netstat -t    #active TCP ports
nmap          #port scanner
top        # Load average (average number of processes, i.e multitasking)
        # States of all processes: running, sleeping, stopped, undead
        # CPU usage: %user, %system, %idle
        # Memory: total , free, used, shared, buffers usage
        # Swap: total, free, used
        # per process information like in ps:  
        SIZE: virtual memory in KB
        RSS: % of physical memory
        %CPU
        WCHAN: system call sleeping on
        PAGEIN: #page faults

**********************************

Intro to commands:

pwd      present working directory.  where you're "at"
cd dirname       change present working directory to dirname
cd                change to home directory    
cd -              change to previous directory
ls       directory listing
ls -l      long listing gives more info about files
ls -a      show "dot" files, those that start with .
cat fn      display file 'fn'     
                Output can be paused with ^S, resumed with ^Q (on a
                slow terminal, or fumbled fingers) -n line numbers
more fn         display file 'fn' a page at a time.  
            Also: pg and less, head and tail
lpr fn       print file (or lp). to default printer. image and Postscript too.
rm fn        delete fn.  No recycle trash can.
rm f1 f2        delete f1 and f2
cp oldf newf     make a copy of oldf as newf
cp f1 f2 f3 dirname     copy f1, f2 and f3 to directory dirname
cp f1 .                 copy file to this directory
mv oldf targetf  move/rename oldf as targetf
mv oldf dir          move file into another directory
mv dir1 dir2         rename directory or move directory to be a subdirectory of another
mkdir dirname    make a directory
rmdir dirname    delete a directory (must be empty first)

wc fn            number of chars (bytes), "words", lines in fn -L longest line
sort fn          sort fn
grep word fn     search for word in fn
od -c fn         display ASCII chars of fn
file fn          what kind of file, e.g. C source code, executable
                 file, text file, shell script...
locate string         show all files in system that have string as part of name
find -name fn        search for file(s) in disk tree
who          who is logged on, on which terminals, doing what...
ps               what processes you have running in this shell.  Also, others'
                 processes  -e or -u user
ps ux                   all your processes in system, including x not
                           associated with this shell
ps aux                  all processes in system
kill pid     terminate a process
diff f1 f2       differences between f1 and f2
mail         send/receive mail:  Also mailx, elm, pine, mutt, GUI mailers etc.
vi           text editor
emacs        text editor. 
      Other editors: joe, jed, pico, xedit, kedit, gedit, kate (source code aware), kwrite
      Word processors: kword, abiword, wordperfect, openoffice writer
mdir a:             mtools to access FAT diskette
mcopy -t fil1 a:    copy file to floppy
mcopy -t a:fil2     copy from floppy
gcc prog1.c       C compiler.   executable in a.out
g++ prog1.cpp     C++ compiler
javac Hello.java  Java compiler
java Hello        JVM
php, perl, awk, python, ruby, f77 compilers/interpreters
File manager/browser: mc, nautilus, konqueror

$ apropos string # search all the synopses for cmds with the string
$ whatis word
man intro #intro to Linux and shell

Unix Programmer's Manual (about 6 feet wide) had descriptions of how to use the utilities.

-h or --help option
bash help on its built-in commands

GNU info documentation on utilities /usr/info

HOWTOs and FAQs: /usr/share/doc
Linux Documentation Project: linuxdoc.org
comp.os.Linux newsgroup
www.ssc.com/lg Linux Journal
Linux Magazine
Major utilities and distros have their own web sites: samba, apache, gimp, perl, sendmail, xfree86, gnu, gnome, kde, openoffice, applix, etc.
sourceforge.net has tons of the smaller open source projects.
Linux related web sites: end with .com or .org:
starting with "linux" or "li":
today mall links base now central app -center world

***************************************

Categories of commands:
 Output of entire files::             cat tac nl od
 Formatting file contents::           fmt pr fold
 Output of parts of files::           head tail split csplit
 Summarizing files::                  wc sum cksum md5sum
 Operating on sorted files::          sort uniq comm ptx tsort
 Operating on fields within a line::  cut paste join
 Operating on characters::            tr expand unexpand
 Directory listing::                  ls dir vdir dircolors
 Basic operations::                   cp dd install mv rm shred
 Special file types::                 ln mkdir rmdir mkfifo mknod
 Changing file attributes::           chgrp chmod chown touch
 Disk usage::                         df du stat sync
 Printing text::                      echo printf yes
 Conditions::                         false true test expr
 Redirection::                        tee
 File name manipulation::             dirname basename pathchk
 Working context::                    pwd stty printenv tty
 User information::                   id logname whoami groups users who
 System context::                     date uname hostname
 Modified command invocation::        chroot env nice nohup su
 Process control::                    kill
 Delaying::                           sleep
 Numeric operations::                 factor seq

In detail:

Output of entire files
 cat               Concatenate and write files.
 tac               Concatenate and write files in reverse.
 nl                Number lines and write files.
 od                Write files in octal or other formats.

Formatting file contents
 fmt               Reformat paragraph text.
 pr                Paginate or columnate files for printing.
 fold              Wrap input lines to fit in specified width.

Output of parts of files
 head              Output the first part of files.
 tail              Output the last part of files.
 split             Split a file into fixed-size pieces.
 csplit            Split a file into context-determined pieces.

Summarizing files
 wc                Print newline, word, and byte counts.
 sum               Print checksum and block counts.
 cksum             Print CRC checksum and byte counts.
 md5sum            Print or check message-digests.

Operating on sorted files
 sort              Sort text files.
 uniq              Uniquify files.
 comm              Compare two sorted files line by line.
 ptx               Produce a permuted index of file contents.
 tsort             Topological sort.

Operating on fields within a line
 cut               Print selected parts of lines.
 paste             Merge lines of files.
 join              Join lines on a common field.

Operating on characters
 tr                Translate, squeeze, and/or delete characters.
 expand            Convert tabs to spaces.
 unexpand          Convert spaces to tabs.

Directory listing
 ls                List directory contents
 dir               Briefly list directory contents
 vdir              Verbosely list directory contents
 dircolors         Color setup for `ls'

Basic operations
 cp                Copy files and directories
 dd                Convert and copy a file
 install           Copy files and set attributes
 mv                Move (rename) files
 rm                Remove files or directories
 shred             Remove files more securely

Special file types
 link              Make a hard link via the link syscall
 ln                Make links between files
 mkdir             Make directories
 mkfifo            Make FIFOs (named pipes)
 mknod             Make block or character special files
 readlink          Print the referent of a symbolic link
 rmdir             Remove empty directories
 unlink            Remove files via unlink syscall

Changing file attributes
 chown             Change file owner and group
 chgrp             Change group ownership
 chmod             Change access permissions
 touch             Change file timestamps

Disk usage
 df                Report file system disk space usage
 du                Estimate file space usage
 stat              Report file or file system status
 sync              Synchronize data on disk with memory

Printing text
 echo              Print a line of text
 printf            Format and print data
 yes               Print a string until interrupted

Conditions
 false               Do nothing, unsuccessfully
 true                Do nothing, successfully
 test                Check file types and compare values
 expr                Evaluate expressions

Redirection
 tee                Redirect output to multiple files

File name manipulation
 basename           Strip directory and suffix from a file name
 dirname            Strip non-directory suffix from a file name
 pathchk            Check file name portability

Working context
 pwd                Print working directory
 stty               Print or change terminal characteristics
 printenv           Print all or some environment variables
 tty                Print file name of terminal on standard input

User information
 id                 Print user identity
 logname            Print current login name
 whoami             Print effective user ID
 groups             Print group names a user is in
 users              Print login names of users currently logged in
 who                Print who is currently logged in

System context
 date               Print or set system date and time
 uname              Print system information
 hostname           Print or set system name
 hostid             Print numeric host identifier.

Modified command invocation
 chroot             Run a command with a different root directory
 env                Run a command in a modified environment
 nice               Run a command with modified niceness
 nohup              Run a command immune to hangups
 su                 Run a command with substitute user and group ID

Process control
 kill               Sending a signal to processes.

Delaying
 sleep              Delay for a specified time

Numeric operations
 factor             Print prime factors
 seq                Print numeric sequences

    date
    who
    ls

  ls -l
  cp fromfile tofile
  grep word filename
  who am i
  nxterm -geometry 85x30+0+0 -fn 9x15bold -fg white -bg black -cr red &

  ls -l
  ls -t
  ls -l -t
  ls -lt

  lpr -Pprinter4 fn

 rm -i          interactively delete
 grep -i            ignore case in search

System admin:

Install software

RPM: RedHat Package Management

-qa          #list of all installed packages
--querytags  #  All possble info
-qa --qf "%{NAME} %{SIZE}\n"   #  Name and size of all packages

-qi package        #Info about this package
-qR  package       #what it requires
-qip package.rpm   #Info about this package in its file
-ql package        #All files of this package
-qf path-to-file   #what package this file belongs to

rpm -i arfarf-1.0-2.i586.rpm
installs the arfarf package of executable binaries, libraries,
documentation etc.
--force --nodeps  --test
-U package    #upgrade

-V package    #verify it's all there 
-e package    #uninstall (erase) it

/var/lib/rpm/  DB files

Desktop has  GUIs for software install.

yum does automatic download/update of RPMs.

rpmfind.net to 'find' 'RPM's on the 'net'

Debian Package Management

dpkg

-l              #list all packages
-L package      #files of package.   includes all directories in
path??
-s package      #status
--print-avail package  #status
-S path-to-file #which package it belongs to
-I package.deb  #info about package file
-c package.deb  #files in the package file
-r package      #remove package (except config files)
  --purge package 


/var/lib/dpkg
   available
   status

tarball: some software is distributed as "tarball", a compressed tar archive of source code files etc.
5 commands to unpack, compile, install:
1. tar -xzf tarballfilename.tar.gz #or .tgz Uncompress, Unpack. creates a subdirectory.
2. cd tarballdirectory
3. ./configure    #Generate customized makefile for the system.
4. make    #Compile using that makefile.
5. make install    #As root, install onto system.

 x      delete character
 dd     delete line
 :wq    save changes and exit  : means an ed command
 :q!    quit, do not save changes
 i  go into input mode (insert)
 a  go into input mode (append)
 o  go into input mode (open new line)
If arrow keys don't move cursor: h i j k do.

:$      goto end of file
:r fil1     import file
:j      join two lines together
#yy     yank # lines to buffer
p       paste buffer contents
^f      ctrl f  scroll forward page
^b      scroll back

emacs
the ne plus ultra of editors.
GUI, X-enabled
emacs -nw to run in an xterm
source code formatting "IDE"
extensible (has built-in Lisp system for creating commands, binding to keystrokes)
email reader, ange-ftp, news reader, file manager, run a shell inside emacs.
Always in input mode. Menu-driven commands (icons in xemacs), or keyboard are issued by holding Control or Alt.
Cursor movement by arrow keys, Home, End, Page Up, Page Down.
But if those keys don't work on your system (it's configurable):

up line      ^P  (means holding Ctrl, press lowercase p)
down line    ^N
beginning  line  ^A
end of line  ^E
down page    ^V
up page M-V   (means holding Alt, press lowercase v)
              M is 'meta' (emacs jargon). Might be press and release
             Esc on some sYstems.
Deleting text:
char        ^D or maybe Delete.  Backspace deletes char to left of
             cursor
line        ^K
word        M-D 

Save changes     ^XS  holding Control, press x then s
Quit         ^XC
Load a file  ^XF  will be prompted for name of file
Insert a file   ^X i  (means do ^X followed by i, without holding ctrl)
Undo         ^X u
Cancel       ^G  to stop some inadvertant command
reformat paragraph   M-Q
switch to other buffer  ^X b
one buffer only         ^X 1

  ? list of commands
  h list of messages, * is current message
  n display message #n
  r respond to current message
  d delete current message

bash Ease of use features

^A  beginning of line   Home key.
^E  end of line.            End key
^D  delete char.  Or Backspace to delete previous char.  Delete key.
^K  delete to end of line
^U  kill line (actually kernel)
Esc D  (or Alt D) delete word
!54  re-execute command #54
!la   re-execute most recent command that started with la

h     history
lo    locate
j     jobs
cp    cp -i
mv    mv -i
m     more
g++   g++ -Wall -ansi

l() {
  ls -l $* | more
}

usage() {
  echo "Usage: et [-a name number | -d name | -p | name]"
  exit $1
}

e() {
  emacs -fg white -font 9x15bold -geometry 90x30+0+0 $* &
}

calc() {
  echo "$*" | bc -l
}

Your terminal

$ stty erase '#'      [quoting necessary?]
Change back to backspace char:
$ stty erase ' '   Backspace was pressed between the quotes, but since it doesn't have its  special meaning of delete anymore, it's just another character. Now BS is the erase char again.
$ stty erase ^h  Also set erase to backspace char.
$ stty -a         Shows signal mapping.  Can change interrupt, EOF, kill, word erase

echo aBSm | od -c                 # m         
echo a\BSm | od -c               # a \b m    Escaping the erase char

^S pause
^Q resume

Shell: benefits

Filename generation: (globbing) match existing filenames

  *  match any string of chars, including null string.
  ?  match any single char.        * and ? are called wildcards.
 []  match any one of the chars enclosed.  A pair of chars,
  separated by a minus will match any char in ASCII order. [abc] [a-z]
  [!]  or [^] match any char except one of the enclosed. [^a-z]

*     all files
f*    all files in current directory that start with f, including f
*f    all files that end with f, incl. f
f?*   all files in current directory that start with f and have at
         least one other char
[a-z]*        start with a thru z
[a-z]         single lowercase letter filenames
f[aeiou]?  start with f, followed by a vowel, followed by one char
*.gif          all files ending in .gif
*.???         all files ending in a DOS-like extension
/etc/rc5.d/S*  files in that directory that start with S

$ ls -l *.cpp           #files that end in .cpp
$ grep rand *.cpp   #search for rand in all C++ programs
$ ls -l [a-z]*[0-9] #lists files that start with lower letter, end with digit, anything, or nothing, between.
$ rm *[0-9][0-9]    #deletes all files whose names end in two digits

$ rm *[10-99]       Warning: shell doesn't know numbers.  This is not ten thru ninety-nine.  1 or 0 thru 9 or 9 (poorly written, is equivalent to [0-9]).   ASCII sequence only.
[1-9][0-9]

$ rm * [0-9][0-9]       
Warning: space after *, will match all files and delete them all!

$ cp /home/billybob/file1 .       #copy into current directory
$ cd ..          # move up a directory
$ cp ../file .    #copy file in parent directory to this directory
$ mv ../*.h .  #move the .h files from parent directory to this one
$ mv *.h ..        #move them back up

$ echo hello world
hello world
$ echo hello           world      #2 arguments
hello world
$ echo f*                # shell expands to list of all matching files
f1 fil2 fred.c         # all the filenames that start with f 
$ echo *                # all filenames
f1 fil2 fred.c mystuff junk 
$ echo *[0-9][0-9]
$ echo asdfasdf >afile

$ echo f*5
f*5
$ echo *     #in an empty directory
*

User command line   After shell processing
    ls f*       ls f1 fil2 fred.c
    f*      f1 fil2 fred.c   
                      (probably error, would try to execute command f1)

1. keywords (if, case, for, function, while, !, {} ...)
2. aliases
3. built-in commands (alias, cd, echo, export, history, jobs, kill, read, set, shift, test, trap, umask ...)
4. functions
5. PATH search for command

• noclobber can't redirect to existing file
• ignoreeof can't ^D logout
• emacs using emacs editing mode
• trackall

$ cat f1 >f2         # copy f1 to f2
$ cat f3 >>f2     # append f3 onto f2
$ cat <f1            # display f1
$ cat f1 f2 f3 >f4   # all to f4
$ cat f1 f2 f3 >>f4   # all appended to f4
$ cat f1 >dir1       # ERROR.
$ mail billybob <letter3 # letter3 is the message
$ cat f1 >f1         # wipes out f1
$ cat <f1 >f1     # Warning.  creation of f1 wipes out contents
$ cat f1 f2 >f2      # net result is copy of f1 in f2
$ cat f1 >>f1 # not allowed: won't append f1 to itself  
                [if f1 not exist creates empty]
$ cat <f1 >>f1     # not allowed.  recurses?!
$cat f* >f5
$ sort xfile >xfilesorted   
$ grep math *.cpp >mf   #all lines containing 'math' from all the 
                    C++ files into file mf
$ file * >filetypes     #type of all files

 cat f1     filename argument
 cat <f1 redirect input so comes from file f1, cat command does 
        not see redirection. No file argument for cat command here.
 cat >f2     output redirected to file f2.  No file arg to cat.
  What's the input? Keyboard or mouse paste.  Will accept input until ^D.

$ >f2 cat<f1
$ cat <f1 <f3       # second < overrides first <

$ ls >f2     # directory listing will contain f2
$ ls -l >f2      # f2 as empty 
$ >f3        # f3 created, empty.  No command executed.

$ cat f1 - f2 >>fx          # from f1, then standard input, then f2

$ cat f1 /dev/stdin f2 >> fx

Piping:

$ who >temp      #temporary file to hold output of who
$ sort temp      

$ who | sort             | is the pipe operator.  creates a pipeline

$ ls -l | more      #page at a time directory listing
$ ls | wc -l

$ ps ax | wc -l
$ ps -aux | grep billybob | wc -l #number of processes billybob has
$ file /usr/bin/* | grep script      #which cmds in /usr/bin are scripts
$ cut -d: -f1 /etc/passwd | sort | more    #sorted list of usernames
$ wc * | tail -1

who | sort | lpr
(who | sort) | lpr
lpr (who | sort)

cat >f1 | cat
cat <f1 | cat >>f1

  terminal (default)|                      |  terminal (default)
      or          
  file  <fn         | stdin COMMAND stdout |  file  > or >>
     or           
  pipe  |           |                      |  pipe   |

Processes.

$ ps
PID    TTY     STAT  TIME   COMMAND
2168   u05     S        0:03    bash
2263   u05     R     0:00     ps

ps -e   all processes in system.     or aux
ps -f   more info: when started, parent process PPID
ps -l   more info: priority, memory used, state

$ sort bigfile | lpr & #entire pipeline run in background.  | higher precedence than & 

$ date; who ;pr fn 

$ for i in `cat classlist` ;do mkdir $i ;done
syntax requires that do and done must be at start of line

$ (sleep 300; echo Wake up) &    # catnap for 5 mins.   
                    & higher precedence than ; so need parens

Subshell spawned.
(date;cat f1) | lpr

$ at time command        Runs the command at the specified time.
                       E.g. start it at midnight 
$ at -f script-file 4 am friday
$ at -l         # list my at jobs
$ at -r id      # remove an at job

$ date
Tue  12 Apr  12:20  1995
$ echo date
date
$ echo `date`
Tue  12 Apr  12:21  1995
$ echo Today is `date`
Today is Tue  12 Apr  12:21  1995
$ `date`       is replaced by its output, attempt is made to execute
Tue: command not found


$ ls -l `which cat`    
#long listing of the cat command file, wherever it is

Useful to give list of filenames to command:

$ wc `locate .java | grep wills`  #wc of wills' .java files

$ ls -l `find . -name 'core*'`  # listing of all core dump files

$ file `locate .gif` | egrep -v 'GIF|symbolic'  
#any .gif filename that is not a GIF file nor a symbolic link

Which bash builtins are also the name of commands in your PATH of directories?
$ for i in `cat bash_builtins` ;do which $i 2>/dev/null ;done

$ mail billybob barack hillary rudy mitt <letter1
$ cat >tolist
billybob
barack
hillary
rudy
mitt
$ mail `cat tolist` <letter1

$ cat  alf
a
b
c
d
$ echo `cat alf`                # echo turns newline into space
a b c d

$ ps -aux | fgrep "`who | cut -f1 -d' '`"    
#processes of logged on users

                Output
 echo *         all filenames
 echo \*        * 
 echo \x        x 
 echo \*\?      *?
 echo \\        escape the escape char, so \  is echoed
 echo ab\BScd   escape the backspace char.  acd on terminal, 
                but ab\bcd
 echo ab\BSBScd backspace over the escaped backspace.  
                abcd on terminal
 echo \BS       is \b
(Pipe these into od -c to see the chars:  \b is backspace).

                Output
echo '*'        *
echo '*?'       *?
echo '\*\\'     \*\\
echo 'hello'    hello
echo hi   bob   hi bob            #two args to echo
echo 'hi   bob' hi   bob      #one arg to echo
echo 'abBScd'   acd   Kernel does erase processing
echo 'ab\BScd'  echoes acd, but is ab\bcd   Kernel-escaped the erase

$ echo 'hello
>world'
hello
world
$ echo hello\   #\ at end of line means continued on next line.  newline effectively ignored.
>world
helloworld
$

Try echoing:
\$   
\\$   
\\\$                     \$
'\$'
'\'$   
'\'$'   
\\  
\\\                       secondary prompt 
\\\\                       \
\\ \\                      \ \
\\\\\\                      \\

$ echo -e 'hello\b wor\nld \t stuff\c'  # quote to protect from shell
hell wor
ld  stuff$

$ echo -e                   #to enable the escape sequences
$ echo -n hello world       #suppress newline

File creation.

$ ls -i      # shows inode numbers of files
$ df -i     # inodes per filesystem 

Linking:

dangling link: blinks red

Hard links make filesystem a DAG (directed acyclic graph). Soft links can make it a graph (eg. cycle if link to an ancestor directory).
*************

File security

Shell variables

$ pet=bulldog
$ echo pet
pet
$ echo $pet     # $ is metacharacter to access value of shell variable
bulldog
$ echo \$pet    # escape the $
$pet

$ set        # display all variables        
                 env shows exported variables
. 
HOME        pathname of home dir
PWD         current directory
DISPLAY     X terminal address
TERM        terminal type
PATH        search path.  list of directories shell will 
                search to find command.  an empty : is current directory.
PS1          prompt: \h host, \u username, \s shell, \W pwd, \d date,
             \t time, \! cmd #, \007 bell,
             \[  \] terminal control sequence within
PS2          secondary prompt
SECONDS     since login
RANDOM      random integer, changes each use
pet             User defined variable

$ echo $HOME
/home/billybob

$ sh       # create a child shell process. Linux: sh is bash
$                 # are now in that shell
Picture....

user-defined shell variables are not passed to child shells!
$ x=Hello
$ echo $x
Hello
$ sh                 # spawn child shell
$ echo $x            # it doesn't have x

$ exit             # or Ctrl-d  to terminate this shell.  Ctrl-d is end-of-input signal.
$ echo $x       # Now back in original shell
Hello

$ x=Hello
$ export x
$ sh 
$ echo $x
Hello
$ x=Bye
$ echo $x
Bye
$ sh                   # grandchild 
$ echo $x
Hello       # the originally exported value.   
            ksh exports newer value, i.e. bye
$ ctrl-d             # back to child
$ export x
$ sh                   # (another) grandchild
$ echo $x
Bye
$ crtl-d
$ ctrl-d
$ echo $x
Hello

unset to delete a variable
$ unset x

echo Date and time is:
date

$ sh simp1
Date and time is:
Mon 23 Feb 15:32   1996
$

$ sh <simp1
Date and time is:
Mon 23 Feb 15:33  1996

$ chmod +x simp1                # make the file executable
                                  or chmod 700 or 755
$ simp1        # execute the commands in it.   simp1 is now a command!
Date and time is:
Mon 23 Feb  15:35  1996

./simp1   to skip PATH

$ #this is a comment
$ echo Hello    #comment here, not an argument of cmd
Hello
$ echo Hello#again      #embedded # is not start of comment
Hello#again

 #hi--says Hello
  echo Hello        # an obvious comment,not really needed
  echo Hello#again  # internal # not the start of comment

$ hi
Hello
Hello#again

 echo What is your name\?
  read name
  echo Welcome, $name

$ welcome
What is your name?
billybob
Welcome, billybob

joe doe     == joe doe
joe     doe     == joe doe
'joe    doe' == joe    doe

 # argtest
  echo Name of script is $0
  echo First arg is $1
  echo There are $# args: $*

$ argtest hi there billybob |wc
  3   16  78


  # snag--make copy of arg file in backup dir
  cp $1 $HOME/snag/$1.sv

$ save coolfile            # cp coolfile /home/billybob/backup/coolfile.sv

$ set  a b c          # set assigns values to positional parameters
$ echo $2 $1
b a

 # wh--what's my username
  set `who am i`
  echo $1

 #wh--what's my name, and where am I
  set `who am i`
  echo You are $1 on terminal $2


  #cx--give x permission on file args
  chmod +x $*

 #runarg--execute the argument
  $1

 #runargs--execute the arguments
  $*

 # gsort--sort lines containing word in file
  grep $1 $2 | sort

 # gsort--sort lines containing word
  grep $1 $* | sort      # WRONG.  $* includes $1, i.e. the word.

 # gsort--sort lines containing word
  word=$1
  shift
  grep $word $* | sort

$ date
Tue 12 Apr 1997  14:23
$ echo $?
0                # 0 is successful "true".  opposite of C.
$ cat f1
cat: cannot open f1
$ echo $?       #[bash always showing 0 ???]
2                              # nonzero is some error (convention). 
       # Different errors have different exit statuses, per  command.
$ cat <f1
f1: cannot open            # from shell. cat not run
$ echo $?
1

$ date >>log &                   # stdout of shell, e.g. terminal.    
4338
$ echo $!
4338
-----------
[???]
$ sh >f         # stdout to file f.  Redirect output of subshell 
            (so output of cmds to f) but get the prompt.  
$ sh >f 2>$1     # no prompt but prompt not in f
---------
$ echo $$
4096
$ ps
PID     TTY         TIME  COMD
4096 ...                               sh
4145 ...                               ps

 # sf
  sort $1 >$1.$$

 #qm--mail a one line message to $1
  #usage: qm username message
  recipient=$1
  shift
  echo $* >temp$$     # args, ie. msg, to file
  mail $recipient <temp$$
  rm temp$$

  #cgo--compile and go
  cc $1 && a.out

$ cgo prog1.c            # a.out executed only if compile is successful

#medics--lookup a doc
#usage: medics name/specialty
grep -i $1 <<tohere
Joe Lenfant  pediatrics
Jane Roe   obstetrics
Richard Dent  dentistry
John Public  family
Davy Jones  pathology
Al Krebs  oncology
Lou Pasteur epidemiology
tohere

'  ' escape special meaning of all enclosed chars.   
         strong quote
$ echo 'take this `~\|!@#$%^&*()?.,><-=+" line literally'
take this `~\|!@#$%^&*()?.,><-=+" line literally

" "    escape special meaning of all enclosed chars except:
        weak quote
    $  variable value
    `  command substitution
    \  escape ($  `  "  newline when in pair of double quotes")

$ echo "take this ~|!@#%^&*()?.,><-=+ line literally"  # no ` \ $
take this ~|!@#%^&*()?.,><-=+ line literally

$ echo "there are `ls|wc -l` files in `pwd`"
there are 37 files in /home/wills/bin

name='John Q. Public'
grep "$name" xfile

$ echo ' "hello" '
 "hello"
$ echo \"hello\"
"hello"
$ echo " 'hello' "
 'hello'
$ echo ""hello""
hello
$ echo "*"hello"*"
*hello*

$ fruit=peach
$ echo "the value of fruit is $fruit"
the value of fruit is peach
$ echo "Today is `date`"
Today is Mon 12 Mar  1996

  # wh--what's my name
  set `who am i`
  echo $1
$ wh
billybob
$ echo `wh`
billybob
$ echo '`wh` is a good student'
`wh` is a good student
$ echo "`wh` is a good student"
billybob is a good student

$ repeat five
five
$ repeat five gold rings
five
$ repeat 'five gold rings'
five gold rings
$ repeat 'five                 shell expects matching end quote
>gold rings'                         > is secondary prompt PS2
five gold rings
$ echo 'five
>gold'
five
gold
$
  #repeat--echo arg
  echo "$1"
$ repeat five
five
$ repeat 'five gold rings'
five gold rings
$ repeat 'five
>gold rings'
five
gold rings
$

... | tee file | ...
... | tee /dev/tty | ...                 # to terminal

 # fortest
  for i in Unix is great
  do
    echo $i
  done

 for i in *
  do
     cmds...
  done

  for i in $*
  do
    cmds...
  done

 #fpeek--first line of file args
  for i in $*
  do
    echo -e "$i : \c"
    head -1 $i
  done

 # mlet--mail file first arg to other args users.  Log file.
  #Usage: mlet filename username(s)
  letter=$1
  shift
  for person in $*
  do
    mail $person <$letter
    echo $letter sent to $person on `date` >> $HOME/.letlog
  done

---------
 # fortest
  for i in a*      # shell running the script expands the *
  do
    echo $i
  done

 # fortest
  for i in 'a*'     #  escape filename expansion.  loops once 
  do
    echo $i         # echo a*, expanded to filenames.  Arg to echo.
  done

 for i in 'a*'
  do
    echo "$i"        # echo "a*"
  done

 # menu--present simple menu, read choice, do it
  echo Choose number to do.
  echo '1 date      2 who'
  echo '3 ls        4 pwd'
  read choice
  case $choice in
  1) date;;
  2) who;;
  3) ls;;
  4) pwd;;
  *) echo Invalid choice;;    # catchall, matches any string
  esac

$ menu
Choose number to do.
1 date       2 who
3 ls           4 pwd
4                                              # user's input
/usr/umad/billybob/testdir
$

 #movestuff
  for file in *
  do
    case $file in
     *.old) rm $file
            echo Deleted $file;;
     *.c|*.f) mv $file $HOME/source/$file
              echo moved $file;;
    esac
  done

Alternative patterns:
*.[cf]
*.?

 # grit-- grep and quit when word not found in file
  # Usage: grit word file(s)
  word=$1
  shift
  while grep $word $1 >/dev/null  #throw away any output of grep
  do
    shift
  done
  echo First file not containing $word is $1

 # isdone--report when file is created
  # Usage: isdone filename
  until find $1 >/dev/null
  do
    sleep 30
  done
  echo ^Gfile $1 is here now

 # clean--remove a duplicate file
  # Usage: clean file1 file2
  if cmp $1 $2 >/dev/null      # cmp has exit status 0 if files are same contents
  then
    rm $2
    echo $2 was a duplicate and has been deleted
  fi

if date | grep Fri
then
  echo Bermudas and hawaiians
else
  echo monkey suit
fi

 #either--finds if word is in either file args
  #Usage: either word file1 file2
  if grep $1 $2 >/dev/null ;then
    echo $1 is in $2
  elif grep $1 $3 >/dev/null ;then
    echo $1 is in $3
  else
    echo $1 is in neither $2 nor $3
  fi

 #grits--report all files not containing word
  #usage: grits word files
  word=$1
  shift
  for i in $*
  do
    if grep $word $i  >/dev/null
    then
      : #placeholder req'd.  : is the do nothing command
    else
      echo $i does not have $word
    fi
  done


! logical not 
if ! grep $word $i >/dev/null
 then
  echo $i does not have $word
fi

test

 # testtest
  echo What is the best OS\?
  read answer
  if test $answer = Unix
  then
    echo Correct!
  else
    echo What\?\?\?
  fi

 [ -n string  ]     # true if non-zero length
 [ -z string  ]     # true if zero length
 [ string  ]        # true if not null string???
 [ string1 = string2 ]
 [ string1 != string2 ]

[ -f file ]      # true if regular file exists
[ -r file ]      # true if file is readable
[ -w file ]     # true if file writable
[ -s file ]     # true if file is not zero length
[ -d file ]     # true if file is a directory

 #testtest2
  if [ -r "$1" ]
  then
    cp $1 $HOME/project
  else
    echo $0: $1 not readable
  fi

 if [ $# -ne 2 ]
  then
    echo Need two arguments! 
    exit 1     #quit and set exit status
  fi

[ 5 = 5 ]       # true
[ 5 = 05 ]          # false
[ 5 -eq 05 ]    # true
[  10 \< 9 ]  #true!
[ 10 -lt 9 ]    #false

[ ! -r myfile ]            # true if myfile is Not readable
[ -r file -a -w file ]     # true if file is readable and is writable
[ -r file -o -w file ]    # true if file is readable or it is writable
[ $answer = Unix -o $answer = UNIX ]
if [ ! -d $dirname ] ;then mkdir $dirname ;fi
if [ ! -r "$1" ] ;then echo "$1" not readable. Bye; exit ;fi

 # clean--remove a duplicate file
  # Usage: clean file1 file2
  if [ "$1" != "$2" ]
  then  
    if cmp $1 $2 >/dev/null    # cmp has exit status 0 if files are same contents
    then
      rm $2
      echo $2 was a duplicate and has been deleted
    fi
  else 
      echo $0: same file  
  fi

  [[ $1 != $2 ]]       safe if the variables don't exist
  [[ $1 < $2 ]]     instead of -lt
  [[ $1 == 5 && $2 == billybob ]]   instead of -a

 # possess--grab a file for me
  # Usage: possess file
  filename=$1
  set `who am i`
  cp $filename $HOME/$filename.$1

 # possess--grab a file for me
  # Usage: possess file
  # check for correct number of args
  case $# in
    1) ;;          #correct number of args
    0) echo Usage: $0 filename  1>&2
       exit 1;;        #terminate script with exit status of 1
    *) echo Warning: only first argument is used  1>&2
  esac
  #check for file existence and copy permission
  if test ! -f $1
  then
    echo $0: file $1 not found  1>&2
    exit 2
  elif test ! -r $1
  then
    echo $0: file $1 not readable 1>&2
    exit 3
  else
    filename=$1
    set `who am i`
    cp $filename $HOME/$filename.$1
  fi

  # mgrep--search file for lines with multiple words
  # Usage: mgrep file word(s)
  file=$1
  shift
  temp1=/tmp/mgrep1.$$  #temp file with unique name in tmp dir
  temp2=/tmp/mgrep2.$$
  for word in $*                  # loop thru word list
  do
    grep $word $file >$temp1
    cp $temp1 $temp2
    file=$temp2                   # search result of last grep
  done
  cat $temp1
  rm $temp1 $temp2              # cleanup the temp files
  exit 0

Signals.

Number  Name           How generated and sent to process
  1     hangup HUP      logout                           SIGHUP
  2     interrupt INT   ^C                               SIGINT
  3     quit            ^\     quit and make core dump
  9     KILL            kill -9 pid                      SIGKILL
 10                                                      SIGUSR1
 15     termination     kill pid                         SIGTERM
 19     stop            ^Z   job control                 SIGSTOP

 # traptest
  trap 'echo Caught signal'  2
  while :
  do
    sleep 10
   done

 # snooze--beeps after $1 seconds
  # Usage: snooze seconds
  sleep $1
  echo ^GWakeup\!        # ASCII 7 (Bell)

 # snooze--beeps after every $1 seconds
  while true  
  do
    sleep $1
    echo ^GAnother $1 seconds have passed
  done

  # snooze--beeps every $1 or 60 seconds

  case $# in

    0) sec=60;;

    1) sec=$1;;

  esac

  while :

  do

    sleep $sec

    echo ^GAnother $sec seconds have passed

  done

$ expr 5 + 6            # spaces around operator needed
11
$ expr 9 - 2
7
$ expr 4 \* 3             # escape *
12
$ expr 10 / 3            # integer division
3
$ expr 10 % 3          # mod
1
$ cows=`expr $legs / 4`

 read i
  while [ $i -gt 0 ]
  do 
    echo $i
    i=`expr $i - 1`    # i = i-1
  done

 read i
  while (( i > 0 ))
  do
    echo $i
    (( i=  i-1 ))
  done

 echo Enter your name
  read name
  until [ "$name" ]
  do
    echo No name given, try again
    read name
  done
  echo Welcome $name

 #move $1 $2  mv files from dir $1 to dir $2, prompt for each
  ls $1 | xargs -i -p mv $1/() $2/()

$ find . -print | xargs file | fgrep " $1" | sed 's/\:\   .*//'
                                                      tab                        tab

Various scripts.

#watchfor--watch for someone to log in
#Usage: watchfor username

case $# in
 0) echo  Usage: $0 user  1>&2; exit 1;;
 1) ;;
 *) echo Warning only first argument used  1>&2;;
esac

until who | grep $1  >/dev/null
do
  sleep 60
done

echo ^G$1 logged on now 1>&2

#watchwho--watch who logs in and out
#Usage: watchwho

new=/tmp/wwho1.$$
old=/tmp/wwho2.$$
>$old                #create the old who listing, empty

while :
do
  who | sort >$new
  diff $old $new
  mv $new $old       # new becomes old for next loop
  sleep 20
done        |   awk '/>/ {$1 = "^Gin:   "; print}
                     /</ {$1 = "^Gout:  "; print}'

# bundle--group files into distribution package
#  Usage: bundle file(s)

echo '# To unbundle, sh this file'
for i in $*
do
  echo "echo $i 1>&2"        
  echo "cat >$i <<'End of $i'" # cat the here doc to file
  cat $i                       # here doc 
  echo "End of $i"
done

# pick--select arguments
# Usage: pick args

for i in $*
do
  echo -e "$i? \c" >/dev/tty    #prompt user at terminal
  read response
  case $response in
   y*) echo $i;;             # to stdout of pick
   q*) break
  esac
done    </dev/tty            #user's input from terminal

$ lp `pick *`
f1? y
myfile? n
new.c? y
prog1.cpp? q
$ pick `cat f1`     #args to pick are contents of f1
$ pick * >f2             #creates list of chosen filenames
$ cp `pick *.txt` Txtfiles/ #copy selected .txt files 
$ lp `pick \`cat f1\``
(contents of f1 as args to pick, thus queries to user)

$ for f in `pick *` ;do mv $f $f.C ;done    
#change name of selected files

#spellchk--check spelling, with user-supplemented file of words
# == spell +file
#Usage: spellchk okwordsfile file

spell $2  |           #output is spell's mispelled words
while read word
do
  if grep -i "^$word\$" $1 >/dev/null  
  then
    :
  else
    echo $word
  fi
done

#find_links--find the links of arg in subtree
#Usage: find_links file [directory]
if [ $# = 1 ]
then
  dir='.'        #default is current dir
else
  dir=$2
fi

file=$1
set -- `ls -l $file`   #get link count
lnkcnt=$2

if [ $lnkcnt = 1 ]
then
  echo $0: no other links 1>&2
  exit 0
fi

set `ls -i $file`    # get inumber
inode=$1

find $dir -inum $inode -print    

#journal--add entries to a journal file
#Usage: journal
file=$HOME/.journal
date >> $file
echo -e "Enter name of person talked to: \c"
read person
echo $person >> $file
echo >> $file
echo "Enter entry: "
cat >> $file
echo ------------------------------------- >> $file
echo >> $file

#sortmerge--sort and then merge two files
#Usage: sortmerge file1 file2
if [[ $# != 2 ]]
then
  print "Usage: $0 file1 file2"
  exit 1
fi
trap 'rm f1.$$ f2.$$; exit 2' 1 2 15
#sort the input files into temp files
sort $1 >f1.$$
sort $2 >f2.$$
#set FDs 3 and 4 to the temp files, so can read from them
exec 3<f1.$$
exec 4<f2.$$
#read a line from each sorted file
read -u3 line1
stat1=$?    #true until at eof
read -u4 line2
stat2=$?
while [[ $stat1 = 0 && $stat2 = 0 ]]
do
  if [[ "$line2" > "$line1" ]]
  then
    print $line1
    read -u3 line1
    stat1=$?
  else
    print $line2
    read -u4 line2
    stat2=$?
  fi
done
#one of the files is at eof, read from both until at eof
while [[ $stat1 = 0 ]]
do
  print $line1
  read -u3 line1
  stat1=$?
done
while [[ $stat2 = 0 ]]
do
  print $line2
  read -u4 line2
  stat2=$?
done
rm f1.$$ f2.$$