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Week 4 Notes for CST8129
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-Ian! D. Allen - idallen@idallen.ca

*** Keep up on your readings (Course Outline: average 5 hours/week homework)

Remember - knowing how to find out an answer is more important than
    memorizing the answer.  Learn to fish!  RTFM!  (Read The Fine Manual)

Reminder: Midterm Test #1 in Week #5 (see the course home page).
  - practice questions and practice test is available under Notes
  - one crib sheet, letter or A4, one side
  - termtest1directions.txt     Directions and preparing for Test #1
  - practiceCommands_1.txt     Practice Unix/Linux Questions #1
  - practiceTest1.*     Practice Test #1 Questions

Review:
    ^C ^D, echo hi | wc
    wc -wc wc >wc   ; ls -ls wc >date
    x='*' ; echo $x ; echo "$x"
    OUTPUT: "You can only redirect what you can see."
    INPUT: "The shell can't force a program to read stdin."
      "Programs that read files, when run without file names, read stdin."
    WRONG: echo /bin | ls, cp foo bar >out, sort <f >f

See Notes file miscellaneous.txt
    Why doesn't backspace always work?
    - command: stty erase ^?
    - command: stty erase ^H
 - learn various ways of getting out of programs
 - don't send binary (executable machine code) files to your screen
   - check the contents with the "file" command first

Man pages (see Notes man_page_RTFM.txt):
 - know how to read man pages (man page syntax meaning)

New commands: tree, sum, cat -n, last, diff -u, stty, cut -d -f, uniq -c
 - See Notes: unix_command_list.txt
 - keep an ongoing list of commands and their common uses
 - keep notes on what the common options do (e.g. "ls -alsd")
 - keep current on the commands covered; look up what you don't know

 - "ls -ld" is needed to see the attributes of a directory
   (instead of seeing the attributes of the directory contents)
   - note that "ls" really means "ls ."
   - note that "ls -d" really means "ls -d ."
 - ls -s shows sizes in blocks (usually 1K blocks on Linux)

 - cut selects fields from input lines
   - head,tail,grep select lines, cut selects "columns"
   - combined, you can select anything from a text file by row and column

Building command pipelines:
 Find the userid that logs in the most?
 Build up a command pipeline slowly, from individual parts:

 $ last
 $ last | cut -d ' ' -f 1
 $ last | cut -d ' ' -f 1 | sort
 $ last | cut -d ' ' -f 1 | sort | uniq -c
 $ last | cut -d ' ' -f 1 | sort | uniq -c | sort -nr
 $ last | cut -d ' ' -f 1 | sort | uniq -c | sort -nr | head -1

Redirect stderr separate from stdin (see Notes redirection.txt):
    1>out vs. 2>out, 2>&1 "send stderr to same place as current stdout"
    ls . nosuch 2>&1 >out  # WRONG
    ls . nosuch >out 2>&1 

Throw away unwanted output to /dev/null 
    $ ls . nosuch 2>/dev/null
    $ cat /etc/* 2>/dev/null >out

Redirect stdin from file, not program (see Notes redirection.txt):
    wc <foo
    - no file name displayed when no file name is given to wc
    - shell opens the file, not wc; wc just reads stdin

Moving around in the file system: . and ..
 - see Notes pathnames.txt     Unix/Linux Pathnames

Notes to review:
    week04notes.txt     Week 4 Notes for CST8129
    man_page_RTFM.txt     Searching for items in the Unix manual pages (RTFM)
    practiceCommands_1.txt     Practice Unix/Linux Questions #1
    practiceTest1.*         Practice Test questions for Test #1
    unix_command_list.txt     Basic Unix/Linux Command List
    miscellaneous.txt     Miscellaneous Unix Facts
    unix_shell.txt     The Unix/Linux Shell
    redirection.txt     Unix Shell I/O Redirection (including Pipes)
    terminal.txt     Using telnet/ssh Terminal emulators
    quotes.txt     Unix/Linux Shell Command Line Quoting
    glob_patterns.txt     GLOB patterns (wildcard pathname matching)

Readings for Week 6:

    shell_variables.txt  Shell Variables you should know (including $* and $@)
    permissions.txt     Unix Permissions

    Quigley: Chapter 2 (Bourne Shell and KSH only - no CSH or TCSH)