User talk:Bossa nesta

Mid-term Note - SPR720

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    File Permission

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$ chmod 7777 rpm.txt ; ll rpm.txt -rwsrwsrwt 1 BossaNesta BossaNesta 41310 2008-10-12 16:39 rpm.txt $ chmod 7000 rpm.txt ; ll rpm.txt ---S--S--T 1 BossaNesta BossaNesta 41310 2008-10-12 16:39 rpm.txt $ chmod 4234 rpm.txt ; ll rpm.txt --wS-wxr-- 1 BossaNesta BossaNesta 41310 2008-10-12 16:39 rpm.txt

> set-user-id (suid)

= use owner ID instead of current user ID

> set-group-id (sgid)

= inherit group ID from directory, 
= sub-dir will automatic has same sgid
= even over sudo command and root ID

> sticky bit

= on old systems, file was not swapped out and stuck in memory
= a file in that directory can be renamed or deleted only by the owner of the file/directory or the superuser. 

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    BASH SCRIPTING

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$ cal 16 2008 2>&1 >all-output.txt run 'cal' with parameter "16 2008", err out to display/terminal, output to "all-output.txt" $ cal 16 2008 2>err.txt >all-output.txt err out to "err.txt", output to file "all-output.txt"

grep "/bin/bash$" /etc/passwd | cut -d: -f1 | sort | mail -s "Bash users" joe@example.com

1. selects all BASH users from the system account file /etc/passwd 2. cuts out the user name ('cut -d: -f1') 3. sorts them into order ('sort') 4. e-mails them to joe@example.com with the subject line "Bash users".

$ vi $(date +%Y)-notes.txt creat a note that start with year, forexample, "2007-note.txt", "2008-note.txt"

$ vi $(date +%Y%m%d)-notes.txt creat a note with current year, month, date, e.g: "20081012-note.txt'

$ vi Nes$(date +%Y%m%d)-notes.txt creat a note with the name started with "Nes" follow by current year, month, date, e.g: "Nes20081012-note.txt'

= single quote is actual value/string, double or no quote is variable

$ X="Test" $ echo "$X" Test $ echo '$X' $X $ echo $X Test

= ALWAYS use double quote for value $ touch "test file" $ NAME="test file" $ rm $NAME rm: cannot remove `test': No such file or directory rm: cannot remove `file': No such file or directory $ rm "$NAME"

= 'export' to turn variables into environment variables, so, all sub process can use the variable(s) $ TEST="Yes" $ bash -c 'echo $TEST'

$ export TEST $ bash -c 'echo $TEST' Yes $

= destory/erase variables unset Var_NAME

Common Environment Variables

Variable ↓ Description ↓ $PATH command search paths $HOME Current user's home directory. $MAIL Current user's mailbox. $DISPLAY X window display specification. $TERM Current terminal type (used to analyze keypresses and send special codes such as colours and effects to the terminal). $SHELL Absolute pathname of the default shell for the current user. $HOSTNAME Name of the host (computer) on which the shell is executing. $PS1 Primary prompt, used by the shell to request a command from the user. $PS2 Secondary prompt, used to request additional info from the user. $PS3 3rd prompt (rarely used). $PS4 4th prompt (rarely used).

= BASH automatically updates the value of certain special variables: Variable ↓ Description ↓ $? Exit status of last pipeline $$ Process ID of the current shell $! Process ID of the last background pipeline $RANDOM Random integer (usually in the range 0-327687).

Retrieving Exist Status = ONLY '0' IS successfull, the rest are error $ ls /tmp >/dev/null $ echo $? 0 $ ls /temp >/dev/null ls: cannot access /temp: No such file or directory $ echo $? 2

$ exit 2 Set exit variable to '2"

$ exit 2143 Set exit variable to '2143"

The test Command

= BASH has a built-in test command (similar to /bin/test) which can perform basic string and integer comparisons using these operators (results are returned as an exit code): = return 0 or 1, where 0 is true, 1 is false

Operator Comparision type Comparison Example -eq Integer Equal $x -eq 4 -ne Integer Not equal $x -ne 4 -gt Integer Greater than $x -gt 0 -lt Integer Less than $x -lt 1000 -ge Integer Greater/equal $x -ge $y = String Equal "$x" = "Y" != String Not equal "$x" != "NEVER"

Unary File Tests Operator Test Example -e File exists [ -e /etc/passwd ] -r File is readable [ -r /etc/hosts ] -w File is writable [ -w /tmp ] -x File is executable [ -x /usr/bin/ls ] -f File is a regular file [ -f /dev/tty ] -d File is a directory [ -d /dev/tty ]

= For example.... $ test 10 -gt 5 $ echo $? 0

$ test 10 -lt 5 $ echo $? 1

$ [ -w /etc/passwd ] $ echo $? 1

$ a=10; [ "$a" -ge 100 -a "$a" -le 1000 ]; echo $? 1

$ [ ! "a" = "b" ]; echo $? 0

$ [ ! "a" != "b" ]; echo $? 1

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BASH FLOW CONTROL

============

Format of 'if'

============

if pipeline then

 success-commands

[elif pipeline2

 else-if-commands

] [else

 alt-commands

] fi

CASE

echo -n "Are you sure you wish to remove '$file'?" read YN if [ "$YN" = "y" -o "$YN" = "Y" ] then

  echo "Deleting '$file'..."
  rm "$file"

else

  echo "Aborted. '$file' not deleted."

fi

if [ "$(date +%Y)" -lt 2010 ] then

  echo "Still waiting for the Whistler Olympics."

fi

Format of "while"

============

while pipeline do

 commands

done

CASE

num=1 while [ $num -le 5 ] do

 echo $num
 num=$[ $num + 1 ]

done

CASE

1. In this case it will just print number 1 to 5

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while (( 1 )) do

 eject -T

done

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Format of "for"

============

for COLOUR in red blue green do

  print "$COLOUR"

done

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for ((x=0; x<=10; x++)) do

  echo $x

done

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for FILE in /etc/* do

  if [ -x $FILE ]
  then
     echo "$FILE is executable"
  fi

done

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RPM

============

RPM file names normally have the following format: <name>-<version>-<release>.<arch>.rpm

== Query / Verify commands

  1. Getting detailed information:
     $ rpm -qi wget
  2. Determining which package installed /usr/bin/wget:
     $ rpm -qf /usr/bin/wget
  3. Showing all the files installed by the package wget:
     $ rpm -ql wget
  4. Viewing the documentation files for the command wget:
     $ rpm -qd wget
  5. Listing all files included in the not yet installed package wget by entering the following:
     $ rpm -qpl /mnt/iso/suse/i586/wget-1.10.2-78.i586.rpm
  6. Listing all files included in the installed package wget:
     $ rpm -ql wget
  7. Verifying that a package is no longer installed by entering:
     $ rpm -qa | grep wget
  8. Seeing what has changed in the files on your hard drive since the wget RPM was originally installed by entering the following:
     $ rpm -V wget
  9. Checking package to ensure its integrity and origin: (NOTE: gpg or pgp software must be installed on your system before you use this command)
     $ rpm -K /mnt/iso/suse/i586/wget-1.10.2-78.i586.rpm

== Install / Uninstall / Upgrade commands

 1. Installing the package wget:
     $ rpm -ivh /mnt/iso/suse/i586/wget-1.10.2-78.i586.rpm
 2. Uninstalling the package wget:
     $ rpm -e wget
 3. Upgrading the package wget: (NOTE: if the package is not installed it will install it for You, like option "-ivh")
     $ rpm -Uvh /mnt/iso/suse/i586/wget-1.10.2-78.i586.rpm
 4. Extracting RPM file using rpm2cpio and cpio command: (NOTE: RPM content will be extracted the current directory)
     $ rpm2cpio wget-1.10.2-78.i586.rpm | cpio -idmv