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Using Linux Commands. Lab 4. Using the Shell in Linux Commands Syntax. Options: could be added to the commands to change their behavior (-a , -la , --help) Argument: is an extra piece of information (ex.: a file name) Environment variables :

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Using the shell in linux commands syntax
Using the Shell in LinuxCommands Syntax

  • Options:

    could be added to the commands to change their behavior(-a , -la , --help)

  • Argument:

    is an extra piece of information(ex.: a file name)

  • Environment variables :

    where the shell stores information that may be useful to the user’s shell session.

    Examples of environment variables include $SHELL (which identifies the shell you are using )and$PS1 (which defines your shell prompt)

    Meta characters:

    that have special meaning to the shell

    • (>) used to direct the output of a command to a file.

    • ( | ) pipe the output to another command.



Getting help with using the shell
Getting Help with Using the Shell

  • Use --help with the command(date --help)


  • Use theman command

    • man = manual

    • To reading a manual and return to the shell prompt within the open terminal  press q


Understanding file permission
Understanding file permission

  • Why

  • Keep users from accessing other users’ private files

  • To protect important system files

  • permissions bits

    rwx rwx rwx

    Owner’s| Group | Others

    r = read w = write x = execute


Understanding file permission1
Understanding file permission

For Files:

  • "Read" means to be able to open and view the file

  • "Write" means to overwrite or modify the file

  • "eXecute" means to run the file as a binary files are executable only if they are programs and shell scripts, not useful for data files.

    For Directories:

  • "Read" means to be able to view the contents of the directory

  • "Write" means to be able to create new files/directories or delete files/directories within the directory

  • "eXecute" means to be able to "Change Directory" (cd) into the directory = permission to access the directory.

  • How to view the permission for a file or directory?

    • $ ls -al


  • Understanding file permission2
    Understanding file permission

    d ≡ directory

    -≡ file

    Permission for the group

    Permission for the others

    Permission for the owner

    • if the permission field is -  the permission is not given.


    Understanding file permission3
    Understanding file permission

    • Only the owner of a file can change its permission.

    • How to set file permission?

      • Use the command chmod(change file mode bits).

    • chmod has two notations:

      • Numeric(octal) notation.

      • Symbolic notation.


    Change permission on a file numeric
    Change permission on a file - numeric

    • the file permissions aren't represented by characters. Instead, they are represented by a three-digit octal number.

    • 4 = read (r)2 = write (w)1 = execute (x)0 = no permission (-)

    If the permission is

    725

    4+2+1

    0+2+0

    4+0+1

    r-x

    rwx

    -w-


    Change permission on a file symbolic
    Change permission on a file – symbolic

    • Permissions are represented by characters rwx

    • This gives “who” the specified permissions for a given filename.

    • The “who” is a list of letters re going to be giving permissions to. These may be specified in any order.

    • +  add the selected permission.

    • -  remove the selected permission.


    Change permission on a file
    Change permission on a file

    For r, w, x octal value is 4,2,1 respectively

    owner(u) group(g) other(o) all(a)rwxrwxrwx

    owner(u) group(g) other(o) all(a)---------



    Creating files and directories
    Creating files and directories

    • Use the command mkdir to create a new directory to the current working directory.

    • $ mkdirdirectoryName


    Creating directories exercise
    Creating directories (Exercise)

    • Go to your home directory. Type cd.

    • Make sure that you got to your home directory, type pwd

    • Create a new directory called test in your home directory:

    • Check the permissions of the directory by typing: ((The -d option tells ls not to list the contents of the test directory; just show us the listing for the directory itself)).

    • Suppose that you want to prevent everyone else from using or viewing the files in this directory:

    • Make the test directory your current directory :



    Creating directories
    Creating directories

    • To create a directory(test) in the Desktop, we have two ways:

      • mkdir /home/chris/Desktop/test

      • cd /home/chris/Desktopmkdir test

    • NOTE:

      • The -d option tells ls not to list the contents of the test directory; just show us the listing for the directory itself.





    Moving copying and deleting files1
    Moving, copying, and deleting files

    *  remove all files in the current directory



    After remove application file
    After remove application file.


    Winows file before and after (cp command )


    Create empty files
    Create empty files

    • To create an empty file in the current directory use the command touch

    • $ touch file1 file2 file3

    Using file-matching metacharacters

    • Metacharacters help to match one or more files without typing each filename completely.

      • * This matches any number of characters(zero or more characters).

      • ? This matches any one(single) character.

      • […] This matches any one of the characters between the brackets, which can include a dash-separated rang of letters or numbers.


    Using file matching metacharacters this matches any number of characters
    Using file-matching metacharactersThis matches any number of characters *


    Using file matching metacharacters this matches any one single character
    Using file-matching metacharactersThis matches any one(single) character?


    Using file matching metacharacters this matches any one of the characters between the brackets
    Using file-matching metacharactersThis matches any one of the characters between the brackets […]


    Using file redirection metacharacters
    Using file-redirection metacharacters

    • < Direct the contents of a file to the command

    • > Direct the output of a command to a file, overwriting any existing file

    • >> Direct the output of a command to a file, adding the output to the end of

    • existing file


    Echo command
    echo Command

    • Use echo command to display text or value of variable.

      echo [options] [string, variables...]


    Quotes
    Quotes

    • "Double Quotes“

      • variables and command substitution(except \and $).

    • 'Single quotes‘

      • protects everything enclosed between two single quote marks.

      • It is used to turn off the special meaning of all characters ( NOsubstitution of variables and commands).

    • `Back quote`

      • Used with commands only.

      • To execute command.


    Echo command1
    echo Command

    • Options-nDo not output the trailing new line.-eEnable interpretation of the following backslash escaped characters in the strings:

      \a alert (bell)\b backspace\n new line\t horizontal tab



    References
    References

    http://www.podgrid.org/linux-bible/linux-bible-page109.html


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