Using linux commands
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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 Linux Commands

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Using linux commands

Using Linux Commands

Lab 4


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.


Using linux commands

Environment variables :


Getting help with using the shell

Getting Help with Using the Shell

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


Using linux commands

  • 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 = readw = writex = 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)---------


    Using linux commands

    Set different permissions of start file:


    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 :


    Using linux commands

    Answer


    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 files

    Moving, copying, and deleting files


    Rename file start start1

    Rename file start start1


    After rename the file

    After rename the file


    Moving copying and deleting files1

    Moving, copying, and deleting files

    *  remove all files in the current directory


    Before remove application file

    Before remove application file.


    After remove application file

    After remove application file.


    Using linux commands

    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


    Examples of quoting special characters

    Examples of quoting special characters


    References

    References

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


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