Using Linux Commands

Using Linux Commands Lab 4

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.

Environment variables :

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

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 • 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 *  remove all files in the current directory

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 metacharactersThis matches any number of characters *

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

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

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 • Use echo command to display text or value of variable. echo [options] [string, variables...]

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 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

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

Using Linux Commands