UNIX

UNIX

1. Pathname

   • Root
     • Always starts with forward slash
   • Relatives
     • Relative parthname are quickly to use than absolute pathnames, because their point of departure is the current working directory rather than the root
   • Absolutes
     • An absolute pathname identifies a file by starting at the root , irrespective of which directory the user is in at the time

2. Commands to work with directories

   • Command ls to list the contents of a directory to screen
     • -a displays all the files in the current directory including hidden files, which are prefixed with a dot
     • -f identifies the types of files in a listing
     • -G colorizes screen output so that categories of files can be seen easly
     • -l displays details about each file in a directory, such as its type, permissions, owner, size stc
     • -r reverses the order in which the files in a directory would be displayed by default
     • -t displays files according to their modification times

3. cat command allows you to view and modify the contents of a file. it also allows you to combine two existing files to create a new one

   • -b numbers all the lines in a file except blank lines
   • -n numbers all the lines in a file
   • -u allows you to prevent the command from buffering screen output. this is useful when the file is large and the system memory is limited

4. Creating a File

   • touch command to create a new file with the name you specify, default permissions and can modify existing files
   • Redirections before command such as echo, cat or ls is executed, you can redirect its output to a file using the > notation
   • Application Files are often created when you use an application such as vi, or macs text editor. To edit, save an give it a name

5. rm command to delete files, either simgle or in multiple

   • -r to delete the contents recursively
   • -P Overwrite regular files before deleting them
   • -d like the r option, attempt to remove directories as well as files
   • -v Be verbose when deleting files, displaying each as it is remove
   • -i Request confirmation before removing the specified file
   • -f Attempt to remove files without prompting for confirmation, irrespective of file permission

6. Permissions

   • read = 4, read files or list the contents of a directory
   • white = 2 to modify a file or create an delete in a directory
   • execute = 1 to run a file, if it's a program or script, or access files in the directory
   • Every file and directory also has three groups "owner" "group" "other user"

7. wilecards and regular expresion

   • the * wildcard matches zero or more instances of any character
   • the ? wildcard matches a single instance of any character
   • the [ ] wildcard to match sets of chararcters. You can include lists of characters or specify a range
   • the ! wildcard within [ ] matches any chararctes that is not listed in the square brakets

8. the find command seach a file when you do not know where it is located

   • -atime to find files according to their access time (find /-atime 2)
   • -ctime to find files according to their modification time (fine /-ctime 2)
   • -group to fine files according to their owner (fine /-group <name_group>)
   • -size to fine files according to their size (fine /-size 10)
   • -name fine /home -name <namefile>

9. grep to search the content within local files using the siyntax grep <options><regular exprexion> <file>

   • -c option suppresses output by printing a count of maching lines for each input file
   • -h to suppress prefixing of filesnames on output when searching multiple files
   • -H prints the filename for each match
   • -i allows you to ignore case distinction in both the pattern and input files
   • -n when you want to prefix each line of output with line number within its input file
   • -v to print nonmatches lines for each input file
   • -w to search for a specific pattern as word