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Unix Basics

Unix Basics. Unix Basics. Unix directories Important Unix file commands File and Directory Access Rights through Permission Settings Using chmod to change permissions. Unix File Structure. Hierarchical file system Starts at root , denoted “ / ”.

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Unix Basics

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  1. Unix Basics

  2. Unix Basics • Unix directories • Important Unix file commands • File and Directory Access Rights through Permission Settings • Using chmod to change permissions Systems Programming: Unix Basics

  3. Unix File Structure • Hierarchical file system • Starts at root, denoted “/”. • Abstraction is to navigate through the Unix directory structure relative to the current “working” directory. • Slashes separate directory levels. • File names cannot have blanks and lower-case is preferred {case-sensitive}. • Extensions are just conventions to the file system, but NOT to compilers! Systems Programming: Unix Basics

  4. Unix File Notation . = the current directory ..= the parent directory ~= my home directory (i.e., the current directory when I login) File name wild cards ? = any one character * = any zero or more characters Systems Programming: Unix Basics

  5. Unix Commands • Basic format: Command –option parameters e.g. ls –l labs* e.g. cp new.c old.c • C commands can be cryptic and many are only two characters long, but an important exception is: man= manual page request e.g. man ls Systems Programming: Unix Basics

  6. Commands: pwd & ls pwd = print working directory ls = list file names and attributes. -l = long listing -d = list directory itself, not contents -a = all files (including starting with “.”) e.g. ls [just file names] e.g. ls –la [lots of info!] e.g. ls –la labs* [only info labs] e.g. ls –d [just directory names] Systems Programming: Unix Basics

  7. Commands: mkdir & cd mkdir = make a new directory e.g.,mkdir newdir cd = change directory e.g. cd newdir e.g. cd ../updir e.g. cd [change to home directory] Systems Programming: Unix Basics

  8. Commands: mv & cp cp = copy file cp source destination -p= preserve permissions e.g. cp –p new.c old.c e.g. cp prog1.c prog_dir/ mv = move file mv source destination e.g. mv prog1.c distance.c e.g. mv prog1.c prog_dir/ For both commands if the destination is an existing directory, the file name stays the same. Systems Programming: Unix Basics

  9. File and Directory Permissions • Each file or directory has three sets of permissions: • User (i.e. owner) • Note - Only the user can change permissions. • Group • Other (the world!) • Each permission set has three permissions: • Read • Write • Execute These are visible left to right via: ls –la Systems Programming: Unix Basics

  10. File and Directory Permissions • Read access= You can read the file contents. You can list the contents of the directory. • Write access = You can write into this file. You can modify this directory. • Execute access = You can run this file as a command. You can use this directory as part of a path. To access any file, you first need execute permission on all directories from the root to the file. Systems Programming: Unix Basics

  11. Command: chmod chmod = Change mode (permissions) chmod mode files mode: specify users: u, g, or o specify attribute: r, w, or x connect with action: + = add - = delete = = set Systems Programming: Unix Basics

  12. Command: chmod • Examples: chmod u+x prog4.cpp chmod o-r prog4.cpp chmod u=rwx prog4.cpp chmod o+r,g+r prog4.cpp • You can also use octal numbers: chmod 700 prog2.c chmod 750 sample.c Systems Programming: Unix Basics

  13. Commands: emacs, cat, more {generic format} command filename emacs = edit a file e.g. emacs lab1.c cat= printout text file e.g. cat lab1.c more= printout text file (only fill one screen) e.g. more lab1.c • hit the space bar to see more or q to quit. Systems Programming: Unix Basics

  14. Commands: rm, ps, kill rm = delete a file e.g. rm olddat.txt ps = print currently active processes e.g. ps kill = stop one of your running processes e.g. kill -9 26814 Systems Programming: Unix Basics

  15. Example: ps kill $emacs simple.c {inside edit of simple.c} ^z $ps PID TTY TIME CMD 26792 pts/17 00:00:00 tcsh 26814 pts/17 00:00:00 emacs 26815 pts/17 00:00:00 ps $ kill -9 26814 $ [1] Killed emacs simple.c % type this to resume Systems Programming: Unix Basics

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