ICS 54: Brief Notes on Chapter 7: Working with Files and Directories

Handling files and directories

• ls : lists their content and characteristics. There are many options.
  Read the friendly man(ual) in traditional or web form.
• cp [ -i ] : copy one file to another
• mv [ -i ] : move/rename a file
• rm [ -i ] : delete a file
• ln [ -s ] : create [symbolic] link to a file
• mkdir : create a new directory
• rmdir : delete a directory

Protecting Files: Access control

• Each file belongs to an owner and a group
• Each file has protections specified for each of three classes of users:
  • u: the User who owns the file
  • g: members of a Group with access to the file
  • o: Others (anyone other than the owner)
  root (the "super user") has full access
• Three possible permissions:
  • r: read
  • w: write
  • x: execute
• Use ls -l to examine protection of a file
• Use chmod to set protection of a file
  • chmod u-w filename    -- User owning cannot Write
  • chmod g+rx filename    -- Group can Read and eXecute
  • chmod o=r filename    -- Others can Read
  • chmod 751 filename    -- u=rwx, g=rx, o=x
• umask determines (default) permissions of newly created files
  • umask tells the current value
  • umask 027 yields -rw-r-----, drwxr-x---
  • umask 026 yields -rw-r-----, drwxr-s--x

File Permissions

% ls -liga
total 28
611243 drwxr-x---  5 unixguru fish       512 Apr 1 12:41 .
 80715 drwxr-r-x   4 unixguru fish       512 Apr 1 12:27 ..
611302 -r--------  1 unixguru fish      1674 Apr 1 12:31 400
611297 -rw-------  1 unixguru frogs     2034 Apr 1 12:31 600
611290 -rw-r-----  1 unixguru fish       970 Apr 1 12:28 640
611273 -rw-r--r--  2 unixguru fish      2604 Apr 1 12:28 644
611273 -rw-r--r--  2 unixguru fish      2604 Apr 1 12:28 644L
611292 -rwxr-x--x  1 unixguru swimmers  6267 Apr 1 12:29 751
625316 drwx------  3 unixguru swimmers   512 Apr 1 12:37 d700
634698 drwxr-x---  2 unixguru frogs      512 Apr 1 12:39 d750
620629 drwxr-x--x  4 unixguru frogs      512 Apr 1 12:35 d751

Exploring Files

• ls [ -aAbcCdfFgilLmnopqrRstux1 ] filename
• file filename    -- what kind of file is this?
• find where2look -name filename -print
• wc filename    -- Word Count
• cat filename    -- the friendly man says,
  "cat - concatenate files and print on the standard output"
      cat filename | wc
• Look at longer files with pg, more, and less.