Lecture Three

Pathnames; Filename Expansion; Shell Basics

Pathnames

• absolute pathnames start with /, representing the root, and continue with the directory structure to the destination filename or directory name
• relative pathnames do not start with /, and are relative to your current (or working) directory
• relative-to-home pathnames are actually absolute, but use ~ to represent the home directory
  • ~ replaced by $HOME, eg. ~/pathname
  • ~user replaced by home directory of user, eg. ~user/pathname

Filename Expansion

• also called ambiguous file references, metacharacters, wild card characters, and filename generation characters
• used to find filenames that match a pattern
• ? matches any single character, eg. echo temp?2
• * matches any number (including none) of characters, eg. ls temp*
• a leading period (hidden file) must be explicitly specified, eg. echo * - will not show hidden files
• [ ] matches any single character in included list, eg. ls temp[12]*
• - within [ ] between two characters represents a range, eg. ls temp[1-58] is the same as ls temp[123458]
• if ! is first character within [ ], then any character not in list is matched

Shell Basics

• command history
  • or - move to previous command or next command
  • fc -l - display last 16 commands
  • history - display all commands in buffer
  • !num - re-execute command number "num"
  • !xxx - re-execute last command beginning with string "xxx"
• some useful BASH keyboard shortcuts:
  • erase Characters: Backspace or Ctrl-Backspace or Ctrl-h
  • go to the beginning of the line: Ctrl-a
  • go to the end of the line: Ctrl-e
  • delete a word before the cursor: Ctrl-w
  • delete everything before the cursor: Ctrl-u
  • clear screen: Ctrl-l
  • search for a keyword in previous commands: Ctrl+r
  • auto-complete file/directory names: Tab

Quoting

• one reason for quotes is so that string values can contain spaces and special chars
• three styles of quoting:
  • single quotes ' ' (strong quotes - don't allow variable and command substitution)
  • double quotes " " (weak quotes - allow variable and command substitution)
  • backslash \ (quotes the next character only)

• quoting examples:

   ==> school=Seneca                     # Assign a variable
  
   ==> mySchool=my school is $school     # This will cause an error
  bash: school: command not found
  
   ==> mySchool="My school is $school"   # Weak quotes, allowing substitution
  
   ==> echo $mySchool
  My school is Seneca
  
   ==> mySchool='My school is $school'   # Strong quotes, not allowing substitution
  
   ==> echo $mySchool
  My school is $school
  
   ==> mySchool=My\ school\ is\ $school  # Equivalent of weak quotes
  
   ==> echo $mySchool
  My school is Seneca
  
   ==> mySchool=My\ school\ is\ \$school # Equivalent of strong quotes
  
   ==> echo $mySchool
  My school is $school
  
   ==> dirListing=$(ls -l)               # Command substitution
  
   ==> echo $dirListing                  # Spacing is not preserved
  total 0 -rw------- 1 lczegel users 0 Oct 10 17:54 file1 -rw------- 1 lczegel use
  rs 0 Oct 10 17:54 file2 -rw------- 1 lczegel users 0 Oct 10 17:54 file3
  
   ==> echo "$dirListing"                # Spacing is preserved
  total 0
  -rw------- 1 lczegel users 0 Oct 10 17:54 file1
  -rw------- 1 lczegel users 0 Oct 10 17:54 file2
  -rw------- 1 lczegel users 0 Oct 10 17:54 file3
   ==> _