ksh script entry

the basics of ksh (Korn shell)

• alias
  used as convenient names for commands. for example, if ll command not found, you can type alias ll='ls -l' in environment file of current user.

• options
  one way of changing the behavior of shell, the basic command of related to it are set -o optionnames and set +o optionnames. some options like
  (1)allexport
  (2)ignoreeof #if on, do not allow Ctrl+D to exit
  (3)noglob
  note: most have one-letter counterpart as its abbr.

• scripts
  A script/file is a shell program that contains some shell commands. In files of the kind, the #!/usr/bin/ksk line is generally used as Shebang one. Three methods of running scripts:
   (1)[user@host ~]$ ./script_name [&] or script_name [&] #run included commands in the subshell/subprocess but no need to wait until subshell is done
     (2)[user@host ~]$ [.|source] script_name #run in current/same shell
    (3)[user@host ~]$ [ksh|bash|sh] script_name #same as (1)

• functions
  a sort of a script-within-a-script by which to define some shell code by name and store it in shell’s memory , to invoke and run it later as if it were a shell script. two forms of function definition:

function func_name {
    ...
    shell code/chunk
    ...
} #as one
func_name () {
    ...
    shell code/chunk
    ...
} #as the other

• autoload functions
  put autoload func_name in profile or environment file of specific login user
  . Doing like this make it that shell will not read in definitions of function until it is actually called. for example, in your profile file:
  FPATH=~/kshfuncs
autoload testf

  When you invoke the command testf , the shell will look in the directory ~/kshfuncs for a file called testf that has the definition of function testf . If it doesn’t find the file, or if the file exists but doesn’t contain the proper function definition, the shell will complain with a “not found” message, just as if the command didn’t exist at all

• string operator
  curly-bracket(花括號) syntax allows for string operators which manipulates values of variables in various useful ways. generally you can do:
    (1)test for variable existence
    (2)set default value of variables
    (3)catch errors that result from variables not being set
  use syntax: ${var_name:[-|=|+|?][word|msg]}

• regular expression and pattern-matching operator
  syntax format looks like:

[*|+|?|!](exp)  #
@(exp1|exp2|...) #or 
${var_name#pattern} #
${var_name##pattern} #
${var_name%pattern} #
${var_name%%pattern} #

extra points

• typeset -f[u]
  print functions defined in current login session while -u opt outputs autoload ones

• whence
  alias to type -a , it prints extra source(準確來源) or pathname of a command/function whose name as argument. an example looks like
  [user@host ~]$ whence cd
[user@host ~]$ cd is a shell buitin
[user@host ~]$ whence man
[user@host ~]$ man is /usr/bin/man