• Bash Note

Bash Note

• Syntax:
  • Lexical elements:
    • identifier: start with [_a-zA-Z], and makeup with [_a-zA-Z0-9].
    • keyword:
      • builtin:

          ., :, [, ], alias, bg, bind, break, builtin, caller, cd,
          command, compgen, complete, compopt, continue, coproc,
          decalare, dirs, disown, echo, enable, eval, exec, exit, export,
          fc, fg, getopts, hash, help, history, jobs, kill, let, local,
          logout, mapfile, popd, printf, pushd, pwd, read, readarray,
          readonly, return, set, shift, shopt, source, suspend, test,
          times, trap, type, typeset, ulimit, umask, unalias, unset,
          wait.
        

      • shell:

          !, [[, ]], {, }, case, do, done, elif, else, esac, fi, for,
          function, if, in, select, then, time, until, while
        

    • constant: text.
    • operator: ```
      • escape special or continue line: .
      • quote a string: ‘str’, “str”.
      • source file: . file.

      • pipe:

        ,

        &

      • lists of command: ;, &, &&,

      • group command: ( list ), { list; }
      • test: [ expr ], [[ expr ]], ((expr)). -(a|b|c|d|e|f|g|h|k|p|r|s|t|u|w|x|G|L|N|O|S) file, file1 -(ef|nt|ot) file2, -o optname -(v|R) var -(z|n) str str1 (==|=|!=|<|>) str2 arg1 -(eq|ne|lt|le|gt|ge) arg2
      • assignment: name=value, array=(a b c d).
      • data access: $name, ${name}.
      • Special parameters: $*, $@, $#, $?, $-, $$, $!, $0, $_, $n.
      • Expansions:
        • brace: {a,b,c}, {a..b..c}.
        • tilde: ~, ~+, ~-, ~N, ~+N, ~-N.
        • parameters: ${para:(-|=|?|+)word}, ${para:off:len}, ${!prefix}, ${prefix@}, ${!name[]}, ${!name[@]}, ${#para}, ${para#word}, ${para##word}, ${para%word}, ${para%%word}, ${para/pat/str}, ${para^pat}, ${para^^pat}, ${para,pat}, ${para,,pat}, ${para@(Q|E|P|A|a)}.
      • cmd sub: $(cmd), cmd.
      • arithmetic: $((expr)) id++, id–, ++id, –id, -id, +id, !expr, ~, **, *, /, %, +, -, «,

        , <=, >=, <, >, ==, !=, &, ^,	, &&,		, ?:, =, *=, /=, %=, +=,
        -=, «=, »=, &=, ^=,	=, expr1, expr2

      • process substitution: <(list), >(list).

      • filename expansion: *, ?, […], (?

        *

        +

        @

        !)(pat).

      • redirection: [N]<word, [N]>|word, [N]»word, &>word, >&word, &»word, [N]«[-]word, [N]«<word, [N]<&word, [N]>&word, [N]<&DIG-, [N]>&DIG-, [N]<>word.
      • history: !, !N, !-N, !!, !string, !?string[?], ^str2^str2^, !#, !(str|!|N|-N):(0|N|^|$|%|X-Y||X|X-):(h|t|r|e|p|q|x|s/old/new/G?|&|gs/old/new/|as/old/new/) ```
    • delimeter: white space characters, and comment characters, #.
  • Syntax elements:
    • type:

        'string', "string", string
        (str1 str2 str3 ...)
      

    • expression:

        see operator->test or operator->arithmetic.
      

    • statement: ```

      • pipelines: [time [-p]] [ ! ] command [ [

        ⎪

        &] command2 … ].

      • lists: command1 && command2, command1

        command2.

      • Compound Commands:
        • (list), { list; }, ((expression)), [[ expression ]]
        • condition:
          • if list; then list; [ elif list; then list; ] … [ else list; ] fi

          • case word in [ [(] pattern [

            pattern ] … ) list ;; ] … esac

          • select name [ in word ] ; do list ; done
        • loops:
          • for name [ [ in [ word … ] ] ; ] do list ; done
          • for (( expr1 ; expr2 ; expr3 )) ; do list ; done
          • while list-1; do list-2; done
          • until list-1; do list-2; done
      • Coprocesses: coproc [NAME] command [redirections]
      • Shell Function Definitions:
        • name () compound-command [redirection]
        • function name [()] compound-command [redirection] ```
    • decalaration:

        array=(str1 str2 str3 ...)
        [function] func[()] { compound-cmd } [ redirections ]
        decalare -i intger_var
        decalare -(a|A) array_var
        decalare -f func_name
      

    • scope:

        local: local, normal assignment, function define
        global: export, decalare -x
      

    • data access: ```
      • see parameters expansion: Special parameters, Expansions->parameters.
      • normal: $var, ${var}, ${var[n]}.
      • function: func_name arg1 arg2 … ```
  • Others:
    • preprocess: no, use source to include source files.
    • template: no.
    • namespace: no.
• Feature:
  • Paradigm: dynamic scripting , procedural, text oriented and cmd oriented language.
  • (Package|Library) managment: use builtin source cmd to include source file which act as library.
  • OOP: no
  • FP: no
  • GC: no
  • VM: no
  • Thread: no
  • Misc:
    • use external cmd to expand the feature.
    • use text output more then return value.
    • text oriented and cmd oriented language.
    • use builtin cmds and execute environment, and predefine variables.
    • 0 and ‘‘(empty string) are true, others are false.
    • builtin jobs control, cmd completion, pipe, coprocess, alias, history review, powerful expansion.
• Library:
  • Standard library: no, but has builtin cmds.
  • Third-party library: external cmd as library.