Brother Bird's Linux private dish notes 6------11 Learn Bash

Source: Internet
Author: User
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1. Legal shell and/etc/shells functions     shell has multiple versions, including Bourne Shell (SH), C shell, K-Shell, tcsh, etc. Normally Linux uses the Bourne Again Shell (Bash), which is the enhanced version of SH       can check/etc/shells to see how many shells are available. Writing a legitimate shell to a/etc/shells file is a way for some of the system's services to check the shells that the user is able to use during the run. When the user logs in, it gets a shell to work, which is recorded in the/etc/passwd file 2.bash Shell function       command memory history, the default command memory function 1000. In the ~/.bash_history file       command completion:tab      alias:alias      Job control, foreground, background (job control, foreground, background)      shell script      wildcard character (Wildcard) 3.bash Built-in command type: View commands from external commands or built-in commands      type [-TPA] name         -T: Display fields are: file, alias, builtin         -P: Displays the full file name when the external command is followed,          -A: In the path defined by path, List all commands that contain name. 4. Variable settings and display unset, echo      variable rules:          variables and variable contents with equals = link   name= "Vbird"           equals can not have space bar           variable name can only be English letters and numbers, the beginning cannot be a number          variable content If there are spaces, use "" or "to expand the variable,               " "in special characters such as $ can be maintained in original features                 ' special characters are only general characters           escape characters \ can be en ter, $, \ etc become general characters.           If there are other commands in a sequence of commands, it can be executed with $ (comand) or comand.           system default variable is usually uppercase, custom variable is lowercase           Cancel variable with unset name5.bash command to open a sub-process s HELL6. Environment variables function      ENV command view the environment variables and common environment variable descriptions           Hoem: Represents the Home folder  CD ~  & nbsp       SHELL: currently used shell          Histsize: Record count           MA IL: Mailbox files read by the system using the Mail command at the time of delivery           PATH: Directory of environment variables           LANG: Language data           random: Random number      set command View all variables (environment variables and custom variables)         &NBSP ; PS1 (prompt setting)           $ (This shell PID): Echo $$         ? (Callback code for previous command)      export: Convert custom variable to environment variable      declare: Can convert environment variable to custom variable 7.locale language variable  /etc/ Default/locale    /ETC/SYSCONFIG/I18N8. Variable keypad reads, arrays and declarations read, array, declare     read [-pt] variable         -P: Follow-up prompt          -T: Number of seconds to wait after the next      DECL is [-AIXR] varibale         -A: Declared array array         -I: declared integer   &NBS P      -x: Declare export environment variable          -r: Set Variable to readonly     var[index]= content     echo "${var[1],${var[2"}} "      recommended ${} Reading array contents 9. Restrictions on file systems and programs: ulimit10. Deletion, substitution, substitution      ${variable# keywords for variable contents}: Array matching keywords from the beginning, deleting the shortest data      ${varibale# #keyword}: Match keywords from the beginning, remove the longest data      ${variable%keyword}    : matches the keyword from the end, Delete the shortest data      ${variable%%keyword}    : from the tailStart matching keywords, remove the longest data      ${variable/old str/new str}: Match the contents of the variable to the old string, replace the first one with the new     ${ Variable//old str/new str}: Replace All
     #: The one with the shortest replacement text      ##: The longest match for the replacement text 11. Test and content substitution for variables                                   &NBSP;STR no setup      str= "        &NBSP;STR set to non-empty      var=${str-expr}         & nbsp;var=expr          var=          var= $str      var=${s TR:-EXPR}          var=expr        var=expr     var= $str   &nbs P &NBSP;VAR=${STR+EXPR}          var=            var=expr   &NBS P   var=expr     var=${str:+expr}          var=         &NB Sp    var=          var=expr     var=${str=expr}    str=expr, var=expr  str unchanged, var= &nbsp  str unchanged, var= $str      var=${str:=expr}   str=expr,var=expr  str=expr,var=expr   Str invariant, var= $str      var=${str?expr}     expr output to stderr    var=       &NBS P  var=str     var=${str:?expr}     expr output to stderr  expr output to stderr  var= Str12. Historical aliases alias unalias          ~/.BASHRC files set 13.bash operating environment       path and command lookup order:           1. Execute commands in absolute relative path           2. The command is found by alias execution       &NB Sp   3. Executed by bash built-in builtin command           4. The first command found in $path order is executed.      bash Login with welcome information/ETC/ISSUE,/ETC/MOTD./etc/update-motd.d in Ubuntu 00-header  10- Help-text file in 14.bash config file       read process with login shell:/etc/profile------------>~/.bash_ Profile--------------> Start bash Operations                         &NBSP ;                ----->/etc/inputrc          -------->~/.b ashrc                                &NBSP ;        ----->/etc/profile.d/*.sh                  &NB Sp                          ,         &NB Sp      --->/etc/sysconfig/i18n      read ~/.bashrc     /when Nologin-bash is obtained Data defined in ETC/BASHRC:          Umask values according to the different UID.           PS1 values based on different UID requirements.           call/etc/profile.d/*.sh settings 15. Terminal Environment Configuration stty,set16. wildcard characters and special symbols       wildcard characters:           *     represents 0 to infinity any character          ?     represents an arbitrary character         &NBSP []     represents a character within brackets           [-]     represents a character within a bracket range           [^]     Non-bracket characters       Special symbols:          #     comments   & nbsp           escape           |     Pipelines          ;     Command delimiter           ~     User home folder           $   &N Bsp Variable           &     Job control, background run          !     non          /          directory symbols         &NBS P >,>>     Data flow redirection, replacement   cumulative           <,<<     Stream redirection           "    no variable substitution function          " "    variable substitution function &nbsp ;     &NBsp   "    commands that can be executed, also available in $ ()           ()     Middle for child shell start and end     &N Bsp     {}     middle command block combination 17. REDIRECT       standard input   code 0, using <,<<      StdOut     Code 1, using >,>>     stderr     code 2, using 2>,2>>    & nbsp, if the error and correct output to the same file, with           find/home-name. BASHRC >list 2>&1           find/home-name. BASHRC &>list       If you discard some of the error messages, use the 2>/dev/ Null18. Pipeline commands       pick command:cut,grep      Sort command:sort,wc,uniq      bidirectional redirection:tee      Character conversion command:tr,col,join,paste,expand      Cut command:split      parameter substitution:xargs      About-: stdout of the previous command as stdin of the current command

Brother Bird's Linux private dish notes 6------11 Learn Bash

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