Bash Reference Manual

from version 3.2.57 ^ there exists version 5.1 as of 12/2020

Introduction
• What is a shell? What's Bash? A user interface, command language interpreter, a macro processor which takes text and symbols, expanding them to create larger expressions and executes commands.
  Files containing commands can be treated as commands. Ones with the same name as commands are executed instead of the system command.

  Basic Features Operation Quoting Double "      $ ,  ` , and  \ are special Single ' Escape Character \ ANSI-C \n newline Locale-Specific Translation Comments # Commands simple pipelines | lists && ||     & ; compound (list) group { list; } Conditional if [ $? -eq 0 ];then echo good; else echo BAD; fi $NUM -eq 14 , -ne, -lt, -le, -gt $STRING=='ok', !=, < , > -d name directory,  -e exists, -r -w -x loops for i in 3 2 1 ; do echo $i ; done for (( i=1; i<3; i++ )) do echo $i; done i=0; until [ $i -gt 3 ]; do echo $i ; ((i++)) ; done while [ `itsready` ]; do echo 1;done Defining Functions function name() { … return rc; } Parameters Positional DaFunc $min, $nterval             $0       $1, $2 … Special $*, $@, $#, $?, $-, $$, $_, $0	Expansions Brace { } Tilde ~ Parameter $ echo ${LINES:=30} Command Substitution export LOG=`date +log/%y%m%d.%H%M` Arithmetic     echo $(($COLUMNS-40)) Process Substitution       <(list)   or       >(list) Word Splitting Filename Pattern Matching Quote Removal Redirecting I/O STDIN cmd < f STDOUT cmd > f Appending Output >> STDERR with STDOUT  >f 2>&1  Here Documents << stop Duplicating File Descriptors Opening File Descriptors for Reading and Writing Executing Commands Simple Command Expansion Command Search and Execution Command Execution Environment Environment name=value Exit Status if [ $RC -ne 0 ];then echo … Signals Scripts Features Other Bourne Features Major Differences SVR4.2 Bourne Implementation Differences SVR4.2	Invoking and arguments    (alternate or no initial files, etc.) Startup Files /etc/profile ~/.bash_profile ~/.bash_login ~/.profile Builtin Commands    echo, if, cd, while etc bash Variables Arrays Directory Stack Controlling the Prompt The Restricted shell POSIX Mode Job Control Basics Builtins Variables Command History Facilities Expansion Event Designators Word Designators Modifiers
  Command Line Editing

  Parameter and Variable

  Functions

  Concepts

  ---

  Builtin Commands

  .    :   [    alias    bg    bind    break    builtin    cd    command    continue    declare    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      

  SPECIAL builtin commands

  Cannot be invoked with nice.
  . : break continue eval exec exit export readonly return set shift times trap unset history suspend   

  Reserved Words

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

  Installing Bash

  Basic Installation	Compilers and Options	Compiling For Multiple Architectures	Installation Names
  Specifying the System Type	Sharing Defaults	Operation Controls	Optional Features

  DGG made this nice stuff from, what is now, and old version of the docs.
  

  The truth is out there gnu.org/software/bash/manual/bashref.html

  > bash --help # as of 7/28/16 GNU bash, version 4.1.2(1)-release-(x86_64-redhat-linux-gnu) Usage: bash [GNU long option] [option] ... bash [GNU long option] [option] script-file ... GNU long options: --debug --debugger --dump-po-strings --dump-strings --help --init-file --login --noediting --noprofile --norc --rcfile --posix --restricted --protected --rpm-requires --verbose --version Shell options: -irsD or -c command or -O shopt_option (invocation only) -abefhkmnptuvxBCHP or -o option Type `bash -c "help set"' for more information about shell options. Type `bash -c help' for more information about shell builtin commands. (The following are rearranged, i.e. not exactly as displayed.) > sh -c "help set" set: set [--abefhkmnptuvxBCHP] [-o option] [arg ...] -o option-name Set the variable corresponding to option-name: variable flag allexport -a Mark variables which are modified or created for export. braceexpand -B the shell will perform brace expansion errexit -e Exit immediately if a command exits with a non-zero status. errtrace -E ERR trap is inherited by shell functions. functrace -T If set, the DEBUG trap is inherited by shell functions. hashall -h Remember the location of commands (i.e. save them in a cache like structure) history enable command history histexpand -H Enable !nth style history substitution. Default on when shell is interactive. Retrieve the -nth command or first argument(!^) or last argument(!$) or all arguments (!*). Format !n:w. geek.nz has more info. ignoreeof the shell will not exit upon reading EOF keyword -k All assignment arguments are placed in the environment for a command, not just those that precede the command name. noclobber -C disallow existing regular files to be overwritten by redirection of output. noglob -f Disable file name generation (globbing). monitor -m Job control is enabled. notify -b Notify of job termination immediately. nounset -u Treat unset variables as an error when substituting. onecmd -t Exit after reading and executing one command. physical -P do not follow symbolic links when executing commands such as cd which change the current directory. pipefail the return value of a pipeline is the status of the last command to exit with a non-zero status, or zero if no command exited with a non-zero status privilege -p Turned on whenever the real and effective user ids do not match. Disables processing of the $ENV file and importing of shell functions. Turning this option off causes the effective uid and gid to be set to the real uid and gid. vi use a vi-style line editing emacs use an emacs-style line editing noexec -n Read commands but do not execute them. verbose -v display shell input lines as they are read. xtrace -x display commands and arguments as they are executed. posix operate as 1003.2 standard interactive- comments allow comments to appear in interactive commands

  - Assign any remaining arguments to the positional parameters.
  The -x and -v are turned off.
  Using + causes flags to be turned off.
  The flags can be used at invocation of the shell, current set of flags may be found in $-. echo $- himBH (hashall, jobcontrol, Braceexpand, HistExpand )
  The remaining n ARGs are positional parameters and are assigned, in order, to
  $1, $2, … $n.
  If no ARGs are given, all variables are output.
  

  set BASH_COMPLETION_COMPAT_DIR=/etc/bash_completion.d empty  ??
  
  /etc/bashrc_Apple_Terminal :
      
  
  
  
  Versions
  Mac  OS  has an older version of bash 3.2.57.(1). It will not include newer versions, 
  
  as well as several other commands (including: sed )
  
  becuse they have a GPL V3 license that explicitly restricts commercial Unix vendors from including them.  
  
  Where there is an open source command you are allowed to install it (in an unprotected directory, safe from Mac OS upgrades).
  Package managers that can add them include:  Homebrew, MacPorts, Fink.
  
  Various distrbutions:
  
  cygwin 2.05b.0(8)-release
  
  @Real-World-Systems.com : BASH_VERSION=GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)   
  
  > ls -l /bin/sh
  
  lrwxrwxrwx 1 root root 4 Nov 20  2014 /bin/sh -> bash
  
  
  
  Changes of note:
  
  ⌘ : 
   > /bin/sh -c 'echo -e "Hello\n\tWorld"'
  -e Hello
      World
   
  > /bin/bash -c 'echo -e "Hello\n\tWorld"'
  Hello
      World 
  
  Severly hacked by Dennis G German beginning 12/18/01 and continuing today
  
  
  Sub versions up to -53 exist( these do not change functionally but correct bugs
  
  -53