How does bash differ from sh, the Bourne shell?

How does bash differ from sh, the Bourne shell? 


This is a non-comprehensive list of features that differentiate bash

from the SVR4.2 shell.  The bash manual page explains these more

completely.



Things bash has that sh does not:

	long invocation options

	[+-]O invocation option

	`!' reserved word to invert pipeline return value

	`time' reserved word to time pipelines and shell builtins

	the `function' reserved word

	the `select' compound command and reserved word

	arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done

	new $'...' and $"..." quoting

	the $(...) form of command substitution

	the $(		$(cat filename)

	the ${#param} parameter value length operator

	the ${!param} indirect parameter expansion operator

	the ${!param*} prefix expansion operator

	the ${param:offset[:length]} parameter substring operator

	the ${param/pat[/string]} parameter pattern substitution operator

	expansions to perform substring removal (${p%[%]w}, ${p#[#]w})

	expansion of positional parameters beyond $9 with ${num}

	variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY,

		   TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS,

		   LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME,

		   ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE,

		   HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS,

		   PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC,

		   SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars,

		   auto_resume

	DEBUG trap

	ERR trap

	variable arrays with new compound assignment syntax

	redirections: <>, &>, >|

	prompt string special char translation and variable expansion

	auto-export of variables in initial environment

	command search finds functions before builtins

	bash return builtin will exit a file sourced with `.'

	builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -p/-t.

		  export -n/-f/-p/name=value, pwd -L/-P,

		  read -e/-p/-a/-t/-n/-d/-s,

		  readonly -a/-f/name=value, trap -l, set +o,

		  set -b/-m/-o option/-h/-p/-B/-C/-H/-P,

		  unset -f/-v, ulimit -m/-p/-u,

		  type -a/-p/-t, suspend -f, kill -n,

		  test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S

	bash reads ~/.bashrc for interactive shells, $ENV for non-interactive

	bash restricted shell mode is more extensive

	bash allows functions and variables with the same name

	brace expansion

	tilde expansion

	arithmetic expansion with $((...)) and `let' builtin

	the `[[...]]' extended conditional command

	process substitution

	aliases and alias/unalias builtins

	local variables in functions and `local' builtin

	readline and command-line editing with programmable completion

	command history and history/fc builtins

	csh-like history expansion

	other new bash builtins: bind, command, compgen, complete, builtin,

				 declare/typeset, dirs, enable, fc, help,

				 history, logout, popd, pushd, disown, shopt,

				 printf

	exported functions

	filename generation when using output redirection (command >a*)

	POSIX.2-style globbing character classes

	POSIX.2-style globbing equivalence classes

	POSIX.2-style globbing collating symbols

	egrep-like extended pattern matching operators

	case-insensitive pattern matching and globbing

	variable assignments preceding commands affect only that command,

		even for builtins and functions

	posix mode

	redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr,

		/dev/tcp/host/port, /dev/udp/host/port



Things sh has that bash does not:

	uses variable SHACCT to do shell accounting

	includes `stop' builtin (bash can use alias stop='kill -s STOP')

	`newgrp' builtin

	turns on job control if called as `jsh'

	$TIMEOUT (like bash $TMOUT)

	`^' is a synonym for `|'

	new SVR4.2 sh builtins: mldmode, priv



Implementation differences:

	redirection to/from compound commands causes sh to create a subshell

	bash does not allow unbalanced quotes; sh silently inserts them at EOF

	bash does not mess with signal 11

	sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100

	bash splits only the results of expansions on IFS, using POSIX.2

		field splitting rules; sh splits all words on IFS

	sh does not allow MAILCHECK to be unset (?)

	sh does not allow traps on SIGALRM or SIGCHLD

	bash allows multiple option arguments when invoked (e.g. -x -v);

		sh allows only a single option argument (`sh -x -v' attempts

		to open a file named `-v', and, on SunOS 4.1.4, dumps core.

		On Solaris 2.4 and earlier versions, sh goes into an infinite

		loop.)

	sh exits a script if any builtin fails; bash exits only if one of

		the POSIX.2 `special' builtins fails

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