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.(See Invocation. ) version Show the version number of this instance of bash when starting. quiet Do not be verbose when starting up (do not show the shell version or any other information).This is the default. login Make bash act as if it had been invoked as a login shell. nobraceexpansion Do not perform curly brace expansion.(See Brace Expansion, later in this manual page.) nolineediting Do not use the GNU readline library to read command lines if interactive. posix Change the behavior of bash where the default operation differs from the POSIX 1003.2standard to match the standard.ARGUMENTSIf arguments remain after option processing, and neither the c nor the s option has been supplied, the first argument isassumed to be the name of a file containing shell commands.If bash is invoked in this fashion, is set to the name of the file,and the positional parameters are set to the remaining arguments.bash reads and executes commands from this file, thenexits.bash s exit status is the exit status of the last command executed in the script. Part I: User Commands12DEFINITIONSblank A space or tab.word A sequence of characters considered as a single unit by the shell.Also known as a token.name A word consisting only of alphanumeric characters and underscores and beginning with analphabetic character or an underscore.Also referred to as an identifier.meta character A character that, when unquoted, separates words.One of the following:|, &, ;, (, ), , space, tabcontrol operator A token that performs a control function.It is one of the following symbols:||, &, &&, ;, ;;, (, ), |,RESERVED WORDSReserved words are words that have a special meaning to the shell.The following words are recognized as reserved whenunquoted and either the first word of a simple command (see Shell Grammar, next) or the third word of a case or forcommand:! case do done elif else esac fi for function if in select then until while { }SHELL GRAMMARSIMPLE COMMANDSA simple command is a sequence of optional variable assignments followed by words and redirections separated by blank andterminated by a control operator.The first word specifies the command to be executed.The remaining words are passed asarguments to the invoked command.The return value of a simple command is its exit status, or 128+n if the command is terminated by signal n.PIPELINESA pipeline is a sequence of one or more commands separated by the character |.The format for a pipeline is[!]command [ | command2.]The standard output of command is connected to the standard input of command2.This connection is performed before anyredirections specified by the command.(See the Redirection section, later in this manual page.)If the reserved word ! precedes a pipeline, the exit status of that pipeline is the logical NOT of the exit status of the lastcommand.Otherwise, the status of the pipeline is the exit status of the last command.The shell waits for all commands inthe pipeline to terminate before returning a value.Each command in a pipeline is executed as a separate process (that is, in a subshell).LISTSA list is a sequence of one or more pipelines separated by one of these operators: ;, &, &&, or ||, and terminated by one ofthese: ;, &, or.Of these list operators, && and || have equal precedence, followed by ; and &, which have equal precedence.If a command is terminated by the control operator &, the shell executes the command in the background in a subshell.Theshell does not wait for the command to finish, and the return status is 0.Commands separated by a ; are executed sequen-tially; the shell waits for each command to terminate in turn.The return status is the exit status of the last commandexecuted.The control operators && and || denote AND lists and OR lists, respectively.An AND list has the form:command && command2command2 is executed if, and only if, command returns an exit status of Zero. bash13An OR list has the formcommand command2command2 is executed if, and only if, command returns a non zero exit status.The return status of AND and OR lists is the exitstatus of the last command executed in the list.COMPOUND COMMANDSA compound command is one of the following:(list)list is executed in a subshell.Variable assignments and built-in commands that affect the shell s environment do not remainin effect after the command completes.The return status is the exit status of list.{ list; }list is simply executed in the current shell environment.This is known as a group command.The return status is the exitstatus of list.for name [ in word;] do list ; doneThe list of words following in is expanded, generating a list of items.The variable name is set to each element of this list inturn, and list is executed each time.If the in word is omitted, the for command executes list once for each positionalparameter that is set.(See Parameters, later in this manual page.)select name [ in word;] do list ; doneThe list of words following in is expanded, generating a list of items
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