bash shell

BASH(1) USER COMMANDS BASH(1) NAME bash - GNU Bourne-Again SHell SYNOPSIS bash [options] [file] COPYRIGHT Bash is Copyright (C) 1989, 1991 by the Free Software Foun- dation, Inc. DESCRIPTION Bash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. Bash also incorporates useful features from the _K_o_r_n and _C shells (ksh and csh). Bash is ultimately intended to be a conformant implementa- tion of the IEEE Posix Shell and Tools specification (IEEE Working Group 1003.2). OPTIONS In addition to the single-character shell options documented in the description of the set builtin command, bash inter- prets the following flags when it is invoked: -c _s_t_r_i_n_g If the -c flag is present, then commands are read from _s_t_r_i_n_g. If there are arguments after the _s_t_r_i_n_g, they are assigned to the positional param- eters, starting with $0. -i If the -i flag is present, the shell is _i_n_t_e_r_a_c_- _t_i_v_e. -s If the -s flag is present, or if no arguments remain after option processing, then commands are read from the standard input. This option allows the positional parameters to be set when invoking an interactive shell. - A single - signals the end of options and disables further option processing. Any arguments after the - are treated as filenames and arguments. An argument of -- is equivalent to an argument of -. Bash also interprets a number of multi-character options. These options must appear on the command line before the single-character options to be recognized. -norc Do not read and execute the personal initializa- tion file ~/._b_a_s_h_r_c if the shell is interactive. This option is on by default if the shell is invoked as sh. -noprofile Do not read either the system-wide startup file /_e_t_c/_p_r_o_f_i_l_e or any of the personal initialization GNU Last change: 1995 May 5 1 BASH(1) USER COMMANDS BASH(1) files ~/._b_a_s_h__p_r_o_f_i_l_e, ~/._b_a_s_h__l_o_g_i_n, or ~/._p_r_o_- _f_i_l_e. By default, bash normally reads these files when it is invoked as a login shell (see INVOCA- TION below). -rcfile _f_i_l_e Execute commands from _f_i_l_e instead of the standard personal initialization file ~/._b_a_s_h_r_c, if the shell is interactive (see INVOCATION below). -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 below). -nolineediting Do not use the GNU _r_e_a_d_l_i_n_e library to read com- mand lines if interactive. -posix Change the behavior of bash where the default operation differs from the Posix 1003.2 standard to match the standard ARGUMENTS If arguments remain after option processing, and neither the -c nor the -s option has been supplied, the first argument is assumed to be the name of a file containing shell com- mands. If bash is invoked in this fashion, $0 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, then exits. Bash's exit status is the exit status of the last command executed in the script. DEFINITIONS blank A space or tab. word A sequence of characters considered as a single unit by the shell. Also known as a token. name A _w_o_r_d consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underscore. Also referred to as an identifier. metacharacter A character that, when unquoted, separates words. One of the following: | & ; ( ) < > space tab control operator A _t_o_k_e_n that performs a control function. It is one of the following symbols: || & && ; ;; ( ) | <newline> GNU Last change: 1995 May 5 2 BASH(1) USER COMMANDS BASH(1) RESERVED WORDS _R_e_s_e_r_v_e_d _w_o_r_d_s are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted and either the first word of a simple command (see SHELL GRAMMAR below) or the third word of a case or for com- mand: ! case do done elif else esac fi for function if in select then until while { } SHELL GRAMMAR Simple Commands A _s_i_m_p_l_e _c_o_m_m_a_n_d is a sequence of optional variable assign- ments followed by _b_l_a_n_k-separated words and redirections, and terminated by a _c_o_n_t_r_o_l _o_p_e_r_a_t_o_r. The first word speci- fies the command to be executed. The remaining words are passed as arguments to the invoked command. The return value of a _s_i_m_p_l_e _c_o_m_m_a_n_d is its exit status, or 128+_n if the command is terminated by signal _n. Pipelines A _p_i_p_e_l_i_n_e is a sequence of one or more commands separated by the character |. The format for a pipeline is: [ ! ] _c_o_m_m_a_n_d [ | _c_o_m_m_a_n_d_2 ... ] The standard output of _c_o_m_m_a_n_d is connected to the standard input of _c_o_m_m_a_n_d_2. This connection is performed before any redirections specified by the command (see REDIRECTION below). If the reserved word ! precedes a pipeline, the exit status of that pipeline is the logical NOT of the exit status of the last command. Otherwise, the status of the pipeline is the exit status of the last command. The shell waits for all commands in the pipeline to terminate before returning a value. Each command in a pipeline is executed as a separate process (i.e., in a subshell). Lists A _l_i_s_t is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||, and terminated by one of ;, &, or <newline>. 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 _b_a_c_k_g_r_o_u_n_d in a subshell. GNU Last change: 1995 May 5 3 BASH(1) USER COMMANDS BASH(1) The shell does not wait for the command to finish, and the return status is 0. Commands separated by a ; are executed sequentially; the shell waits for each command to terminate in turn. The return status is the exit status of the last command executed. The control operators && and || denote A