Sprite 1984

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Text File | 1989-01-26 | 24.0 KB | 595 lines

SH User Commands SH NNAAMMEE sh, for, case, if, while, ::, .., break, continue, cd, eval, exec, exit, export, login, read, readonly, set, shift, times, trap, umask, wait - command language SSYYNNOOPPSSIISS sshh [ --cceeiikknnrrssttuuvvxx ] [ arg ] ... DDEESSCCRRIIPPTTIIOONN _S_h is a command programming language that executes commands read from a terminal or a file. See iinnvvooccaattiioonn for the meaning of arguments to the shell. CCoommmmaannddss.. A _s_i_m_p_l_e-_c_o_m_m_a_n_d is a sequence of non blank _w_o_r_d_s separated by blanks (a blank is a ttaabb or a ssppaaccee). The first word specifies the name of the command to be executed. Except as specified below the remaining words are passed as arguments to the invoked command. The command name is passed as argu- ment 0 (see _e_x_e_c_v_e(2)). The _v_a_l_u_e of a simple-command is its exit status if it terminates normally or 200+_s_t_a_t_u_s if it terminates abnormally (see _s_i_g_v_e_c(2) for a list of status values). A _p_i_p_e_l_i_n_e is a sequence of one or more _c_o_m_m_a_n_d_s separated by ||.. The standard output of each command but the last is connected by a _p_i_p_e(2) to the standard input of the next command. Each command is run as a separate process; the shell waits for the last command to terminate. A _l_i_s_t is a sequence of one or more _p_i_p_e_l_i_n_e_s separated by ;;, &&, &&&& or |||| and optionally terminated by ;; or &&. ;; and && have equal precedence which is lower than that of &&&& and ||||, &&&& and |||| also have equal precedence. A semicolon causes sequential execution; an ampersand causes the preceding _p_i_p_e_l_i_n_e to be executed without waiting for it to finish. The symbol &&&& (||||) causes the _l_i_s_t following to be executed only if the preceding _p_i_p_e_l_i_n_e returns a zero (non zero) value. Newlines may appear in a _l_i_s_t, instead of semi- colons, to delimit commands. A _c_o_m_m_a_n_d is either a simple-command or one of the follow- ing. The value returned by a command is that of the last simple-command executed in the command. ffoorr _n_a_m_e [iinn _w_o_r_d ...] ddoo _l_i_s_t ddoonnee Each time a ffoorr command is executed _n_a_m_e is set to the next word in the ffoorr word list. If iinn _w_o_r_d ... is omitted, iinn ""$$@@"" is assumed. Execution ends when there are no more words in the list. ccaassee _w_o_r_d iinn [_p_a_t_t_e_r_n [ || _p_a_t_t_e_r_n ] ... )) _l_i_s_t ;;;;] ... eessaacc Sprite v1.0 May 5, 1986 1 SH User Commands SH A ccaassee command executes the _l_i_s_t associated with the first pattern that matches _w_o_r_d. The form of the pat- terns is the same as that used for file name genera- tion. iiff _l_i_s_t tthheenn _l_i_s_t [eelliiff _l_i_s_t tthheenn _l_i_s_t] ... [eellssee _l_i_s_t] ffii The _l_i_s_t following iiff is executed and if it returns zero the _l_i_s_t following tthheenn is executed. Otherwise, the _l_i_s_t following eelliiff is executed and if its value is zero the _l_i_s_t following tthheenn is executed. Failing that the eellssee _l_i_s_t is executed. wwhhiillee _l_i_s_t [ddoo _l_i_s_t] ddoonnee A wwhhiillee command repeatedly executes the wwhhiillee _l_i_s_t and if its value is zero executes the ddoo _l_i_s_t; otherwise the loop terminates. The value returned by a wwhhiillee command is that of the last executed command in the ddoo _l_i_s_t. uunnttiill may be used in place of wwhhiillee to negate the loop termination test. (( _l_i_s_t )) Execute _l_i_s_t in a subshell. {{ _l_i_s_t }} _l_i_s_t is simply executed. The following words are only recognized as the first word of a command and when not quoted. iiff tthheenn eellssee eelliiff ffii ccaassee iinn eessaacc ffoorr wwhhiillee uunnttiill ddoo ddoonnee {{ }} CCoommmmaanndd ssuubbssttiittuuttiioonn.. The standard output from a command enclosed in a pair of back quotes (````) may be used as part or all of a word; trailing newlines are removed. PPaarraammeetteerr ssuubbssttiittuuttiioonn.. The character $$ is used to introduce substitutable parame- ters. Positional parameters may be assigned values by sseett. Variables may be set by writing _n_a_m_e==_v_a_l_u_e [ _n_a_m_e==_v_a_l_u_e ] ... ${{_p_a_r_a_m_e_t_e_r}} A _p_a_r_a_m_e_t_e_r is a sequence of letters, digits or under- scores (a _n_a_m_e), a digit, or any of the characters ** @@ ## ?? -- $$ !!.. The value, if any, of the parameter is sub- stituted. The braces are required only when _p_a_r_a_m_e_t_e_r is followed by a letter, digit, or underscore that is not to be interpreted as part of its name. If _p_a_r_a_m_e_- _t_e_r is a digit, it is a positional parameter. If Sprite v1.0 May 5, 1986 2 SH User Commands SH _p_a_r_a_m_e_t_e_r is ** or @@ then all the positional parameters, starting with $$11, are substituted separated by spaces. $$00 is set from argument zero when the shell is invoked. ${{_p_a_r_a_m_e_t_e_r-_w_o_r_d}} If _p_a_r_a_m_e_t_e_r is set, substitute its value; otherwise substitute _w_o_r_d. ${{_p_a_r_a_m_e_t_e_r=_w_o_r_d}} If _p_a_r_a_m_e_t_e_r is not set, set it to _w_o_r_d; the value of the parameter is then substituted. Positional parame- ters may not be assigned to in this way. ${{_p_a_r_a_m_e_t_e_r?_w_o_r_d}} If _p_a_r_a_m_e_t_e_r is set, substitute its value; otherwise, print _w_o_r_d and exit from the shell. If _w_o_r_d is omit- ted, a standard message is printed. ${{_p_a_r_a_m_e_t_e_r+_w_o_r_d}} If _p_a_r_a_m_e_t_e_r is set, substitute _w_o_r_d; otherwise substi- tute nothing. In the above _w_o_r_d is not evaluated unless it is to be used as the substituted string. (So that, for example, echo ${d-'pwd'} will only execute _p_w_d if _d is unset.) The following _p_a_r_a_m_e_t_e_r_s are automatically set by the shell. ## The number of positional parameters in decimal. -- Options supplied to the shell on invocation or by sseett. ?? The value returned by the last executed command in decimal. $$ The process number of this shell. !! The process number of the last background command invoked. The following _p_a_r_a_m_e_t_e_r_s are used but not set by the shell. HHOOMMEE The default argument (home directory) for the ccdd command. PPAATTHH The search path for commands (see eexxeeccuuttiioonn). MMAAIILL If this variable is set to the name of a mail file, the shell informs the user of the arrival of mail in the specified file. PPSS11 Primary prompt string, by default '$ '. PPSS22 Secondary prompt string, by default '> '. IIFFSS Internal field separators, normally ssppaaccee, ttaabb, and nneewwlliinnee. IIFFSS is ignored if _s_h is running as root or if the effective user id differs from the real user id. Sprite v1.0 May 5, 1986 3 SH User Commands SH BBllaannkk iinntteerrpprreettaattiioonn.. After parameter and command substitution, any results of substitution are scanned for internal field separator char- acters (those found in $$IIFFSS) and split into distinct argu- ments where such characters are found. Explicit null argu- ments ("" or '') are retained. Implicit null arguments (those resulting from _p_a_r_a_m_e_t_e_r_s that have no values) are removed. FFiillee nnaammee ggeenneerraattiioonn.. Following substitution, each command word is scanned for the characters **, ?? and [[.. If one of these characters appears, the word is regarded as a pattern. The word is replaced with alphabetically sorted file names that match the pat- tern. If no file name is found that matches the pattern, the word is left unchanged. The character .. at the start of a file name or immediately following a //, and the character //, must be matched explicitly. ** Matches any string, including the null string. ?? Matches any single character. [[......]] Matches any one of the characters enclosed. A pair of characters separated by -- matches any character lexi- cally between the pair. QQuuoottiinngg.. The following characters have a special meaning to the shell and cause termination of a word unless quoted. ;; && (( )) || << >> nneewwlliinnee ssppaaccee ttaabb A character may be _q_u_o_t_e_d by preceding it with a \\.. \\nneeww-- lliinnee is ignored. All characters enclosed between a pair of quote marks (''''), except a single quote, are quoted. Inside double quotes ("""") parameter and command substitution occurs and \\ quotes the characters \\ '' "" and $$. ""$$**"" is equivalent to ""$$11 $$22 ......"" whereas ""$$@@"" is equivalent to ""$$11"" ""$$22"" ...... .. PPrroommppttiinngg.. When used interactively, the shell prompts with the value of PS1 before reading a command. If at any time a newline is typed and further input is needed to complete a command, the secondary prompt ($$PPSS22) is issued. IInnppuutt oouuttppuutt.. Before a command is executed its input and output may be redirected using a special notation interpreted by the shell. The following may appear anywhere in a simple- command or may precede or follow a _c_o_m_m_a_n_d and are not Sprite v1.0 May 5, 1986 4 SH User Commands SH passed on to the invoked command. Substitution occurs before _w_o_r_d or _d_i_g_i_t is used. <_w_o_r_d Use file _w_o_r_d as standard input (file descriptor 0). >_w_o_r_d Use file _w_o_r_d as standard output (file descriptor 1). If the file does not exist, it is created; otherwise it is truncated to zero length. >>_w_o_r_d Use file _w_o_r_d as standard output. If the file exists, output is appended (by seeking to the end); otherwise the file is created. <<_w_o_r_d The shell input is read up to a line the same as _w_o_r_d, or end of file. The resulting document becomes the standard input. If any character of _w_o_r_d is quoted, no interpretation is placed upon the characters of the document; otherwise, parameter and command substitution occurs, \\nneewwlliinnee is ignored, and \\ is used to quote the characters \\ $$ '' and the first character of _w_o_r_d. <&_d_i_g_i_t The standard input is duplicated from file descriptor _d_i_g_i_t; see _d_u_p(2). Similarly for the standard output using >. <&- The standard input is closed. Similarly for the stan- dard output using >. If one of the above is preceded by a digit, the file descriptor created is that specified by the digit (instead of the default 0 or 1). For example, ... 2>&1 creates file descriptor 2 to be a duplicate of file descrip- tor 1. If a command is followed by && then the default standard input for the command is the empty file (/dev/null). Other- wise, the environment for the execution of a command con- tains the file descriptors of the invoking shell as modified by input output specifications. EEnnvviirroonnmmeenntt.. The environment is a list of name-value pairs that is passed to an executed program in the same way as a normal argument list; see _e_x_e_c_v_e(2) and _e_n_v_i_r_o_n(7). The shell interacts Sprite v1.0 May 5, 1986 5 SH User Commands SH with the environment in several ways. On invocation, the shell scans the environment and creates a _p_a_r_a_m_e_t_e_r for each name found, giving it the corresponding value. Executed commands inherit the same environment. If the user modifies the values of these _p_a_r_a_m_e_t_e_r_s or creates new ones, none of these affects the environment unless the eexxppoorrtt command is used to bind the shell's _p_a_r_a_m_e_t_e_r to the environment. The environment seen by any executed command is thus composed of any unmodified name-value pairs originally inherited by the shell, plus any modifications or additions, all of which must be noted in eexxppoorrtt commands. The environment for any _s_i_m_p_l_e-_c_o_m_m_a_n_d may be augmented by prefixing it with one or more assignments to _p_a_r_a_m_e_t_e_r_s. Thus these two lines are equivalent TERM=450 cmd args (export TERM; TERM=450; cmd args) If the --kk flag is set, _a_l_l keyword arguments are placed in the environment, even if the occur after the command name. The following prints 'a=b c' and 'c': echo a=b c set -k echo a=b c SSiiggnnaallss.. The INTERRUPT and QUIT signals for an invoked command are ignored if the command is followed by &&; otherwise signals have the values inherited by the shell from its parent. (But see also ttrraapp..) EExxeeccuuttiioonn.. Each time a command is executed the above substitutions are carried out. Except for the 'special commands' listed below a new process is created and an attempt is made to execute the command via an _e_x_e_c_v_e(2). The shell parameter $$PPAATTHH defines the search path for the directory containing the command. Each alternative direc- tory name is separated by a colon (::). The default path is :://bbiinn:://uussrr//bbiinn. If the command name contains a /, the search path is not used. Otherwise, each directory in the path is searched for an executable file. If the file has execute permission but is not an _a._o_u_t file, it is assumed to be a file containing shell commands. A subshell (i.e., a separate process) is spawned to read it. A parenthesized command is also executed in a subshell. SSppeecciiaall ccoommmmaannddss.. The following commands are executed in the shell process and except where specified no input output redirection is Sprite v1.0 May 5, 1986 6 SH User Commands SH permitted for such commands. ## For non-interactive shells, everything following the ## is treated as a comment, i.e. the rest of the line is ignored. For interactive shells, the ## has no special effect. :: No effect; the command does nothing. .. _f_i_l_e Read and execute commands from _f_i_l_e and return. The search path $$PPAATTHH is used to find the directory con- taining _f_i_l_e. bbrreeaakk [_n] Exit from the enclosing ffoorr or wwhhiillee loop, if any. If _n is specified, break _n levels. ccoonnttiinnuuee [_n] Resume the next iteration of the enclosing ffoorr or wwhhiillee loop. If _n is specified, resume at the _n-th enclosing loop. ccdd [_a_r_g] Change the current directory to _a_r_g. The shell parame- ter $$HHOOMMEE is the default _a_r_g. eevvaall [_a_r_g ...] The arguments are read as input to the shell and the resulting command(s) executed. eexxeecc [_a_r_g ...] The command specified by the arguments is executed in place of this shell without creating a new process. Input output arguments may appear and if no other argu- ments are given cause the shell input output to be modified. eexxiitt [_n] Causes a non interactive shell to exit with the exit status specified by _n. If _n is omitted, the exit status is that of the last command executed. (An end of file will also exit from the shell.) eexxppoorrtt [_n_a_m_e ...] The given names are marked for automatic export to the _e_n_v_i_r_o_n_m_e_n_t of subsequently-executed commands. If no arguments are given, a list of exportable names is printed. llooggiinn [_a_r_g ...] Equivalent to 'exec login arg ...'. rreeaadd _n_a_m_e ... One line is read from the standard input; successive words of the input are assigned to the variables _n_a_m_e in order, with leftover words to the last variable. The return code is 0 unless the end-of-file is encoun- tered. rreeaaddoonnllyy [_n_a_m_e ...] The given names are marked readonly and the values of the these names may not be changed by subsequent Sprite v1.0 May 5, 1986 7 SH User Commands SH assignment. If no arguments are given, a list of all readonly names is printed. sseett [--eekknnppttuuvvxx [_a_r_g ...]] --ee If non interactive, exit immediately if a command fails. --kk All keyword arguments are placed in the environment for a command, not just those that precede the com- mand name. --nn Read commands but do not execute them. --tt Exit after reading and executing one command. --uu Treat unset variables as an error when substituting. --vv Print shell input lines as they are read. --xx Print commands and their arguments as they are exe- cuted. -- Turn off the --xx and --vv options. These flags can also be used upon invocation of the shell. The current set of flags may be found in $$--. Remaining arguments are positional parameters and are assigned, in order, to $$11, $$22, etc. If no arguments are given, the values of all names are printed. sshhiifftt The positional parameters from $$22... are renamed $$11... ttiimmeess Print the accumulated user and system times for processes run from the shell. ttrraapp [_a_r_g] [_n] ... _A_r_g is a command to be read and executed when the shell receives signal(s) _n. (Note that _a_r_g is scanned once when the trap is set and once when the trap is taken.) Trap commands are executed in order of signal number. If _a_r_g is absent, all trap(s) _n are reset to their ori- ginal values. If _a_r_g is the null string, this signal is ignored by the shell and by invoked commands. If _n is 0, the command _a_r_g is executed on exit from the shell, otherwise upon receipt of signal _n as numbered in _s_i_g_v_e_c(2). _T_r_a_p with no arguments prints a list of commands associated with each signal number. uummaasskk [ _n_n_n ] The user file creation mask is set to the octal value _n_n_n (see _u_m_a_s_k(2)). If _n_n_n is omitted, the current value of the mask is printed. wwaaiitt [_n] Wait for the specified process and report its termina- tion status. If _n is not given, all currently active child processes are waited for. The return code from Sprite v1.0 May 5, 1986 8 SH User Commands SH this command is that of the process waited for. IInnvvooccaattiioonn.. If the first character of argument zero is --, commands are read from $$HHOOMMEE//..pprrooffiillee, if such a file exists. Commands are then read as described below. The following flags are interpreted by the shell when it is invoked. --cc _s_t_r_i_n_g If the --cc flag is present, commands are read from _s_t_r_i_n_g. --ss If the --ss flag is present or if no arguments remain then commands are read from the standard input. Shell output is written to file descrip- tor 2. --ii If the --ii flag is present or if the shell input and output are attached to a terminal (as told by _g_t_t_y) then this shell is _i_n_t_e_r_a_c_t_i_v_e. In this case the terminate signal SIGTERM (see _s_i_g_v_e_c(2)) is ignored (so that 'kill 0' does not kill an interactive shell) and the interrupt signal SIG- INT is caught and ignored (so that wwaaiitt is inter- ruptible). In all cases SIGQUIT is ignored by the shell. The remaining flags and arguments are described under the sseett command. FFIILLEESS $HOME/..profile /tmp/sh* /dev/null SSEEEE AALLSSOO csh(1), test(1), execve(2), environ(7) DDIIAAGGNNOOSSTTIICCSS Errors detected by the shell, such as syntax errors cause the shell to return a non zero exit status. If the shell is being used non interactively then execution of the shell file is abandoned. Otherwise, the shell returns the exit status of the last command executed (see also eexxiitt). BBUUGGSS If << is used to provide standard input to an asynchronous process invoked by &, the shell gets mixed up about naming the input document. A garbage file /tmp/sh* is created, and the shell complains about not being able to find the file by another name. Sprite v1.0 May 5, 1986 9