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Text File | 1994-07-26 | 40.1 KB | 771 lines

sh(C) 06 January 1993 sh(C) _N_a_m_e sh - invoke the shell command interpreter _S_y_n_t_a_x sshh [ --aacceeiikknnrrssttuuvvxx ] [ _aa_rr_gg_ss ] _D_e_s_c_r_i_p_t_i_o_n The shell is the standard command programming language that executes com- mands read from a terminal or a file. See ``Invocation'' below for the meaning of arguments to the shell. _C_o_m_m_a_n_d_s A _s_i_m_p_l_e-_c_o_m_m_a_n_d is a sequence of nonblank _w_o_r_d_s separated by _b_l_a_n_k_s (a _b_l_a_n_k is a tab or a space). 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 argument 0 (see eexxeecc(S)). The _v_a_l_u_e of a simple-command is its exit status if it terminates normally, or (octal) 1000+_ss_tt_aa_tt_uu_ss if it ter- minates abnormally. See ssiiggnnaall(S) 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 a vertical bar (||). (The caret (^^), is an obsolete synonym for the vertical bar and should not be used in a pipeline. Scripts that use ``^'' for pipelines are incompatible with the Korn shell.) The standard output of each com- mand but the last is connected by a ppiippee(S) 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 pipelines separated by ;;, &&, &&&&, or ||||, and optionally terminated by ;; or &&. Of these four symbols, ;; and && have equal precedence, which is lower than that of &&&& and ||||. The sym- bols &&&& and |||| also have equal precedence. A semicolon (;;) causes sequential execution of the preceding pipeline; an ampersand (&&) causes asynchronous execution of the preceding pipeline (that is, the shell does _n_o_t wait for that pipeline to finish). The symbol &&&& (||||) causes the _l_i_s_t following it to be executed only if the preceding pipeline returns a zero (nonzero) exit status. An arbitrary number of newlines may appear in a _l_i_s_t, instead of semicolons, to delimit commands. A _c_o_m_m_a_n_d is either a simple-command or one of the following commands. Unless otherwise stated, the value returned by a command is that of the last simple-command executed in the command: ffoorr _nn_aa_mm_ee [ iinn _ww_oo_rr_dd ... ] ddoo _ll_ii_ss_tt ddoonnee Each time a ffoorr command is executed, _nn_aa_mm_ee is set to the next _ww_oo_rr_dd taken from the iinn _ww_oo_rr_dd list. If iinn _ww_oo_rr_dd is omitted, then the ffoorr command exe- cutes the ddoo _ll_ii_ss_tt once for each positional parameter that is set (see ``Parameter substitution'' below). Execution ends when there are no more words in the list. ccaassee _ww_oo_rr_dd iinn [ _pp_aa_tt_tt_ee_rr_nn [ | _pp_aa_tt_tt_ee_rr_nn ] ... )) _ll_ii_ss_tt ;;;; ] eessaacc A ccaassee command executes the _ll_ii_ss_tt associated with the first _pp_aa_tt_tt_ee_rr_nn that matches _ww_oo_rr_dd. The form of the patterns is the same as that used for filename generation (see ``Filename generation'' below). iiff _ll_ii_ss_tt tthheenn _ll_ii_ss_tt [ eelliiff _ll_ii_ss_tt tthheenn _ll_ii_ss_tt ] ... [ eellssee _ll_ii_ss_tt ] ffii The _ll_ii_ss_tt following iiff is executed and, if it returns a zero exit status, the _ll_ii_ss_tt following the first tthheenn is executed. Otherwise, the _ll_ii_ss_tt fol- lowing eelliiff is executed and, if its value is zero, the _ll_ii_ss_tt following the next tthheenn is executed. Failing that, the eellssee _ll_ii_ss_tt is executed. If no eellssee _ll_ii_ss_tt or tthheenn _ll_ii_ss_tt is executed, then the iiff command returns a zero exit status. wwhhiillee _ll_ii_ss_tt ddoo _ll_ii_ss_tt ddoonnee A wwhhiillee command repeatedly executes the wwhhiillee _ll_ii_ss_tt and, if the exit status of the last command in the list is zero, executes the ddoo _ll_ii_ss_tt; otherwise the loop terminates. If no commands in the ddoo _ll_ii_ss_tt are exe- cuted, then the wwhhiillee command returns a zero exit status; uunnttiill may be used in place of wwhhiillee to negate the loop termination test. uunnttiill _ll_ii_ss_tt ddoo _ll_ii_ss_tt ddoonnee uunnttiill is similar to wwhhiillee, only uunnttiill continues execution until the first _ll_ii_ss_tt returns a zero exit status. In other words, uunnttiill works until the test condition succeeds (it works the whole time the command is failing); wwhhiillee works until the test condition fails. uunnttiill is useful when you are waiting for a particular event to occur. ((_ll_ii_ss_tt)) Executes _ll_ii_ss_tt in a subshell. {{_ll_ii_ss_tt;;}} _ll_ii_ss_tt is simply executed. _nn_aa_mm_ee (()) {{_ll_ii_ss_tt;;}} Define a function which is referenced by _nn_aa_mm_ee. The body of functions is the _ll_ii_ss_tt of commands between {{ and }}. Execution of functions is described later (see ``Execution''.) The following words are recognized only as the first word of a command and when not quoted: iiff tthheenn eellssee eelliiff ffii ccaassee eessaacc ffoorr wwhhiillee uunnttiill ddoo ddoonnee {{ }} _C_o_m_m_e_n_t_s A word beginning with ## causes that word and all the following characters up to a newline to be ignored. _C_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n The standard output from a command enclosed between grave accents ( `` `` ) may be used as part or all of a word; trailing newlines are removed. No interpretation is done on the command string before the string is read, except to remove backslashes (\\) used to escape other characters. Backslashes may be used to escape grave accents (``) or other backslashes and are removed before the command string is read. Escaping grave accents allows nested command substitution. If the command substitution lies within a pair of double quotes ( "" `` ...... `` "" ), backslashes used to escape a double quote (\\"") will be removed; otherwise, they will be left intact. If a backslash is used to escape a newline character, both the backslash and the newline are removed (see the section on ``Quoting''). In addi- tion, backslashes used to escape dollar signs ( \\$$ ) are removed. Since no interpretation is done on the command string before it is read, inserting a backslash to escape a dollar sign has no effect. Backslashes that precede characters other than \\, ``, "", nneewwlliinnee, and $$ are left intact. _P_a_r_a_m_e_t_e_r _s_u_b_s_t_i_t_u_t_i_o_n The character $$ is used to introduce substitutable _p_a_r_a_m_e_t_e_r_s. There are two types of parameters, positional and keyword. If _p_a_r_a_m_e_t_e_r is a digit, it is a positional parameter. Positional parameters may be assigned values by sseett. Keyword parameters, (also known as variables) may be assigned values by writing: _nn_aa_mm_ee _== _vv_aa_ll_uu_ee [ _nn_aa_mm_ee _== _vv_aa_ll_uu_ee ] ... Pattern-matching is not performed on _vv_aa_ll_uu_ee. There cannot be a function and a variable with the same name. $${{_pp_aa_rr_aa_mm_ee_tt_ee_rr}} A _pp_aa_rr_aa_mm_ee_tt_ee_rr is a sequence of letters, digits, or underscores (a _n_a_m_e), a digit, or any of the characters **, @@, ##, ??, --, $$, and !!. The value, if any, of the parameter is substituted. The braces are required only when _pp_aa_rr_aa_mm_ee_tt_ee_rr is followed by a letter, digit, or underscore that is not to be interpreted as part of its name. A _n_a_m_e must begin with a letter or underscore. If _pp_aa_rr_aa_mm_ee_tt_ee_rr is a digit then it is a positional parameter. If _pp_aa_rr_aa_mm_ee_tt_ee_rr is ** or @@, then all the positional parameters, starting with $$11, are substi- tuted (separated by spaces). Parameter $$00 is set from argument zero when the shell is invoked. $${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::--_ww_oo_rr_dd}} If _pp_aa_rr_aa_mm_ee_tt_ee_rr is set and is not a null argument, substitute its value; otherwise substitute _ww_oo_rr_dd. $${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::==_ww_oo_rr_dd}} If _pp_aa_rr_aa_mm_ee_tt_ee_rr is not set or is null, then set it to _ww_oo_rr_dd; the value of the parameter is then substituted. Positional parameters may not be assigned to in this way. $${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::??_ww_oo_rr_dd}} If _pp_aa_rr_aa_mm_ee_tt_ee_rr is set and is not a null argument, substitute its value; otherwise, print _ww_oo_rr_dd and exit from the shell. If _ww_oo_rr_dd is omitted, the message ``parameter null or not set'' is printed. $${{_pp_aa_rr_aa_mm_ee_tt_ee_rr::++_ww_oo_rr_dd}} If _pp_aa_rr_aa_mm_ee_tt_ee_rr is set and is not a null argument, substitute _ww_oo_rr_dd; otherwise substitute nothing. In the above, _ww_oo_rr_dd is not evaluated unless it is to be used as the sub- stituted string, so that in the following example, ppwwdd is executed only if dd is not set or is null: eecchhoo $${{dd::--((ggaappwwdd``}} If the colon (::) is omitted from the above expressions, then the shell only checks whether _pp_aa_rr_aa_mm_ee_tt_ee_rr is set. The following parameters are automatically set by the shell: ## The number of positional parameters in decimal -- Flags supplied to the shell on invocation or by the sseett command ?? The decimal value returned by the last synchronously executed com- mand $$ The process number of this shell !! The process number of the last background command invoked The following parameters are used by the shell: CCDDPPAATTHH Defines search path for the ccdd command. See the section ``cd'' under ``Special commands'' below. HHOOMMEE The default argument (home directory) for the ccdd command PPAATTHH The search path for commands (see ``Execution'' below) MMAAIILL If this variable is set to the name of a mail file, then the shell informs the user of the arrival of mail in the specified file MMAAIILLCCHHEECCKK This parameter specifies how often (in seconds) the shell will check for the arrival of mail in the files specified by the MMAAIILLPPAATTHH or MMAAIILL parameters. The default value is 600 seconds (10 minutes). If set to 0, the shell will check before each prompt. MMAAIILLPPAATTHH A colon ((::)) separated list of filenames. If this parameter is set, the shell informs the user of the arrival of mail in any of the specified files. Each filename can be fol- lowed by ``%'' and a message that will be printed when the modification time changes. The default message is ``you have mail''. PPSS11 Primary prompt string, by default ``$$ '' PPSS22 Secondary prompt string, by default ``>> '' IIFFSS Internal field separators, normally ssppaaccee, ttaabb, and nneewwlliinnee SSHHEELLLL When the shell is invoked, it scans the environment (see ``Environment'' below) for this name. If it is found and there is an `r' in the file name part of its value, the shell becomes a restricted shell. The shell gives default values to PPAATTHH, PPSS11, PPSS22, and IIFFSS, while HHOOMMEE and MMAAIILL are not set at all by the shell (although HHOOMMEE _i_s set by llooggiinn(M)). _B_l_a_n_k _i_n_t_e_r_p_r_e_t_a_t_i_o_n After parameter and command substitution, the results of substitution are scanned for internal field separator characters (those found in IIFFSS) and split into distinct arguments where such characters are found. Explicit null arguments ( """" or '''' ) are retained. Implicit null arguments (those resulting from _pp_aa_rr_aa_mm_ee_tt_ee_rr_ss that have no values) are removed. _F_i_l_e_n_a_m_e _g_e_n_e_r_a_t_i_o_n Following substitution, each command _ww_oo_rr_dd is scanned for the characters **, ??, and [[. If one of these characters appears, the word is regarded as a _pp_aa_tt_tt_ee_rr_nn. The word is replaced with alphabetically sorted filenames that match the pattern. If no filename is found that matches the pat- tern, the word is left unchanged. The character ``.'' at the start of a filename or immediately following a ``/'', as well as the character ``/'' itself, must be matched explicitly. These characters and their matching patterns are: ** Matches any string, including the null string. ?? Matches any single character. [[...]] Matches any one of the enclosed characters. A pair of characters separated by ``-'' matches any character lexically between the pair, inclusive. If the first character following the opening bracket ([[) is an exclamation mark (!!), then any character not enclosed is matched. _Q_u_o_t_i_n_g The following characters have a special meaning to the shell and cause termination of a word unless quoted: ; & ( ) | ^ < > newline space tab A character may be _q_u_o_t_e_d (that is, made to stand for itself) by preced- ing it with a ``\''. The pair \\nneewwlliinnee is ignored. All characters enclosed between a pair of single quotation marks ('' ''), except a single quotation mark, are quoted. Inside double quotation marks ("" ""), parame- ter and command substitution occurs and ``\'' quotes the characters \\, ``, "", and $$. ""$$**"" is equivalent to ""$$11 $$22 ..."", whereas ""$$@@"" is equivalent to ""$$11"" ""$$22"" ... _P_r_o_m_p_t_i_n_g When used interactively, the shell prompts with the value of PPSS11 before reading a command. If at any time a newline is typed and further input is needed to complete a command, the secondary prompt (that is, the value of PPSS22) is issued. _S_p_e_l_l_i_n_g _c_h_e_c_k_e_r When using ccdd(C) the shell checks spelling. For example, if you change to a different directory using ccdd and misspell the directory name, the shell responds with an alternative spelling of an existing directory. Enter ``y'' and press <Return> (or just press <Return>) to change to the offered directory. If the offered spelling is incorrect, enter ``n'', then retype the command line. In this example the sshh(C) response is boldfaced: $ cd /usr/spol/uucp ccdd //uussrr//ssppooooll//uuuuccpp??y ookk _I_n_p_u_t/_O_u_t_p_u_t 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 command. They are _n_o_t passed on to the invoked command; substitution occurs before _ww_oo_rr_dd or _dd_ii_gg_ii_tt is used: <<_ww_oo_rr_dd Use file _ww_oo_rr_dd as standard input (file descriptor 0). >>_ww_oo_rr_dd Use file _ww_oo_rr_dd as standard output (file descriptor 1). If the file does not exist, it is created; otherwise, it is truncated to zero length. >>>>_ww_oo_rr_dd Use file _ww_oo_rr_dd as standard output. If the file exists, out- put is appended to it (by first seeking the end-of-file); otherwise, the file is created. <<<<[--]_ww_oo_rr_dd The shell input is read up to a line that is the same as _ww_oo_rr_dd, or to an end-of-file. The resulting document becomes the standard input. If any character of _ww_oo_rr_dd is quoted, no interpretation is placed upon the characters of the docu- ment; otherwise, parameter and command substitution occurs, (unescaped) \\nneewwlliinnee is ignored, and ``\'' must be used to quote the characters \\, $$, ``, and the first character of _ww_oo_rr_dd. If ``-'' is appended to <<<<, all leading tabs are stripped from _ww_oo_rr_dd and from the document. <<&&_dd_ii_gg_ii_tt The standard input is duplicated from file descriptor _dd_ii_gg_ii_tt (see dduupp(S)). Similarly for the standard output using >>. <<&&-- The standard input is closed. Similarly for the standard 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: ...... 22>>&&11 creates file descriptor 2 that is a duplicate of file descriptor 1. If a command is followed by ``&'', the default standard input for the command is the empty file /_d_e_v/_n_u_l_l. Otherwise, the environment for the execution of a command contains the file descriptors of the invoking shell as modified by input/output specifications. _E_n_v_i_r_o_n_m_e_n_t The _e_n_v_i_r_o_n_m_e_n_t (see eennvviirroonn(M)) is a list of name-value pairs that is passed to an executed program in the same way as a normal argument list. The shell interacts with the environment in several ways. On invocation, the shell scans the environment and creates a parameter for each name found, giving it the corresponding value. Executed commands inherit the same environment. If the user modifies the values of these parameters or creates new ones, none of these affect the environment unless the eexxppoorrtt command is used to bind the shell's parameter to the environment. The environment seen by any executed command is composed of any unmodified name-value pairs originally inherited by the shell, minus any pairs removed by uunnsseett, 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 parameters. Thus: TTEERRMM==wwyy6600 _cc_mm_dd _aa_rr_gg_ss and (eexxppoorrtt TTEERRMM; TTEERRMM==wwyy6600; _cc_mm_dd _aa_rr_gg_ss) are equivalent (as far as the above execution of _cc_mm_dd is concerned). If the --kk flag is set, _a_l_l keyword arguments are placed in the environ- ment, even if they occur after the command name. _S_i_g_n_a_l_s The IINNTTEERRRRUUPPTT and QQUUIITT 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, with the exception of signal 11. See the ttrraapp command below. _E_x_e_c_u_t_i_o_n Each time a command is executed, the above substitutions are carried out. If the command name does not match a _s_p_e_c_i_a_l _c_o_m_m_a_n_d, but matches the name of a defined function, the function is executed in the shell process (note how this differs from the execution of shell procedures). The posi- tional parameters $$11,, $$22, ... are set to the arguments of the function. If the command name matches neither a _s_p_e_c_i_a_l _c_o_m_m_a_n_d nor the name of a defined function, a new process is created and an attempt is made to exe- cute the command via eexxeecc(S). The shell parameter PPAATTHH defines the search path for the directory con- taining the command. Alternative directory names are separated by a colon (::). The default path is :/_b_i_n:/_u_s_r/_b_i_n (specifying the current directory, /_b_i_n, and /_u_s_r/_b_i_n, in that order). Note that the current directory is specified by a null pathname, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If the command name contains a ``/'', then the search path is not used. Otherwise, each directory in the path is searched for an exe- cutable 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 (that is, a separate process) is spawned to read it. A parenthesized command is also executed in a subshell. Shell procedures are often used by users running the ccsshh. However, if the first character of the procedure is a ``#'' (comment character), ccsshh assumes the procedure is a ccsshh script, and invokes //bbiinn//ccsshh to execute it. Always start sshh procedures with some other character if ccsshh users are to run the procedure at any time. This invokes the standard shell //bbiinn//sshh. The location in the search path where a command was found is remembered by the shell (to help avoid unnecessary eexxeeccs later). If the command was found in a relative directory, its location must be re-determined when- ever the current directory changes. The shell forgets all remembered locations whenever the PPAATTHH variable is changed or the hhaasshh --rr command is executed (see hhaasshh in next section). _S_p_e_c_i_a_l _c_o_m_m_a_n_d_s Input/output redirection is permitted for these commands: :: No effect; the command does nothing. A zero exit code is returned. .. _ff_ii_ll_ee Reads and executes commands from _ff_ii_ll_ee and returns. The search path specified by PPAATTHH is used to find the directory containing _ff_ii_ll_ee. bbrreeaakk [ _nn ] Exits from the enclosing ffoorr, wwhhiillee, or uunnttiill loop, if any. If _nn is specified, it breaks _nn levels. ccoonnttiinnuuee [ _nn ] Resumes the next iteration of the enclosing ffoorr, wwhhiillee, or uunnttiill loop. If _nn is specified, it resumes at the _nn-th enclosing loop. ccdd [ _aa_rr_gg ] Changes the current directory to _aa_rr_gg. The shell parameter HHOOMMEE is the default _aa_rr_gg. The shell parameter CCDDPPAATTHH defines the search path for the directory containing _aa_rr_gg. Alternative directory names are separated by a colon (:). The default path is <null> (specifying the current directory). Note that the current directory is speci- fied by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If _aa_rr_gg begins with a ``/'', the search path is not used. Otherwise, each directory in the path is searched for _aa_rr_gg. If the shell is reading its commands from a terminal, and the speci- fied directory does not exist (or some component cannot be searched), spelling correction is applied to each component of _d_i_r_e_c_t_o_r_y, in a search for the ``correct'' name. The shell then asks whether or not to try and change directory to the corrected directory name; an answer of nn means ``no'', and anything else is taken as ``yes''. eecchhoo [ _aa_rr_gg ] Writes arguments separated by blanks and terminated by a newline on the standard output. Arguments may be enclosed in quotes. Quotes are required so that the shell correctly interprets these special escape sequences: \\bb Backspace \\cc Prints line without newline. \\ff Form feed \\nn Newline \\rr Carriage return \\tt Tab \\vv Vertical tab \\\\ Backslash \\_nn The 8-bit character whose ASCII code is the 1, 2 or 3-digit octal number _nn. _nn must start with a zero. eevvaall [ _aa_rr_gg ... ] The arguments are read as input to the shell and the resulting command(s) executed. eexxeecc [ _aa_rr_gg ... ] 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 arguments are given, cause the shell input/output to be modified. eexxiitt [ _nn ] Causes the shell to exit with the exit status specified by _nn. If _nn is omitted, the exit status is that of the last command executed. An end-of-file will also cause the shell to exit. eexxppoorrtt [ _nn_aa_mm_ee ... ] The given _nn_aa_mm_ees 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 all names that are exported in this shell is printed. ggeettooppttss Used in shell scripts to support command syntax standards (see IInnttrroo(C)); it parses positional parameters and checks for legal options. See ggeettooppttss(C) for usage and description. hhaasshh [ --rr ] [ _nn_aa_mm_ee ... ] For each _nn_aa_mm_ee, the location in the search path of the command speci- fied by _nn_aa_mm_ee is determined and remembered by the shell. The --rr option causes the shell to forget all remembered locations. If no arguments are given, information about remembered commands is presented. ``Hits'' is the number of times a command has been invoked by the shell process. ``Cost'' is a measure of the work required to locate a command in the search path. There are certain situations which require that the stored location of a command be recalculated. Commands for which this will be done are indicated by an asterisk (**) adjacent to the ``hits'' information. ``Cost'' will be incremented when the recalculation is done. nneewwggrrpp [ _aa_rr_gg ... ] Equivalent to eexxeecc nneewwggrrpp _aa_rr_gg ... ppwwdd Print the current working directory. See ppwwdd(C) for usage and description. rreeaadd [ _nn_aa_mm_ee ... ] One line is read from the standard input and the first word is assigned to the first _nn_aa_mm_ee, the second word to the second _nn_aa_mm_ee, etc., with leftover words assigned to the last _nn_aa_mm_ee. The return code is 0 unless an end-of-file is encountered. rreeaaddoonnllyy [ _nn_aa_mm_ee ... ] The given _nn_aa_mm_ees are marked rreeaaddoonnllyy and the values of these _nn_aa_mm_ees may not be changed by subsequent assignment. If no arguments are given, a list of all rreeaaddoonnllyy names is printed. rreettuurrnn [ _nn ] Causes a function to exit with the return value specified by _nn. If _nn is omitted, the return status is that of the last command executed. sseett [ --aaeeffhhkknnuuvvxx [ _aa_rr_gg ... ] ] --aa Mark variables which are modified or created for export. --ee If the shell is noninteractive, exits immediately if a command exits with a nonzero exit status. --ff Disables filename generation. --hh Locates and remembers function commands as functions are defined (function commands are normally located when the function is executed). For example, if hh is set, /_b_i_n/_t_t_y is added to the hash table when: showtty(){ tty } is declared. If hh is unset, the function is not added to the hash table until showtty is called. --kk Places all keyword arguments in the environment for a command, not just those that precede the command name. --nn Reads commands but does not execute them. --uu Treats unset variables as an error when substituting. --vv Prints shell input lines as they are read. --xx Prints commands and their arguments as they are executed. Although this flag is passed to subshells, it does not enable tracing in those subshells. ---- Does not change any of the flags; useful in setting $1 to ``-''. Using ``+'' rather than ``-'' causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags may be found in $$--. The remaining arguments are positional parameters and are assigned, in order, to $$11, $$22, ... If no arguments are given, the values of all names are printed. sshhiifftt [_nn] The positional parameters from $$22 ... are renamed $$11 ... If _nn is specified, shift the positional parameters by _nn places. sshhiifftt is the only way to access positional parameters above $$99. tteesstt Evaluates conditional expressions. See tteesstt(C) for usage and description. ttiimmeess Prints the accumulated user and system times for processes run from the shell. ttrraapp [ _aa_rr_gg ] [ _nn ] ... _aa_rr_gg is a command to be read and executed when the shell receives signal(s) _nn. (Note that _aa_rr_gg is scanned once when the trap is set and once when the trap is taken.) Trap commands are executed in order of signal number. The highest signal number allowed is 16. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. An attempt to trap on signal 11 (memory fault) produces an error. If _aa_rr_gg is absent, all trap(s) _nn are reset to their original values. If _aa_rr_gg is the null string, this signal is ignored by the shell and by the commands it invokes. If _nn is 0, the command _aa_rr_gg is executed on exit from the shell. The ttrraapp command with no arguments prints a list of commands associated with each signal number. ttyyppee [ _nn_aa_mm_ee ... ] For each _nn_aa_mm_ee, indicate how it would be interpreted if used as a command name. uulliimmiitt [ _nn ] imposes a size limit of _nn blocks on files written by the shell and its child processes (files of any size may be read). Any user may decrease the file size limit, but only the super user (_r_o_o_t) can increase the limit. With no argument, the current limit is printed. If no option is given and a number is specified, --ff is assumed. uunnsseett [ _nn_aa_mm_ee ... ] For each _nn_aa_mm_ee, remove the corresponding variable or function. The variables PPAATTHH, PPSS11, PPSS22, MMAAIILLCCHHEECCKK and IIFFSS cannot be unset. uummaasskk [ _oo_oo_oo ] The user file-creation mask is set to the octal number _oo_oo_oo where _oo is an octal digit (see uummaasskk(C)). If _oo_oo_oo is omitted, the current value of the mask is printed. wwaaiitt [ _nn ] Waits for the specified process to terminate, and reports the termi- nation status. If _nn is not given, all currently active child pro- cesses are waited for. The return code from this command is always 0. _I_n_v_o_c_a_t_i_o_n If the shell is invoked through eexxeecc(S) and the first character of argu- ment 0 is ``-'', commands are initially read from /_e_t_c/_p_r_o_f_i_l_e and then from $$HHOOMMEE/._p_r_o_f_i_l_e, if such files exist. Thereafter, commands are read as described below, which is also the case when the shell is invoked as //bbiinn//sshh. The flags below are interpreted by the shell on invocation only; note that unless the --cc or --ss flag is specified, the first argument is assumed to be the name of a file containing commands, and the remain- ing arguments are passed as positional parameters to that command file: --cc _ss_tt_rr_ii_nn_gg If the --cc flag is present, commands are read from _ss_tt_rr_ii_nn_gg. --ss If the --ss flag is present or if no arguments remain, commands are read from the standard input. Any remaining arguments specify the positional parameters. Shell output is written to file descriptor 2. --tt If the --tt flag is present, a single command is read and exe- cuted, and the shell exits. This flag is intended for use by C programs only and is not useful interactively. --ii If the --ii flag is present or if the shell input and output are attached to a terminal, this shell is _i_n_t_e_r_a_c_t_i_v_e. In this case, TTEERRMMIINNAATTEE is ignored (so that kkiillll 00 does not kill an interactive shell) and IINNTTEERRRRUUPPTT is caught and ignored (so that wwaaiitt is interruptible). In all cases, QQUUIITT is ignored by the shell. --rr If the --rr flag is present, the shell is a restricted shell (see rrsshh(C)). The remaining flags and arguments are described under the sseett command above. _E_x_i_t _s_t_a_t_u_s Errors detected by the shell, such as syntax errors, cause the shell to return a nonzero exit status. If the shell is being used noninterac- tively, execution of the shell file is abandoned. Otherwise, the shell returns the exit status of the last command executed. See the eexxiitt com- mand above. _F_i_l_e_s /_e_t_c/_p_r_o_f_i_l_e system default _p_r_o_f_i_l_e, read by login shells before $$HHOOMMEE/._p_r_o_f_i_l_e $$HHOOMMEE/._p_r_o_f_i_l_e read by login shell at login /_t_m_p/_s_h* temporary file for <<<< /_d_e_v/_n_u_l_l source of empty file _S_e_e _a_l_s_o aa..oouutt(FP), ccdd(C), dduupp(S), eennvv(C), eennvviirroonn(M), eexxeecc(S), ffoorrkk(S), kksshh(C), llooggiinn(M), nneewwggrrpp(C), ppiippee(S), pprrooffiillee(M), rrsshh(C), ssiiggnnaall(S), tteesstt(C), uummaasskk(C), uummaasskk(S) and wwaaiitt(S). _N_o_t_e_s The command rreeaaddoonnllyy (without arguments) produces the same type of output as the command eexxppoorrtt. 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 /_t_m_p/_s_h* is created and the shell complains about not being able to find that file by another name. If a command is executed, and a command with the same name is installed in a directory in the search path before the directory where the original command was found, the shell will continue to eexxeecc the original command. Use the hhaasshh command to correct this situation. If you move the current directory or one above it, ppwwdd may not give the correct response. Use the ccdd command with a full pathname to correct this situation. When a sshh user logs in, the system reads and executes commands in /_e_t_c/_p_r_o_f_i_l_e before executing commands in the user's $$HHOOMMEE/._p_r_o_f_i_l_e. You can, therefore, modify the environment for all sshh users on the system by editing /_e_t_c/_p_r_o_f_i_l_e. The shell doesn't treat the high (eighth) bit in the characters of a com- mand line argument specially, nor does it strip the eighth bit from the characters of error messages. Previous versions of the shell used the eighth bit as a quoting mechanism. Existing programs that set the eighth bit of characters in order to quote them as part of the shell command line should be changed to use of the standard shell quoting mechanisms (see the section on ``Quoting''). Words used to specify filenames in input/output redirection are not expanded for filename generation (see the section on ``Filename generation''). For example, ccaatt ffiillee11 >> aa** will create a file named _a*. Because commands in pipelines are run as separate processes, variables set in a pipeline have no effect on the parent shell. If you get the error message: fork failed - too many processes try using the wwaaiitt(C) command to clean up your background processes. If this doesn't help, the system process table is probably full or you have too many active foreground processes (there is a limit to the number of processes that be can associated with your login, and the number the sys- tem can keep track of). _W_a_r_n_i_n_g_s Not all processes of a 3 or more stage pipeline are children of the shell, and thus cannot be waited for. For wwaaiitt _nn, if _nn is not an active process id, all your shell's currently active background processes are waited for and the return code will be zero. _S_t_a_n_d_a_r_d_s _c_o_n_f_o_r_m_a_n_c_e sshh is conformant with: AT&T SVID Issue 2; and X/Open Portability Guide, Issue 3, 1989.