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CSH User Commands CSH NNAAMMEE csh - a shell (command interpreter) with C-like syntax SSYYNNOOPPSSIISS ccsshh [ --cceeffiinnssttvvVVxxXX ] [ arg ... ] DDEESSCCRRIIPPTTIIOONN _C_s_h is a first implementation of a command language inter- preter incorporating a history mechanism (see HHiissttoorryy SSuubb-- ssttiittuuttiioonnss), job control facilities (see JJoobbss), interactive file name and user name completion (see FFiillee NNaammee CCoommppllee-- ttiioonn), and a C-like syntax. So as to be able to use its job control facilities, users of _c_s_h must (and automatically) use the new tty driver fully described in _t_t_y(4). This new tty driver allows generation of interrupt characters from the keyboard to tell jobs to stop. See _s_t_t_y(1) for details on setting options in the new tty driver. An instance of _c_s_h begins by executing commands from the file `.cshrc' in the _h_o_m_e directory of the invoker. If this is a login shell then it also executes commands from the file `.login' there. It is typical for users on crt's to put the command ``stty crt'' in their ._l_o_g_i_n file, and to also invoke _t_s_e_t(1) there. In the normal case, the shell will then begin reading com- mands from the terminal, prompting with `% '. Processing of arguments and the use of the shell to process files contain- ing command scripts will be described later. The shell then repeatedly performs the following actions: a line of command input is read and broken into _w_o_r_d_s. This sequence of words is placed on the command history list and then parsed. Finally each command in the current line is executed. When a login shell terminates it executes commands from the file `.logout' in the users home directory. LLeexxiiccaall ssttrruuccttuurree The shell splits input lines into words at blanks and tabs with the following exceptions. The characters `&' `|' `;' `<' `>' `(' `)' form separate words. If doubled in `&&', `||', `<<' or `>>' these pairs form single words. These parser metacharacters may be made part of other words, or prevented their special meaning, by preceding them with `\'. A newline preceded by a `\' is equivalent to a blank. In addition strings enclosed in matched pairs of quotations, `'', ``' or `"', form parts of a word; metacharacters in these strings, including blanks and tabs, do not form Sprite v1.0 April 24, 1988 1 CSH User Commands CSH separate words. These quotations have semantics to be described subsequently. Within pairs of `'' or `"' charac- ters a newline preceded by a `\' gives a true newline char- acter. When the shell's input is not a terminal, the character `#' introduces a comment which continues to the end of the input line. It is prevented this special meaning when preceded by `\' and in quotations using ``', `'', and `"'. CCoommmmaannddss A simple command is a sequence of words, the first of which specifies the command to be executed. A simple command or a sequence of simple commands separated by `|' characters forms a pipeline. The output of each command in a pipeline is connected to the input of the next. Sequences of pipe- lines may be separated by `;', and are then executed sequen- tially. A sequence of pipelines may be executed without immediately waiting for it to terminate by following it with an `&'. Any of the above may be placed in `(' `)' to form a simple command (which may be a component of a pipeline, etc.) It is also possible to separate pipelines with `||' or `&&' indi- cating, as in the C language, that the second is to be exe- cuted only if the first fails or succeeds respectively. (See _E_x_p_r_e_s_s_i_o_n_s.) JJoobbss The shell associates a _j_o_b with each pipeline. It keeps a table of current jobs, printed by the _j_o_b_s command, and assigns them small integer numbers. When a job is started asynchronously with `&', the shell prints a line which looks like: [1] 1234 indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234. If you are running a job and wish to do something else you may hit the key ^^ZZ (control-Z) which sends a STOP signal to the current job. The shell will then normally indicate that the job has been `Stopped', and print another prompt. You can then manipulate the state of this job, putting it in the background with the _b_g command, or run some other commands and then eventually bring the job back into the foreground with the foreground command _f_g. A ^^ZZ takes effect immedi- ately and is like an interrupt in that pending output and Sprite v1.0 April 24, 1988 2 CSH User Commands CSH unread input are discarded when it is typed. There is another special key ^^YY which does not generate a STOP signal until a program attempts to _r_e_a_d(2) it. This can usefully be typed ahead when you have prepared some commands for a job which you wish to stop after it has read them. A job being run in the background will stop if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giv- ing the command ``stty tostop''. If you set this tty option, then background jobs will stop when they try to pro- duce output like they do when they try to read input. There are several ways to refer to jobs in the shell. The character `%' introduces a job name. If you wish to refer to job number 1, you can name it as `%1'. Just naming a job brings it to the foreground; thus `%1' is a synonym for `fg %1', bringing job 1 back into the foreground. Similarly saying `%1 &' resumes job 1 in the background. Jobs can also be named by prefixes of the string typed in to start them, if these prefixes are unambiguous, thus `%ex' would normally restart a suspended _e_x(1) job, if there were only one suspended job whose name began with the string `ex'. It is also possible to say `%?string' which specifies a job whose text contains _s_t_r_i_n_g, if there is only one such job. The shell maintains a notion of the current and previous jobs. In output pertaining to jobs, the current job is marked with a `+' and the previous job with a `-'. The abbreviation `%+' refers to the current job and `%-' refers to the previous job. For close analogy with the syntax of the _h_i_s_t_o_r_y mechanism (described below), `%%' is also a synonym for the current job. SSttaattuuss rreeppoorrttiinngg This shell learns immediately whenever a process changes state. It normally informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. If, however, you set the shell variable _n_o_t_i_f_y, the shell will notify you immedi- ately of changes of status in background jobs. There is also a shell command _n_o_t_i_f_y which marks a single process so that its status changes will be immediately reported. By default _n_o_t_i_f_y marks the current process; simply say `notify' after starting a background job to mark it. When you try to leave the shell while jobs are stopped, you will be warned that `You have stopped jobs.' You may use the _j_o_b_s command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a Sprite v1.0 April 24, 1988 3 CSH User Commands CSH second time, and the suspended jobs will be terminated. FFiillee NNaammee CCoommpplleettiioonn When the file name completion feature is enabled by setting the shell variable _f_i_l_e_c (see sseett), _c_s_h will interactively complete file names and user names from unique prefixes, when they are input from the terminal followed by the escape character (the escape key, or control-[). For example, if the current directory looks like DSC.OLD bin cmd lib xmpl.c DSC.NEW chaosnet cmtest mail xmpl.o bench class dev mbox xmpl.out and the input is % vi ch<escape> _c_s_h will complete the prefix ``ch'' to the only matching file name ``chaosnet'', changing the input line to % vi chaosnet However, given % vi D<escape> _c_s_h will only expand the input to % vi DSC. and will sound the terminal bell to indicate that the expan- sion is incomplete, since there are two file names matching the prefix ``D''. If a partial file name is followed by the end-of-file char- acter (usually control-D), then, instead of completing the name, _c_s_h will list all file names matching the prefix. For example, the input % vi D<control-D> causes all files beginning with ``D'' to be listed: DSC.NEW DSC.OLD while the input line remains unchanged. The same system of escape and end-of-file can also be used to expand partial user names, if the word to be completed (or listed) begins with the character ``~''. For example, typing cd ~ro<escape> may produce the expansion cd ~root The use of the terminal bell to signal errors or multiple matches can be inhibited by setting the variable _n_o_b_e_e_p. Normally, all files in the particular directory are candi- dates for name completion. Files with certain suffixes can be excluded from consideration by setting the variable _f_i_g_- _n_o_r_e to the list of suffixes to be ignored. Thus, if _f_i_g_- _n_o_r_e is set by the command % set fignore = (.o .out) Sprite v1.0 April 24, 1988 4 CSH User Commands CSH then typing % vi x<escape> would result in the completion to % vi xmpl.c ignoring the files "xmpl.o" and "xmpl.out". However, if the only completion possible requires not ignoring these suf- fixes, then they are not ignored. In addition, _f_i_g_n_o_r_e does not affect the listing of file names by control-D. All files are listed regardless of their suffixes. SSuubbssttiittuuttiioonnss We now describe the various transformations the shell per- forms on the input in the order in which they occur. HHiissttoorryy ssuubbssttiittuuttiioonnss History substitutions place words from previous command input as portions of new commands, making it easy to repeat commands, repeat arguments of a previous command in the current command, or fix spelling mistakes in the previous command with little typing and a high degree of confidence. History substitutions begin with the character `!' and may begin aannyywwhheerree in the input stream (with the proviso that they ddoo nnoott nest.) This `!' may be preceded by an `\' to prevent its special meaning; for convenience, a `!' is passed unchanged when it is followed by a blank, tab, new- line, `=' or `('. (History substitutions also occur when an input line begins with `^'. This special abbreviation will be described later.) Any input line which contains history substitution is echoed on the terminal before it is executed as it could have been typed without history substitution. Commands input from the terminal which consist of one or more words are saved on the history list. The history sub- stitutions reintroduce sequences of words from these saved commands into the input stream. The size of which is con- trolled by the _h_i_s_t_o_r_y variable; the previous command is always retained, regardless of its value. Commands are num- bered sequentially from 1. For definiteness, consider the following output from the _h_i_s_t_o_r_y command: 9 write michael 10 ex write.c 11 cat oldwrite.c 12 diff *write.c The commands are shown with their event numbers. It is not usually necessary to use event numbers, but the current event number can be made part of the _p_r_o_m_p_t by placing an Sprite v1.0 April 24, 1988 5 CSH User Commands CSH `!' in the prompt string. With the current event 13 we can refer to previous events by event number `!11', relatively as in `!-2' (referring to the same event), by a prefix of a command word as in `!d' for event 12 or `!wri' for event 9, or by a string contained in a word in the command as in `!?mic?' also referring to event 9. These forms, without further modification, simply rein- troduce the words of the specified events, each separated by a single blank. As a special case `!!' refers to the previ- ous command; thus `!!' alone is essentially a _r_e_d_o. To select words from an event we can follow the event specification by a `:' and a designator for the desired words. The words of an input line are numbered from 0, the first (usually command) word being 0, the second word (first argument) being 1, etc. The basic word designators are: 0 first (command) word _n _n'th argument ^ first argument, i.e. `1' $ last argument % word matched by (immediately preceding) ?_s? search _x-_y range of words -_y abbreviates `0-_y' * abbreviates `^-$', or nothing if only 1 word in event _x* abbreviates `_x-$' _x- like `_x*' but omitting word `$' The `:' separating the event specification from the word designator can be omitted if the argument selector begins with a `^', `$', `*' `-' or `%'. After the optional word designator can be placed a sequence of modifiers, each pre- ceded by a `:'. The following modifiers are defined: h Remove a trailing pathname component, leaving the head. r Remove a trailing `.xxx' component, leaving the root name. e Remove all but the extension `.xxx' part. s/_l/_r/ Substitute _l for _r t Remove all leading pathname components, leaving the tail. & Repeat the previous substitution. g Apply the change globally, prefixing the above, e.g. `g&'. p Print the new command line but do not execute it. q Quote the substituted words, preventing further substitutions. x Like q, but break into words at blanks, tabs and newlines. Unless preceded by a `g' the modification is applied only to the first modifiable word. With substitutions, it is an error for no word to be applicable. The left hand side of substitutions are not regular expres- sions in the sense of the editors, but rather strings. Any Sprite v1.0 April 24, 1988 6 CSH User Commands CSH character may be used as the delimiter in place of `/'; a `\' quotes the delimiter into the _l and _r strings. The character `&' in the right hand side is replaced by the text from the left. A `\' quotes `&' also. A null _l uses the previous string either from a _l or from a contextual scan string _s in `!?_s?'. The trailing delimiter in the substitu- tion may be omitted if a newline follows immediately as may the trailing `?' in a contextual scan. A history reference may be given without an event specifica- tion, e.g. `!$'. In this case the reference is to the pre- vious command unless a previous history reference occurred on the same line in which case this form repeats the previ- ous reference. Thus `!?foo?^ !$' gives the first and last arguments from the command matching `?foo?'. A special abbreviation of a history reference occurs when the first non-blank character of an input line is a `^'. This is equivalent to `!:s^' providing a convenient short- hand for substitutions on the text of the previous line. Thus `^lb^lib' fixes the spelling of `lib' in the previous command. Finally, a history substitution may be surrounded with `{' and `}' if necessary to insulate it from the char- acters which follow. Thus, after `ls -ld ~paul' we might do `!{l}a' to do `ls -ld ~paula', while `!la' would look for a command starting `la'. QQuuoottaattiioonnss wwiitthh '' aanndd "" The quotation of strings by `'' and `"' can be used to prevent all or some of the remaining substitutions. Strings enclosed in `'' are prevented any further interpretation. Strings enclosed in `"' may be expanded as described below. In both cases the resulting text becomes (all or part of) a single word; only in one special case (see _C_o_m_m_a_n_d _S_u_b_s_t_i_t_i_- _t_i_o_n below) does a `"' quoted string yield parts of more than one word; `'' quoted strings never do. AAlliiaass ssuubbssttiittuuttiioonn The shell maintains a list of aliases which can be esta- blished, displayed and modified by the _a_l_i_a_s and _u_n_a_l_i_a_s commands. After a command line is scanned, it is parsed into distinct commands and the first word of each command, left-to-right, is checked to see if it has an alias. If it does, then the text which is the alias for that command is reread with the history mechanism available as though that command were the previous input line. The resulting words replace the command and argument list. If no reference is made to the history list, then the argument list is left unchanged. Sprite v1.0 April 24, 1988 7 CSH User Commands CSH Thus if the alias for `ls' is `ls -l' the command `ls /usr' would map to `ls -l /usr', the argument list here being undisturbed. Similarly if the alias for `lookup' was `grep !^ /etc/passwd' then `lookup bill' would map to `grep bill /etc/passwd'. If an alias is found, the word transformation of the input text is performed and the aliasing process begins again on the reformed input line. Looping is prevented if the first word of the new text is the same as the old by flagging it to prevent further aliasing. Other loops are detected and cause an error. Note that the mechanism allows aliases to introduce parser metasyntax. Thus we can `alias print 'pr \!* | lpr'' to make a command which _p_r'_s its arguments to the line printer. VVaarriiaabbllee ssuubbssttiittuuttiioonn The shell maintains a set of variables, each of which has as value a list of zero or more words. Some of these variables are set by the shell or referred to by it. For instance, the _a_r_g_v variable is an image of the shell's argument list, and words of this variable's value are referred to in spe- cial ways. The values of variables may be displayed and changed by using the _s_e_t and _u_n_s_e_t commands. Of the variables referred to by the shell a number are toggles; the shell does not care what their value is, only whether they are set or not. For instance, the _v_e_r_b_o_s_e variable is a toggle which causes command input to be echoed. The setting of this variable results from the --vv command line option. Other operations treat variables numerically. The `@' com- mand permits numeric calculations to be performed and the result assigned to a variable. Variable values are, how- ever, always represented as (zero or more) strings. For the purposes of numeric operations, the null string is con- sidered to be zero, and the second and subsequent words of multiword values are ignored. After the input line is aliased and parsed, and before each command is executed, variable substitution is performed keyed by `$' characters. This expansion can be prevented by preceding the `$' with a `\' except within `"'s where it aallwwaayyss occurs, and within `''s where it nneevveerr occurs. Strings quoted by ``' are interpreted later (see _C_o_m_m_a_n_d _s_u_b_s_t_i_t_u_t_i_o_n below) so `$' substitution does not occur there until later, if at all. A `$' is passed unchanged if fol- lowed by a blank, tab, or end-of-line. Sprite v1.0 April 24, 1988 8 CSH User Commands CSH Input/output redirections are recognized before variable expansion, and are variable expanded separately. Otherwise, the command name and entire argument list are expanded together. It is thus possible for the first (command) word to this point to generate more than one word, the first of which becomes the command name, and the rest of which become arguments. Unless enclosed in `"' or given the `:q' modifier the results of variable substitution may eventually be command and filename substituted. Within `"', a variable whose value consists of multiple words expands to a (portion of) a single word, with the words of the variables value separated by blanks. When the `:q' modifier is applied to a substitu- tion the variable will expand to multiple words with each word separated by a blank and quoted to prevent later com- mand or filename substitution. The following metasequences are provided for introducing variable values into the shell input. Except as noted, it is an error to reference a variable which is not set. $name ${name} Are replaced by the words of the value of variable _n_a_m_e, each separated by a blank. Braces insulate _n_a_m_e from following characters which would otherwise be part of it. Shell variables have names consisting of up to 20 letters and digits starting with a letter. The underscore character is considered a letter. If _n_a_m_e is not a shell variable, but is set in the environment, then that value is returned (but :: modif- iers and the other forms given below are not available in this case). $name[selector] ${name[selector]} May be used to select only some of the words from the value of _n_a_m_e. The selector is subjected to `$' substi- tution and may consist of a single number or two numbers separated by a `-'. The first word of a vari- ables value is numbered `1'. If the first number of a range is omitted it defaults to `1'. If the last member of a range is omitted it defaults to `$#name'. The selector `*' selects all words. It is not an error for a range to be empty if the second argument is omit- ted or in range. $#name ${#name} Gives the number of words in the variable. This is useful for later use in a `[selector]'. Sprite v1.0 April 24, 1988 9 CSH User Commands CSH $0 Substitutes the name of the file from which command input is being read. An error occurs if the name is not known. $number ${number} Equivalent to `$argv[number]'. $* Equivalent to `$argv[*]'. The modifiers `:e', `:h', `:t', `:r', `:q' and `:x' may be applied to the substitutions above as may `:gh', `:gt' and `:gr'. If braces `{' '}' appear in the command form then the modifiers must appear within the braces. TThhee ccuurrrreenntt iimmpplleemmeennttaattiioonn aalllloowwss oonnllyy oonnee ``::'' mmooddiiffiieerr oonn eeaacchh ``$$'' eexxppaannssiioonn.. The following substitutions may not be modified with `:' modifiers. $?name ${?name} Substitutes the string `1' if name is set, `0' if it is not. $?0 Substitutes `1' if the current input filename is known, `0' if it is not. $$ Substitute the (decimal) process number of the (parent) shell. $< Substitutes a line from the standard input, with no further interpretation thereafter. It can be used to read from the keyboard in a shell script. CCoommmmaanndd aanndd ffiilleennaammee ssuubbssttiittuuttiioonn The remaining substitutions, command and filename substitu- tion, are applied selectively to the arguments of builtin commands. This means that portions of expressions which are not evaluated are not subjected to these expansions. For commands which are not internal to the shell, the command name is substituted separately from the argument list. This occurs very late, after input-output redirection is per- formed, and in a child of the main shell. Sprite v1.0 April 24, 1988 10 CSH User Commands CSH CCoommmmaanndd ssuubbssttiittuuttiioonn Command substitution is indicated by a command enclosed in ``'. The output from such a command is normally broken into separate words at blanks, tabs and newlines, with null words being discarded, this text then replacing the original string. Within `"'s, only newlines force new words; blanks and tabs are preserved. In any case, the single final newline does not force a new word. Note that it is thus possible for a command substitu- tion to yield only part of a word, even if the command out- puts a complete line. FFiilleennaammee ssuubbssttiittuuttiioonn If a word contains any of the characters `*', `?', `[' or `{' or begins with the character `~', then that word is a candidate for filename substitution, also known as `glob- bing'. This word is then regarded as a pattern, and replaced with an alphabetically sorted list of file names which match the pattern. In a list of words specifying filename substitution it is an error for no pattern to match an existing file name, but it is not required for each pat- tern to match. Only the metacharacters `*', `?' and `[' imply pattern matching, the characters `~' and `{' being more akin to abbreviations. In matching filenames, the character `.' at the beginning of a filename or immediately following a `/', as well as the character `/' must be matched explicitly. The character `*' matches any string of characters, including the null string. The character `?' matches any single character. The sequence `[...]' matches any one of the characters enclosed. Within `[...]', a pair of characters separated by `-' matches any character lexically between the two. The character `~' at the beginning of a filename is used to refer to home directories. Standing alone, i.e. `~' it expands to the invokers home directory as reflected in the value of the variable _h_o_m_e. When followed by a name consist- ing of letters, digits and `-' characters the shell searches for a user with that name and substitutes their home direc- tory; thus `~ken' might expand to `/usr/ken' and `~ken/chmach' to `/usr/ken/chmach'. If the character `~' is followed by a character other than a letter or `/' or appears not at the beginning of a word, it is left undis- turbed. The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'. Left to right order is preserved, with results of matches being sorted separately at a low level to preserve Sprite v1.0 April 24, 1988 11 CSH User Commands CSH this order. This construct may be nested. Thus `~source/s1/{oldls,ls}.c' expands to `/usr/source/s1/oldls.c /usr/source/s1/ls.c' whether or not these files exist without any chance of error if the home directory for `source' is `/usr/source'. Similarly `../{memo,*box}' might expand to `../memo ../box ../mbox'. (Note that `memo' was not sorted with the results of matching `*box'.) As a spe- cial case `{', `}' and `{}' are passed undisturbed. IInnppuutt//oouuttppuutt The standard input and standard output of a command may be redirected with the following syntax: < name Open file _n_a_m_e (which is first variable, command and filename expanded) as the standard input. << word Read the shell input up to a line which is identical to _w_o_r_d. _W_o_r_d is not subjected to variable, filename or command substitution, and each input line is compared to _w_o_r_d before any substitutions are done on this input line. Unless a quoting `\', `"', `'' or ``' appears in _w_o_r_d variable and command substitution is performed on the intervening lines, allowing `\' to quote `$', `\' and ``'. Commands which are substituted have all blanks, tabs, and newlines preserved, except for the final newline which is dropped. The resultant text is placed in an anonymous temporary file which is given to the command as standard input. > name >! name >& name >&! name The file _n_a_m_e is used as standard output. If the file does not exist then it is created; if the file exists, its is truncated, its previous contents being lost. If the variable _n_o_c_l_o_b_b_e_r is set, then the file must not exist or be a character special file (e.g. a termi- nal or `/dev/null') or an error results. This helps prevent accidental destruction of files. In this case the `!' forms can be used and suppress this check. The forms involving `&' route the diagnostic output into the specified file as well as the standard output. _N_a_m_e is expanded in the same way as `<' input filenames are. >> name Sprite v1.0 April 24, 1988 12 CSH User Commands CSH >>& name >>! name >>&! name Uses file _n_a_m_e as standard output like `>' but places output at the end of the file. If the variable _n_o_c_l_o_b_b_e_r is set, then it is an error for the file not to exist unless one of the `!' forms is given. Other- wise similar to `>'. A command receives the environment in which the shell was invoked as modified by the input-output parameters and the presence of the command in a pipeline. Thus, unlike some previous shells, commands run from a file of shell commands have no access to the text of the commands by default; rather they receive the original standard input of the shell. The `<<' mechanism should be used to present inline data. This permits shell command scripts to function as components of pipelines and allows the shell to block read its input. Note that the default standard input for a com- mand run detached is nnoott modified to be the empty file `/dev/null'; rather the standard input remains as the origi- nal standard input of the shell. If this is a terminal and if the process attempts to read from the terminal, then the process will block and the user will be notified (see JJoobbss above). Diagnostic output may be directed through a pipe with the standard output. Simply use the form `|&' rather than just `|'. EExxpprreessssiioonnss A number of the builtin commands (to be described subse- quently) take expressions, in which the operators are simi- lar to those of C, with the same precedence. These expres- sions appear in the @, _e_x_i_t, _i_f, and _w_h_i_l_e commands. The following operators are available: || && | ^ & == != =~ !~ <= >= < > << >> + - * / % ! ~ ( ) Here the precedence increases to the right, `==' `!=' `=~' and `!~', `<=' `>=' `<' and `>', `<<' and `>>', `+' and `-', `*' `/' and `%' being, in groups, at the same level. The `==' `!=' `=~' and `!~' operators compare their arguments as strings; all others operate on numbers. The operators `=~' and `!~' are like `!=' and `==' except that the right hand side is a _p_a_t_t_e_r_n (containing, e.g. `*'s, `?'s and instances of `[...]') against which the left hand operand is matched. This reduces the need for use of the _s_w_i_t_c_h statement in shell scripts when all that is really needed is pattern matching. Sprite v1.0 April 24, 1988 13 CSH User Commands CSH Strings which begin with `0' are considered octal numbers. Null or missing arguments are considered `0'. The result of all expressions are strings, which represent decimal numbers. It is important to note that no two components of an expression can appear in the same word; except when adja- cent to components of expressions which are syntactically significant to the parser (`&' `|' `<' `>' `(' `)') they should be surrounded by spaces. Also available in expressions as primitive operands are com- mand executions enclosed in `{' and `}' and file enquiries of the form `-_l name' where _l is one of: r read access w write access x execute access e existence o ownership z zero size f plain file d directory The specified name is command and filename expanded and then tested to see if it has the specified relationship to the real user. If the file does not exist or is inaccessible then all enquiries return false, i.e. `0'. Command execu- tions succeed, returning true, i.e. `1', if the command exits with status 0, otherwise they fail, returning false, i.e. `0'. If more detailed status information is required then the command should be executed outside of an expression and the variable _s_t_a_t_u_s examined. CCoonnttrrooll ffllooww The shell contains a number of commands which can be used to regulate the flow of control in command files (shell scripts) and (in limited but useful ways) from terminal input. These commands all operate by forcing the shell to reread or skip in its input and, due to the implementation, restrict the placement of some of the commands. The _f_o_r_e_a_c_h, _s_w_i_t_c_h, and _w_h_i_l_e statements, as well as the _i_f-_t_h_e_n-_e_l_s_e form of the _i_f statement require that the major keywords appear in a single simple command on an input line as shown below. If the shell's input is not seekable, the shell buffers up input whenever a loop is being read and performs seeks in this internal buffer to accomplish the rereading implied by the loop. (To the extent that this allows, backward goto's will succeed on non-seekable inputs.) Sprite v1.0 April 24, 1988 14 CSH User Commands CSH BBuuiillttiinn ccoommmmaannddss Builtin commands are executed within the shell. If a buil- tin command occurs as any component of a pipeline except the last then it is executed in a subshell. aalliiaass aalliiaass name aalliiaass name wordlist The first form prints all aliases. The second form prints the alias for name. The final form assigns the specified _w_o_r_d_l_i_s_t as the alias of _n_a_m_e; _w_o_r_d_l_i_s_t is command and filename substituted. _N_a_m_e is not allowed to be _a_l_i_a_s or _u_n_a_l_i_a_s. aalllloocc Shows the amount of dynamic memory acquired, broken down into used and free memory. With an argument shows the number of free and used blocks in each size category. The categories start at size 8 and double at each step. This command's output may vary across sys- tem types, since systems other than the VAX may use a different memory allocator. bbgg bbgg %%job ... Puts the current or specified jobs into the background, continuing them if they were stopped. bbrreeaakk Causes execution to resume after the _e_n_d of the nearest enclosing _f_o_r_e_a_c_h or _w_h_i_l_e. The remaining commands on the current line are executed. Multi-level breaks are thus possible by writing them all on one line. bbrreeaakkssww Causes a break from a _s_w_i_t_c_h, resuming after the _e_n_d_s_w. ccaassee label: A label in a _s_w_i_t_c_h statement as discussed below. ccdd ccdd name cchhddiirr cchhddiirr name Change the shell's working directory to directory _n_a_m_e. If no argument is given then change to the home direc- tory of the user. If _n_a_m_e is not found as a subdirectory of the current directory (and does not begin with `/', `./' or `../'), then each component of the variable _c_d_p_a_t_h is checked to see if it has a subdirectory _n_a_m_e. Finally, if all Sprite v1.0 April 24, 1988 15 CSH User Commands CSH else fails but _n_a_m_e is a shell variable whose value begins with `/', then this is tried to see if it is a directory. ccoonnttiinnuuee Continue execution of the nearest enclosing _w_h_i_l_e or _f_o_r_e_a_c_h. The rest of the commands on the current line are executed. ddeeffaauulltt:: Labels the default case in a _s_w_i_t_c_h statement. The default should come after all _c_a_s_e labels. ddiirrss Prints the directory stack; the top of the stack is at the left, the first directory in the stack being the current directory. eecchhoo wordlist eecchhoo --nn wordlist The specified words are written to the shells standard output, separated by spaces, and terminated with a new- line unless the --nn option is specified. eellssee eenndd eennddiiff eennddssww See the description of the _f_o_r_e_a_c_h, _i_f, _s_w_i_t_c_h, and _w_h_i_l_e statements below. eevvaall arg ... (As in _s_h(1).) The arguments are read as input to the shell and the resulting command(s) executed in the con- text of the current shell. This is usually used to execute commands generated as the result of command or variable substitution, since parsing occurs before these substitutions. See _t_s_e_t(1) for an example of using _e_v_a_l. eexxeecc command The specified command is executed in place of the current shell. eexxiitt eexxiitt(expr) The shell exits either with the value of the _s_t_a_t_u_s variable (first form) or with the value of the speci- fied _e_x_p_r (second form). ffgg ffgg %%job ... Sprite v1.0 April 24, 1988 16 CSH User Commands CSH Brings the current or specified jobs into the fore- ground, continuing them if they were stopped. ffoorreeaacchh name (wordlist) ... eenndd The variable _n_a_m_e is successively set to each member of _w_o_r_d_l_i_s_t and the sequence of commands between this com- mand and the matching _e_n_d are executed. (Both _f_o_r_e_a_c_h and _e_n_d must appear alone on separate lines.) The builtin command _c_o_n_t_i_n_u_e may be used to continue the loop prematurely and the builtin command _b_r_e_a_k to terminate it prematurely. When this command is read from the terminal, the loop is read up once prompting with `?' before any statements in the loop are exe- cuted. If you make a mistake typing in a loop at the terminal you can rub it out. gglloobb wordlist Like _e_c_h_o but no `\' escapes are recognized and words are delimited by null characters in the output. Useful for programs which wish to use the shell to filename expand a list of words. ggoottoo word The specified _w_o_r_d is filename and command expanded to yield a string of the form `label'. The shell rewinds its input as much as possible and searches for a line of the form `label:' possibly preceded by blanks or tabs. Execution continues after the specified line. hhaasshhssttaatt Print a statistics line indicating how effective the internal hash table has been at locating commands (and avoiding _e_x_e_c's). An _e_x_e_c is attempted for each com- ponent of the _p_a_t_h where the hash function indicates a possible hit, and in each component which does not begin with a `/'. hhiissttoorryy hhiissttoorryy _n hhiissttoorryy --rr _n hhiissttoorryy --hh _n Displays the history event list; if _n is given only the _n most recent events are printed. The --rr option rev- erses the order of printout to be most recent first rather than oldest first. The --hh option causes the history list to be printed without leading numbers. This is used to produce files suitable for sourceing using the -h option to _s_o_u_r_c_e. Sprite v1.0 April 24, 1988 17 CSH User Commands CSH iiff (expr) command If the specified expression evaluates true, then the single _c_o_m_m_a_n_d with arguments is executed. Variable substitution on _c_o_m_m_a_n_d happens early, at the same time it does for the rest of the _i_f command. _C_o_m_m_a_n_d must be a simple command, not a pipeline, a command list, or a parenthesized command list. Input/output redirection occurs even if _e_x_p_r is false, when command is nnoott exe- cuted (this is a bug). iiff (expr) tthheenn ... eellssee iiff (expr2) tthheenn ... eellssee ... eennddiiff If the specified _e_x_p_r is true then the commands to the first _e_l_s_e are executed; otherwise if _e_x_p_r_2 is true then the commands to the second _e_l_s_e are executed, etc. Any number of _e_l_s_e-_i_f pairs are possible; only one _e_n_d_i_f is needed. The _e_l_s_e part is likewise optional. (The words _e_l_s_e and _e_n_d_i_f must appear at the beginning of input lines; the _i_f must appear alone on its input line or after an _e_l_s_e.) jjoobbss jjoobbss --ll Lists the active jobs; given the --ll options lists pro- cess id's in addition to the normal information. kkiillll %%job kkiillll --sig %%job ... kkiillll pid kkiillll --sig pid ... kkiillll --ll Sends either the TERM (terminate) signal or the speci- fied signal to the specified jobs or processes. Sig- nals are either given by number or by names (as given in /_u_s_r/_i_n_c_l_u_d_e/_s_i_g_n_a_l._h, stripped of the prefix ``SIG''). The signal names are listed by ``kill -l''. There is no default, saying just `kill' does not send a signal to the current job. If the signal being sent is TERM (terminate) or HUP (hangup), then the job or pro- cess will be sent a CONT (continue) signal as well. lliimmiitt lliimmiitt _r_e_s_o_u_r_c_e lliimmiitt _r_e_s_o_u_r_c_e _m_a_x_i_m_u_m-_u_s_e lliimmiitt --hh lliimmiitt --hh _r_e_s_o_u_r_c_e lliimmiitt --hh _r_e_s_o_u_r_c_e _m_a_x_i_m_u_m-_u_s_e Sprite v1.0 April 24, 1988 18 CSH User Commands CSH Limits the consumption by the current process and each process it creates to not individually exceed _m_a_x_i_m_u_m- _u_s_e on the specified _r_e_s_o_u_r_c_e. If no _m_a_x_i_m_u_m-_u_s_e is given, then the current limit is printed; if no _r_e_s_o_u_r_c_e is given, then all limitations are given. If the --hh flag is given, the hard limits are used instead of the current limits. The hard limits impose a ceil- ing on the values of the current limits. Only the super-user may raise the hard limits, but a user may lower or raise the current limits within the legal range. Resources controllable currently include _c_p_u_t_i_m_e (the maximum number of cpu-seconds to be used by each pro- cess), _f_i_l_e_s_i_z_e (the largest single file which can be created), _d_a_t_a_s_i_z_e (the maximum growth of the data+stack region via _s_b_r_k(2) beyond the end of the program text), _s_t_a_c_k_s_i_z_e (the maximum size of the automatically-extended stack region), and _c_o_r_e_d_u_m_p_s_i_z_e (the size of the largest core dump that will be created). The _m_a_x_i_m_u_m-_u_s_e may be given as a (floating point or integer) number followed by a scale factor. For all limits other than _c_p_u_t_i_m_e the default scale is `k' or `kilobytes' (1024 bytes); a scale factor of `m' or `megabytes' may also be used. For _c_p_u_t_i_m_e the default scaling is `seconds', while `m' for minutes or `h' for hours, or a time of the form `mm:ss' giving minutes and seconds may be used. For both _r_e_s_o_u_r_c_e names and scale factors, unambiguous prefixes of the names suffice. llooggiinn Terminate a login shell, replacing it with an instance of //bbiinn//llooggiinn.. This is one way to log off, included for compatibility with _s_h(1). llooggoouutt Terminate a login shell. Especially useful if _i_g_n_o_r_e_e_o_f is set. nniiccee nniiccee +number nniiccee command nniiccee +number command The first form sets the scheduling priority for this shell to 4. The second form sets the priority to the given number. The final two forms run command at priority 4 and _n_u_m_b_e_r respectively. The greater the number, the less cpu the process will get. The super- Sprite v1.0 April 24, 1988 19 CSH User Commands CSH user may specify negative priority by using `nice -number ...'. Command is always executed in a sub- shell, and the restrictions placed on commands in sim- ple _i_f statements apply. nnoohhuupp nnoohhuupp command The first form can be used in shell scripts to cause hangups to be ignored for the remainder of the script. The second form causes the specified command to be run with hangups ignored. All processes detached with `&' are effectively _n_o_h_u_p'_e_d. nnoottiiffyy nnoottiiffyy %%job ... Causes the shell to notify the user asynchronously when the status of the current or specified jobs changes; normally notification is presented before a prompt. This is automatic if the shell variable _n_o_t_i_f_y is set. oonniinnttrr oonniinnttrr - oonniinnttrr label Control the action of the shell on interrupts. The first form restores the default action of the shell on interrupts which is to terminate shell scripts or to return to the terminal command input level. The second form `onintr -' causes all interrupts to be ignored. The final form causes the shell to execute a `goto label' when an interrupt is received or a child process terminates because it was interrupted. In any case, if the shell is running detached and interrupts are being ignored, all forms of _o_n_i_n_t_r have no meaning and interrupts continue to be ignored by the shell and all invoked commands. ppooppdd ppooppdd +n Pops the directory stack, returning to the new top directory. With an argument `+_n' discards the _nth entry in the stack. The elements of the directory stack are numbered from 0 starting at the top. ppuusshhdd ppuusshhdd name ppuusshhdd +n With no arguments, _p_u_s_h_d exchanges the top two elements of the directory stack. Given a _n_a_m_e argument, _p_u_s_h_d changes to the new directory (ala _c_d) and pushes the old current working directory (as in _c_s_w) onto the directory stack. With a numeric argument, rotates the Sprite v1.0 April 24, 1988 20 CSH User Commands CSH _nth argument of the directory stack around to be the top element and changes to it. The members of the directory stack are numbered from the top starting at 0. rreehhaasshh Causes the internal hash table of the contents of the directories in the _p_a_t_h variable to be recomputed. This is needed if new commands are added to directories in the _p_a_t_h while you are logged in. This should only be necessary if you add commands to one of your own directories, or if a systems programmer changes the contents of one of the system directories. rreeppeeaatt count command The specified _c_o_m_m_a_n_d which is subject to the same res- trictions as the _c_o_m_m_a_n_d in the one line _i_f statement above, is executed _c_o_u_n_t times. I/O redirections occur exactly once, even if _c_o_u_n_t is 0. sseett sseett name sseett name=word sseett name[index]=word sseett name=(wordlist) The first form of the command shows the value of all shell variables. Variables which have other than a single word as value print as a parenthesized word list. The second form sets _n_a_m_e to the null string. The third form sets _n_a_m_e to the single _w_o_r_d. The fourth form sets the _i_n_d_e_x'_t_h component of name to word; this component must already exist. The final form sets _n_a_m_e to the list of words in _w_o_r_d_l_i_s_t. In all cases the value is command and filename expanded. These arguments may be repeated to set multiple values in a single set command. Note however, that variable expansion happens for all arguments before any setting occurs. sseetteennvv sseetteennvv name value sseetteennvv name The first form lists all current environment variables. The last form sets the value of environment variable _n_a_m_e to be _v_a_l_u_e, a single string. The second form sets _n_a_m_e to an empty string. The most commonly used environment variable USER, TERM, and PATH are automati- cally imported to and exported from the _c_s_h variables _u_s_e_r, _t_e_r_m, and _p_a_t_h; there is no need to use _s_e_t_e_n_v for these. Sprite v1.0 April 24, 1988 21 CSH User Commands CSH sshhiifftt sshhiifftt variable The members of _a_r_g_v are shifted to the left, discarding _a_r_g_v[_1]. It is an error for _a_r_g_v not to be set or to have less than one word as value. The second form per- forms the same function on the specified variable. ssoouurrccee name ssoouurrccee --hh name The shell reads commands from _n_a_m_e. _S_o_u_r_c_e commands may be nested; if they are nested too deeply the shell may run out of file descriptors. An error in a _s_o_u_r_c_e at any level terminates all nested _s_o_u_r_c_e commands. Nor- mally input during _s_o_u_r_c_e commands is not placed on the history list; the -h option causes the commands to be placed in the history list without being executed. ssttoopp ssttoopp %%job ... Stops the current or specified job which is executing in the background. ssuussppeenndd Causes the shell to stop in its tracks, much as if it had been sent a stop signal with ^^ZZ. This is most often used to stop shells started by _s_u(1). sswwiittcchh (string) ccaassee str1: ... bbrreeaakkssww ... ddeeffaauulltt:: ... bbrreeaakkssww eennddssww Each case label is successively matched, against the specified _s_t_r_i_n_g which is first command and filename expanded. The file metacharacters `*', `?' and `[...]' may be used in the case labels, which are variable expanded. If none of the labels match before a `default' label is found, then the execution begins after the default label. Each case label and the default label must appear at the beginning of a line. The command _b_r_e_a_k_s_w causes execution to continue after the _e_n_d_s_w. Otherwise control may fall through case labels and default labels as in C. If no label matches and there is no default, execution continues after the _e_n_d_s_w. ttiimmee ttiimmee command Sprite v1.0 April 24, 1988 22 CSH User Commands CSH With no argument, a summary of time used by this shell and its children is printed. If arguments are given the specified simple command is timed and a time sum- mary as described under the _t_i_m_e variable is printed. If necessary, an extra shell is created to print the time statistic when the command completes. uummaasskk uummaasskk value The file creation mask is displayed (first form) or set to the specified value (second form). The mask is given in octal. Common values for the mask are 002 giving all access to the group and read and execute access to others or 022 giving all access except no write access for users in the group or others. uunnaalliiaass pattern All aliases whose names match the specified pattern are discarded. Thus all aliases are removed by `unalias *'. It is not an error for nothing to be _u_n_a_l_i_a_s_e_d. uunnhhaasshh Use of the internal hash table to speed location of executed programs is disabled. uunnlliimmiitt uunnlliimmiitt _r_e_s_o_u_r_c_e uunnlliimmiitt --hh uunnlliimmiitt --hh _r_e_s_o_u_r_c_e Removes the limitation on _r_e_s_o_u_r_c_e. If no _r_e_s_o_u_r_c_e is specified, then all _r_e_s_o_u_r_c_e limitations are removed. If --hh is given, the corresponding hard limits are removed. Only the super-user may do this. uunnsseett pattern All variables whose names match the specified pattern are removed. Thus all variables are removed by `unset *'; this has noticeably distasteful side-effects. It is not an error for nothing to be _u_n_s_e_t. uunnsseetteennvv pattern Removes all variables whose name match the specified pattern from the environment. See also the _s_e_t_e_n_v com- mand above and _p_r_i_n_t_e_n_v(1). wwaaiitt All background jobs are waited for. It the shell is interactive, then an interrupt can disrupt the wait, at which time the shell prints names and job numbers of all jobs known to be outstanding. wwhhiillee (expr) Sprite v1.0 April 24, 1988 23 CSH User Commands CSH ... eenndd While the specified expression evaluates non-zero, the commands between the _w_h_i_l_e and the matching end are evaluated. _B_r_e_a_k and _c_o_n_t_i_n_u_e may be used to terminate or continue the loop prematurely. (The _w_h_i_l_e and _e_n_d must appear alone on their input lines.) Prompting occurs here the first time through the loop as for the _f_o_r_e_a_c_h statement if the input is a terminal. %%job Brings the specified job into the foreground. %%job && Continues the specified job in the background. @@ @@ name = expr @@ name[index] = expr The first form prints the values of all the shell vari- ables. The second form sets the specified _n_a_m_e to the value of _e_x_p_r. If the expression contains `<', `>', `&' or `|' then at least this part of the expression must be placed within `(' `)'. The third form assigns the value of _e_x_p_r to the _i_n_d_e_x'_t_h argument of _n_a_m_e. Both _n_a_m_e and its _i_n_d_e_x'_t_h component must already exist. The operators `*=', `+=', etc are available as in C. The space separating the name from the assignment operator is optional. Spaces are, however, mandatory in separating components of _e_x_p_r which would otherwise be single words. Special postfix `++' and `--' operators increment and decrement _n_a_m_e respectively, i.e. `@ i++'. PPrree--ddeeffiinneedd aanndd eennvviirroonnmmeenntt vvaarriiaabblleess The following variables have special meaning to the shell. Of these, _a_r_g_v, _c_w_d, _h_o_m_e, _p_a_t_h, _p_r_o_m_p_t, _s_h_e_l_l and _s_t_a_t_u_s are always set by the shell. Except for _c_w_d and _s_t_a_t_u_s this setting occurs only at initialization; these variables will not then be modified unless this is done explicitly by the user. This shell copies the environment variable USER into the variable _u_s_e_r, TERM into _t_e_r_m, and HOME into _h_o_m_e, and copies these back into the environment whenever the normal shell variables are reset. The environment variable PATH is likewise handled; it is not necessary to worry about its setting other than in the file ._c_s_h_r_c as inferior _c_s_h processes will import the definition of _p_a_t_h from the Sprite v1.0 April 24, 1988 24 CSH User Commands CSH environment, and re-export it if you then change it. aarrggvv Set to the arguments to the shell, it is from this variable that positional parameters are substituted, i.e. `$1' is replaced by `$argv[1]', etc. ccddppaatthh Gives a list of alternate directories searched to find subdirectories in _c_h_d_i_r com- mands. ccwwdd The full pathname of the current directory. eecchhoo Set when the --xx command line option is given. Causes each command and its arguments to be echoed just before it is executed. For non- builtin commands all expansions occur before echoing. Builtin commands are echoed before command and filename substitution, since these substitutions are then done selec- tively. ffiilleecc Enable file name completion. hhiissttcchhaarrss Can be given a string value to change the characters used in history substitution. The first character of its value is used as the history substitution character, replacing the default character !. The second character of its value replaces the character |^ in quick substitutions. hhiissttoorryy Can be given a numeric value to control the size of the history list. Any command which has been referenced in this many events will not be discarded. Too large values of _h_i_s_- _t_o_r_y may run the shell out of memory. The last executed command is always saved on the history list. hhoommee The home directory of the invoker, initial- ized from the environment. The filename expansion of `~~' refers to this variable. iiggnnoorreeeeooff If set the shell ignores end-of-file from input devices which are terminals. This prevents shells from accidentally being killed by control-D's. mmaaiill The files where the shell checks for mail. This is done after each command completion which will result in a prompt, if a specified Sprite v1.0 April 24, 1988 25 CSH User Commands CSH interval has elapsed. The shell says `You have new mail.' if the file exists with an access time not greater than its modify time. If the first word of the value of _m_a_i_l is numeric it specifies a different mail check- ing interval, in seconds, than the default, which is 10 minutes. If multiple mail files are specified, then the shell says `New mail in _n_a_m_e' when there is mail in the file _n_a_m_e. nnoocclloobbbbeerr As described in the section on _I_n_p_u_t/_o_u_t_p_u_t, restrictions are placed on output redirection to insure that files are not accidentally destroyed, and that `>>' redirections refer to existing files. nnoogglloobb If set, filename expansion is inhibited. This is most useful in shell scripts which are not dealing with filenames, or after a list of filenames has been obtained and further expansions are not desirable. nnoonnoommaattcchh If set, it is not an error for a filename expansion to not match any existing files; rather the primitive pattern is returned. It is still an error for the primitive pattern to be malformed, i.e. `echo [' still gives an error. nnoottiiffyy If set, the shell notifies asynchronously of job completions. The default is to rather present job completions just before printing a prompt. ppaatthh Each word of the path variable specifies a directory in which commands are to be sought for execution. A null word specifies the current directory. If there is no _p_a_t_h vari- able then only full path names will execute. The usual search path is `.', `/bin' and `/usr/bin', but this may vary from system to system. For the super-user the default search path is `/etc', `/bin' and `/usr/bin'. A shell which is given neither the --cc nor the --tt option will normally hash the contents of the directories in the _p_a_t_h variable after reading ._c_s_h_r_c, and each time the _p_a_t_h vari- able is reset. If new commands are added to these directories while the shell is active, Sprite v1.0 April 24, 1988 26 CSH User Commands CSH it may be necessary to give the _r_e_h_a_s_h or the commands may not be found. pprroommpptt The string which is printed before each com- mand is read from an interactive terminal input. If a `!' appears in the string it will be replaced by the current event number unless a preceding `\' is given. Default is `% ', or `# ' for the super-user. ssaavveehhiisstt is given a numeric value to control the number of entries of the history list that are saved in ~/.history when the user logs out. Any command which has been referenced in this many events will be saved. During start up the shell sources ~/.history into the history list enabling history to be saved across logins. Too large values of _s_a_v_e_h_i_s_t will slow down the shell during start up. sshheellll The file in which the shell resides. This is used in forking shells to interpret files which have execute bits set, but which are not executable by the system. (See the description of _N_o_n-_b_u_i_l_t_i_n _C_o_m_m_a_n_d _E_x_e_c_u_t_i_o_n below.) Initialized to the (system-dependent) home of the shell. ssttaattuuss The status returned by the last command. If it terminated abnormally, then 0200 is added to the status. Builtin commands which fail return exit status `1', all other builtin commands set status `0'. ttiimmee Controls automatic timing of commands. If set, then any command which takes more than this many cpu seconds will cause a line giv- ing user, system, and real times and a utili- zation percentage which is the ratio of user plus system times to real time to be printed when it terminates. vveerrbboossee Set by the --vv command line option, causes the words of each command to be printed after history substitution. NNoonn--bbuuiillttiinn ccoommmmaanndd eexxeeccuuttiioonn When a command to be executed is found to not be a builtin command the shell attempts to execute the command via _e_x_e_c_v_e(2). Each word in the variable _p_a_t_h names a directory from which the shell will attempt to execute the command. Sprite v1.0 April 24, 1988 27 CSH User Commands CSH If it is given neither a --cc nor a --tt option, the shell will hash the names in these directories into an internal table so that it will only try an _e_x_e_c in a directory if there is a possibility that the command resides there. This greatly speeds command location when a large number of directories are present in the search path. If this mechanism has been turned off (via _u_n_h_a_s_h), or if the shell was given a --cc or --tt argument, and in any case for each directory component of _p_a_t_h which does not begin with a `/', the shell concatenates with the given command name to form a path name of a file which it then attempts to execute. Parenthesized commands are always executed in a subshell. Thus `(cd ; pwd) ; pwd' prints the _h_o_m_e directory; leaving you where you were (printing this after the home directory), while `cd ; pwd' leaves you in the _h_o_m_e directory. Parenthesized commands are most often used to prevent _c_h_d_i_r from affecting the current shell. If the file has execute permissions but is not an executable binary to the system, then it is assumed to be a file con- taining shell commands and a new shell is spawned to read it. If there is an _a_l_i_a_s for _s_h_e_l_l then the words of the alias will be prepended to the argument list to form the shell command. The first word of the _a_l_i_a_s should be the full path name of the shell (e.g. `$shell'). Note that this is a special, late occurring, case of _a_l_i_a_s substitution, and only allows words to be prepended to the argument list without modification. AArrgguummeenntt lliisstt pprroocceessssiinngg If argument 0 to the shell is `-' then this is a login shell. The flag arguments are interpreted as follows: --bb This flag forces a ``break'' from option processing, causing any further shell arguments to be treated as non-option arguments. The remaining arguments will not be interpreted as shell options. This may be used to pass options to a shell script without confusion or possible subterfuge. The shell will not run a set-user ID script without this option. --cc Commands are read from the (single) following argument which must be present. Any remaining arguments are placed in _a_r_g_v. --ee The shell exits if any invoked command terminates abnormally or yields a non-zero exit status. Sprite v1.0 April 24, 1988 28 CSH User Commands CSH --ff The shell will start faster, because it will neither search for nor execute commands from the file `.cshrc' in the invoker's home directory. --ii The shell is interactive and prompts for its top-level input, even if it appears to not be a terminal. Shells are interactive without this option if their inputs and outputs are terminals. --nn Commands are parsed, but not executed. This aids in syntactic checking of shell scripts. --ss Command input is taken from the standard input. --tt A single line of input is read and executed. A `\' may be used to escape the newline at the end of this line and continue onto another line. --vv Causes the _v_e_r_b_o_s_e variable to be set, with the effect that command input is echoed after history substitu- tion. --xx Causes the _e_c_h_o variable to be set, so that commands are echoed immediately before execution. --VV Causes the _v_e_r_b_o_s_e variable to be set even before `.cshrc' is executed. --XX Is to --xx as --VV is to --vv.. After processing of flag arguments, if arguments remain but none of the --cc,, --ii,, --ss,, or --tt options was given, the first argument is taken as the name of a file of commands to be executed. The shell opens this file, and saves its name for possible resubstitution by `$0'. Since many systems use either the standard version 6 or version 7 shells whose shell scripts are not compatible with this shell, the shell will execute such a `standard' shell if the first character of a script is not a `#', i.e. if the script does not start with a comment. Remaining arguments initialize the variable _a_r_g_v. SSiiggnnaall hhaannddlliinngg The shell normally ignores _q_u_i_t signals. Jobs running detached (either by `&' or the _b_g or %%...... && commands) are immune to signals generated from the keyboard, including hangups. Other signals have the values which the shell inherited from its parent. The shells handling of inter- rupts and terminate signals in shell scripts can be con- trolled by _o_n_i_n_t_r. Login shells catch the _t_e_r_m_i_n_a_t_e signal; otherwise this signal is passed on to children from the Sprite v1.0 April 24, 1988 29 CSH User Commands CSH state in the shell's parent. In no case are interrupts allowed when a login shell is reading the file `.logout'. AAUUTTHHOORR William Joy. Job control and directory stack features first implemented by J.E. Kulp of I.I.A.S.A, Laxenburg, Austria, with different syntax than that used now. File name comple- tion code written by Ken Greer, HP Labs. FFIILLEESS ~/.cshrc Read at beginning of execution by each shell. ~/.login Read by login shell, after `.cshrc' at login. ~/.logout Read by login shell, at logout. /bin/sh Standard shell, for shell scripts not starting with a `#'. /tmp/sh* Temporary file for `<<'. /etc/passwd Source of home directories for `~name'. LLIIMMIITTAATTIIOONNSS Words can be no longer than 1024 characters. The system limits argument lists to 10240 characters. The number of arguments to a command which involves filename expansion is limited to 1/6'th the number of characters allowed in an argument list. Command substitutions may substitute no more characters than are allowed in an argument list. To detect looping, the shell restricts the number of _a_l_i_a_s substitu- tions on a single line to 20. SSEEEE AALLSSOO sh(1), access(2), execve(2), fork(2), killpg(2), pipe(2), sigvec(2), umask(2), setrlimit(2), wait(2), tty(4), a.out(5), environ(7), `An introduction to the C shell' BBUUGGSS When a command is restarted from a stop, the shell prints the directory it started in if this is different from the current directory; this can be misleading (i.e. wrong) as the job may have changed directories internally. Shell builtin functions are not stoppable/restartable. Com- mand sequences of the form `a ; b ; c' are also not handled gracefully when stopping is attempted. If you suspend `b', the shell will then immediately execute `c'. This is espe- cially noticeable if this expansion results from an _a_l_i_a_s. It suffices to place the sequence of commands in ()'s to force it to a subshell, i.e. `( a ; b ; c )'. Control over tty output after processes are started is prim- itive; perhaps this will inspire someone to work on a good virtual terminal interface. In a virtual terminal interface much more interesting things could be done with output con- trol. Sprite v1.0 April 24, 1988 30 CSH User Commands CSH Alias substitution is most often used to clumsily simulate shell procedures; shell procedures should be provided rather than aliases. Commands within loops, prompted for by `?', are not placed in the _h_i_s_t_o_r_y list. Control structure should be parsed rather than being recognized as built-in commands. This would allow control commands to be placed anywhere, to be combined with `|', and to be used with `&' and `;' metasyn- tax. It should be possible to use the `:' modifiers on the output of command substitutions. All and more than one `:' modif- ier should be allowed on `$' substitutions. The way the ffiilleecc facility is implemented is ugly and expen- sive. Sprite v1.0 April 24, 1988 31