OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) NAME oldcsh - a shell (command interpreter) with C-like syntax SYNOPSIS oldcsh [ -cefinstvVxX ] [ arg ... ] DESCRIPTION _O_l_d_c_s_h is a command language interpreter similar to _c_s_h(1) but without its process control facilities. It begins by executing commands from the file `.cshrc' in the _h_o_m_e direc- tory of the invoker. If this is a login shell then it also executes commands from the file `.login' there. In the nor- mal case, the shell will then begin reading commands from the terminal, prompting with `% '. Processing of arguments and the use of the shell to process files containing 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. Lexical structure 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 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 `"'. Commands Printed 7/25/83 1 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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 waiting for it to terminate by following it with an `&'. Such a sequence is automatically prevented from being ter- minated by a hangup signal; the _n_o_h_u_p command need not be used. 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.) Substitutions We now describe the various transformations the shell per- forms on the input in the order in which they occur. History substitutions History substitutions can be used to reintroduce sequences of words from previous commands, possibly performing modifi- cations on these words. Thus history substitutions provide a generalization of a _r_e_d_o function. History substitutions begin with the character `!' and may begin anywhere in the input stream if a history substitution is not already in progress. This `!' may be preceded by an `\' to prevent its special meaning; a `!' is passed unchanged when it is followed by a blank, tab, newline, `=' 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 size of which is controlled by the _h_i_s_t_o_r_y variable. The previous command is always retained. Commands are numbered sequentially from 1. For definiteness, consider the following output from the history command: Printed 7/25/83 2 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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 `!' 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 `!w' 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. The form `!#' references the current command (the one being typed in). It allows a word to be selected from further left in the line, to avoid retyping a long name, as in `!#:1'. To select words from an event we can follow the event specification by a `:' and a designator for the desired words. The words of a 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. 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&'. Printed 7/25/83 3 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) p Print the new command 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. In any case 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 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'. Quotations with ' and " 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 `"' are yet variable and command 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_u_- _t_i_o_n below) does a `"' quoted string yield parts of more than one word; `' quoted strings never do. Alias substitution Printed 7/25/83 4 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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. 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. Variable substitution 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 -v 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 Printed 7/25/83 5 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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 always occurs, and within `'s where it never 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. 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 sin- gle word, with the words of the variables value separated by blanks. When the `:q' modifier is applied to a substitution the variable will expand to multiple words with each word separated by a blank and quoted to prevent later command 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, digits, and underscores. If _n_a_m_e is not a shell variable, but is set in the environ- ment, then that value is returned (but : modifiers 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 Printed 7/25/83 6 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) variables 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]'. $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 `: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 modif- iers must appear within the braces. The current implementa- tion allows only one `:' modifier on each `$' expansion. 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 know, `0' if it is not. $$ Substitute the (decimal) process number of the (parent) shell. Command and filename substitution 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 Printed 7/25/83 7 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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. Command substitution 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. Filename substitution 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 Printed 7/25/83 8 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) undisturbed. 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 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. Input/output 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 Printed 7/25/83 9 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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 >>& 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 `>'. If a command is run detached (followed by `&') then the default standard input for the command is the empty file `/dev/null'. Otherwise the 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 pipe- line. 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 stan- dard 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. Diagnostic output may be directed through a pipe with the standard output. Simply use the form `|&' rather than just `|'. Expressions 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 oth- ers operate on numbers. 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 adjacent to components of expressions Printed 7/25/83 10 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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. Control flow 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.) Builtin commands 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. Printed 7/25/83 11 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) alias alias name alias 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 alloc Shows the amount of dynamic core in use, broken down into used and free core, and address of the last loca- tion in the heap. With an argument shows each used and free block on the internal dynamic memory chain indi- cating its address, size, and whether it is used or free. This is a debugging command and may not work in production versions of the shell; it requires a modi- fied version of the system memory allocator. break 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. breaksw Causes a break from a _s_w_i_t_c_h, resuming after the _e_n_d_s_w. case label: A label in a _s_w_i_t_c_h statement as discussed below. cd cd name chdir chdir name Change the shells 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 direc- tory (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 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. continue 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. Printed 7/25/83 12 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) default: Labels the default case in a _s_w_i_t_c_h statement. The default should come after all _c_a_s_e labels. echo wordlist The specified words are written to the shells standard output. A `\c' causes the echo to complete without printing a newline, akin to the `\c' in _n_r_o_f_f(1). A `\n' in wordlist causes a newline to be printed. Oth- erwise the words are echoed, separated by spaces. else end endif endsw 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. exec command The specified command is executed in place of the current shell. exit exit(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). foreach name (wordlist) ... end 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. glob 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. goto word The specified _w_o_r_d is filename and command expanded to Printed 7/25/83 13 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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. hashstat 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 ``/''. history Displays the history event list. if (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 not exe- cuted (this is a bug). if (expr) then ... else if (expr2) then ... else ... endif If the specified _e_x_p_r is true then the commands to the first _e_l_s_e are executed; else if _e_x_p_r_2 is true then the commands to the second else 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.) login Terminate a login shell, replacing it with an instance of /bin/login. This is one way to log off, included for compatibility with /bin/sh. logout Terminate a login shell. Especially useful if _i_g_n_o_r_e_e_o_f is set. Printed 7/25/83 14 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) nice nice +number nice command nice +number command The first form sets the _n_i_c_e for this shell to 4. The second form sets the _n_i_c_e to the given number. The final two forms run command at priority 4 and _n_u_m_b_e_r respectively. The super-user may specify negative niceness by using `nice -number ...'. Command is always executed in a sub-shell, and the restrictions place on commands in simple _i_f statements apply. nohup nohup 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. On the Computer Center systems at UC Berkeley, this also _s_u_b_m_i_t_s the process. Unless the shell is running detached, _n_o_h_u_p has no effect. All processes detached with ``&'' are automatically _n_o_h_u_p'_e_d. (Thus, _n_o_h_u_p is not really needed.) onintr onintr - onintr 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. rehash 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. repeat 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 Printed 7/25/83 15 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) above, is executed _c_o_u_n_t times. I/O redirections occurs exactly once, even if _c_o_u_n_t is 0. set set name set name=word set name[index]=word set 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. setenv name value (Version 7 systems only.) Sets the value of environment variable _n_a_m_e to be _v_a_l_u_e, a single string. Useful environment variables are `TERM' the type of your ter- minal and `SHELL' the shell you are using. shift shift 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. source 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. Input during _s_o_u_r_c_e commands is never placed on the history list. switch (string) case str1: ... breaksw ... default: ... Printed 7/25/83 16 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) breaksw endsw 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. time time command 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. umask umask 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. unalias 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. unhash Use of the internal hash table to speed location of executed programs is disabled. unset 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. wait All child processes are waited for. It the shell is interactive, then an interrupt can disrupt the wait, at Printed 7/25/83 17 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) which time the shell prints names and process numbers of all children known to be outstanding. while (expr) ... end 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. @ @ 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++'. Pre-defined variables The following variables have special meaning to the shell. Of these, _a_r_g_v, _c_h_i_l_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_h_i_l_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. The shell copies the environment variable PATH into the variable _p_a_t_h, and copies the value back into the environ- ment whenever _p_a_t_h is set. Thus is is not necessary to worry about its setting other than in the file ._c_s_h_r_c as inferior _o_l_d_c_s_h processes will import the definition of _p_a_t_h from the environment. (It could be set once in the ._l_o_g_i_n except that commands through _n_e_t(1) would not see the defin- ition.) Printed 7/25/83 18 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) argv 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. cdpath Gives a list of alternate directories searched to find subdirectories in _c_h_d_i_r com- mands. child The process number printed when the last com- mand was forked with `&'. This variable is _u_n_s_e_t when this process terminates. echo Set when the -x 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. histchars Can be assigned a two character string. The first character is used as a history charac- ter in place of ``!'', the second character is used in place of the ``^'' substitution mechanism. For example, ``set histchars=",;"'' will cause the history char- acters to be comma and semicolon. history 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. home The home directory of the invoker, initial- ized from the environment. The filename expansion of `~' refers to this variable. ignoreeof 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. mail The files where the shell checks for mail. This is done after each command completion which will result in a prompt, if a specified interval has elapsed. The shell says `You have new mail.' if the file exists with an Printed 7/25/83 19 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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. noclobber 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. noglob 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. nonomatch 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. path 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 -c nor the -t 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, it may be necessary to give the _r_e_h_a_s_h or the commands may not be found. prompt 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 Printed 7/25/83 20 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) unless a preceding `\' is given. Default is `% ', or `# ' for the super-user. shell 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. status 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'. time 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. verbose Set by the -v command line option, causes the words of each command to be printed after history substitution. Non-builtin command execution 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. If it is given neither a -c nor a -t 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 -c or -t argument, and in any case for each directory component of _p_a_t_h which does not begin with a ``/'', the shell concaten- ates 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 Printed 7/25/83 21 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) 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 an 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. Argument list processing If argument 0 to the shell is `-' then this is a login shell. The flag arguments are interpreted as follows: -c Commands are read from the (single) following argument which must be present. Any remaining arguments are placed in _a_r_g_v. -e The shell exits if any invoked command terminates abnormally or yields a non-zero exit status. -f The shell will start faster, because it will neither search for nor execute commands from the file `.cshrc' in the invokers home directory. -i 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. -n Commands are parsed, but not executed. This may aid in syntactic checking of shell scripts. -s Command input is taken from the standard input. -t 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. -v 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. -x Causes the _e_c_h_o variable to be set, so that commands are echoed immediately before execution. -V Causes the _v_e_r_b_o_s_e variable to be set even before Printed 7/25/83 22 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) `.cshrc' is executed. -X Is to -x as -V is to -v. After processing of flag arguments if arguments remain but none of the -c, -i, -s, or -t 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. Signal handling The shell normally ignores _q_u_i_t signals. The _i_n_t_e_r_r_u_p_t and _q_u_i_t signals are ignored for an invoked command if the com- mand is followed by `&'; otherwise the signals have the values which the shell inherited from its parent. The shells handling of interrupts can be controlled by _o_n_i_n_t_r. Login shells catch the _t_e_r_m_i_n_a_t_e signal; otherwise this sig- nal is passed on to children from the state in the shell's parent. In no case are interrupts allowed when a login shell is reading the file `.logout'. AUTHOR William Joy FILES ~/.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 `<<'. /dev/null Source of empty file. /etc/passwd Source of home directories for `~name'. LIMITATIONS Words can be no longer than 1024 characters. The number of characters in an argument varies from system to system. Early version 6 systems typically have 512 character limits while later version 6 and version 7 systems have 5120 char- acter limits. The number of arguments to a command which involves filename expansion is limited to 1/8'th the number of characters allowed in an argument list. Also command substitutions may substitute no more characters than are allowed in an argument list. Printed 7/25/83 23 OLDCSH(1) UNIX Programmer's Manual OLDCSH(1) To detect looping, the shell restricts the number of _a_l_i_a_s substitutions on a single line to 20. SEE ALSO access(2), execve(2), fork(2), pipe(2), signal(2), umask(2), wait(2), exec(3), a.out(5), environ(5), `An introduction to the C shell' BUGS Control structure should be parsed rather than being recog- nized as built-in commands. This would allow control com- mands to be placed anywhere, to be combined with `|', and to be used with `&' and `;' metasyntax. Commands within loops, prompted for by `?', are not placed in the _h_i_s_t_o_r_y list. 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. Some commands should not touch _s_t_a_t_u_s or it may be so tran- sient as to be almost useless. Oring in 0200 to _s_t_a_t_u_s on abnormal termination is a kludge. In order to be able to recover from failing _e_x_e_c commands on version 6 systems, the new command inherits several open files other than the normal standard input and output and diagnostic output. If the input and output are redirected and the new command does not close these files, some files may be held open unnecessarily. There are a number of bugs associated with the importing/exporting of the PATH. For example, directories in the path using the ~ syntax are not expanded in the PATH. Unusual paths, such as (), can cause oldcsh to core dump. This version of _o_l_d_c_s_h does not support or use the process control features of the 4th Berkeley Distribution. It con- tains a number of known bugs which have been fixed in the process control version. Printed 7/25/83 24