csh(1) csh(1)NAME csh - runs the C shell, a command interpreter with C-like syntax SYNOPSIS csh [-c] [-e] [-f] [-i] [-n] [-s] [-t] [-v] [-V] [-x] [-X] [arg]... ARGUMENTS arg Specifies the program to run through the shell. -c Reads commands from the (single) following argument, which must be present. Any remaining arguments are placed in argv. -e Exits the shell if any invoked command terminates abnormally or yields a nonzero exit status. -f Starts the shell faster because it will neither search for nor execute commands from the file .cshrc in the invoker's home directory. -i Causes the shell to be 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 aids in syntactic checking of shell scripts. -s Takes the command input from the standard input. -t Reads a single line of input and executes it. A \ may be used to escape the newline at the end of this line and continue onto another line. -v Causes the verbose variable to be set, with the effect that command input is echoed after history substitution. -V Causes the verbose variable to be set even before .cshrc is executed. -x Causes the echo variable to be set, so that commands are echoed immediately before execution. -X Causes the echo variable to be set even before .cshrc is executed. DESCRIPTION csh is a command language interpreter incorporating a history mechanism (see ``History Substitutions''), job January 1992 1
csh(1) csh(1)control facilities (see ``Jobs''), and a C-like syntax. In order to use its job control facilities, users of csh must enable the generation of suspend characters with stty(1). An instance of csh begins by executing commands from the file .cshrc in the home directory of the invoker. If this is a login shell, then it also executes commands from the file .login (also in the home directory). It is typical for users on CRT's to put the tset(1) command in their .login file. In the normal 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 words. 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 user's home directory. Lexical Structure The shell splits input lines into words at blanks and tabs, with the following exceptions. The characters &, |, ;, <, >, (, and ) 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 " characters, a newline preceded by a \ gives a true newline character. When the shell's input is not a terminal, the character # introduces a comment that continues to the end of the input line. It is prevented this special meaning when preceded by \ and when using `, ', and " quotation. Commands 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 pipelines 2 January 1992
csh(1) csh(1)may be separated by ;, and are then executed sequentially. 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, and so forth). It is also possible to separate pipelines with || or &&, indicating, as in the C language, that the second is to be executed only if the first fails or succeeds, respectively (see ``Expressions''). Jobs The shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with &, the shell prints a line that looks like [1] 1234 indicating that the job that 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 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 bg command, or run some other commands and then eventually bring the job back into the foreground with the foreground command fg. A CONTROL-Z takes effect immediately and is like an interrupt in that pending output and unread input are discarded when it is typed. There is another special key, CONTROL-Y, which does not generate a stop signal until a program attempts to read(2) it. This can usefully be typed ahead when you have prepared some commands for a job that you wish to stop after the program 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 giving the command ``stty tostop''. If you set this tty option, then background jobs will stop when they try to produce output as 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 January 1992 3
csh(1) csh(1)%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 ex(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 string, 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 history mechanism (described later), %% is also a synonym for the current job. Status Reporting 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 notify, the shell will notify you immediately of changes of status in background jobs. There is also a shell command notify, which marks a single process so that its status changes will be immediately reported. By default, notify 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 jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the suspended jobs will be terminated. Substitutions In this section, various transformations that the shell performs on the input are described, in the order in which they occur. History Substitutions History substitutions place words from previous command input in 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 anywhere in the input stream (with the proviso that 4 January 1992
csh(1) csh(1)they do not nest). This ! may be preceded by a \ to prevent its special meaning; for convenience, 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 that 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 that consist of one or more words are saved on the history list. The history substitutions reintroduce sequences of words from these saved commands into the input stream. The size of this list is controlled by the history variable; the previous command is always retained, regardless of its value. Commands are numbered sequentially from 1. For definiteness, consider the following output from the history command 9 write zach 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 prompt 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 !wri for event 9, or by a string contained in a word in the command as in !?zach? also referring to event 9. These forms, without further modification, simply reintroduce the words of the specified events, each separated by a single blank. As a special case !! refers to the previous command; thus !! alone is essentially a redo. 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 the command) word being 0, the second word (first argument) being 1, and so forth. The basic word designators are 0 first (command) word n nth argument ^ first argument, that is, 1 January 1992 5
csh(1) csh(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 ^, $, *, -, or %. After the optional word designator can be placed a sequence of modifiers, each preceded by a :. The following modifiers are defined: h Remove a trailing pathname component, leaving the head. r Remove a trailing .xxx component, leaving the root name. e Remove all but the extension .xxx part. s/l/r/ Substitute l for r. t Remove all leading pathname components, leaving the tail. & Repeat the previous substitution. g Apply the change globally, prefixing the above, for example g&. p Print the new command but do not execute it. q Quote the substituted words, preventing further substitutions. x Like q, but break into words at blanks, tabs, and newlines. Unless preceded by a g, the modification is applied only to the first modifiable word. With substitutions, it is an error for no word to be applicable. 6 January 1992
csh(1) csh(1)The left side of substitutions are not regular expressions in the sense of the editors, but rather strings. Any character may be used as the delimiter in place of /; a \ quotes the delimiter into the l and r strings. The character & on the right side is replaced by the text from the left. A \ quotes & also. A null l uses the previous string either from an l or from a contextual scan string s in !?s?. The trailing delimiter in the substitution may be omitted if a newline follows immediately, as may the trailing ? in a contextual scan. A history reference may be given without an event specification, for example !$. In this case the reference is to the previous command unless a previous history reference occurred on the same line, in which case this form repeats the previous 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 nonblank character of an input line is a ^. This is equivalent to !:s^, providing a convenient shorthand 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 characters that 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 " may be expanded as described later. In both cases the resulting text becomes (all or part of) a single word; only in one special case (see ``Command Substitution'') does a " quoted string yield parts of more than one word; ' quoted strings never do. Alias Substitution The shell maintains a list of aliases, which can be established, displayed, and modified by the alias and unalias 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 that 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. January 1992 7
csh(1) csh(1)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 tim would map to grep tim /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 say alias print 'pr \!* | lpr ' to make a command that uses pr to send 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 or referred to by the shell. For instance, the argv variable is an image of the shell's argument list, and words of this variable's value are referred to in special ways. The values of variables may be displayed and changed by using the set and unset 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 verbose variable is a toggle that causes command input to be echoed. The setting of this variable results from the -v option. Other operations treat variables numerically. The @ command permits numeric calculations to be performed and the result assigned to a variable. Variable values are, however, always represented as (zero or more) strings. For the purposes of numeric operations, the null string is considered 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 double quotes where it always occurs, and within single quotes where it never occurs. Strings quoted by ` are interpreted later (see ``Command Substitution''), so $ substitution does not occur 8 January 1992
csh(1) csh(1)there until later, if at all. A $ is passed unchanged if followed 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 at 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 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 that is not set. $name ${name} Are replaced by the words of the value of variable name, each separated by a blank. Braces insulate name from following characters that would otherwise be part of it. Shell variables have names consisting of up to 18 letters and digits starting with a letter. The underscore character is considered a letter. If name is not a shell variable, but is set in the environment, then that value is returned (but : modifiers and the other forms given later are not available in this case). $name[selector] ${name[selector]} May be used to select only some of the words from the value of name. The selector is subjected to $ substitution and may consist of a single number or two numbers separated by a -. The first word of a 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 $#name. The selector * selects all words. It is not an error for a range to be empty if the second argument is omitted or in range. January 1992 9
csh(1) csh(1)$#name ${#name} Gives the number of words in the variable name. 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 modifiers must appear within the braces. Note: The current implementation 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 known, 0 if it is not. $$ Substitutes 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. Command and Filename Substitution The remaining substitutions, command and filename substitution, are applied selectively to the arguments of built-in commands. This means that portions of expressions that are not evaluated are not subjected to these expansions. For commands that 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 performed, and in a child of the main shell. 10 January 1992
csh(1) csh(1)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 ", 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 substitution to yield only part of a word, even if the command outputs 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 globbing. This word is then regarded as a pattern and replaced with an alphabetically sorted list of filenames that match the pattern. In a list of words specifying filename substitution, it is an error if no pattern matches an existing filename, but it is not required that each pattern 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, that is, as ~, it expands to the invokers home directory as reflected in the value of the variable home. When followed by a name consisting of letters, digits and - characters, the shell searches for a user with that name and substitutes the home directory; thus ~paul might expand to /usr/paul and ~paul/chmach to /usr/paul/chmach. If the character ~ is followed by a character other than a letter or / appears, but not at the beginning of a word, it is left undisturbed. The metanotation a{b,c,d}e is 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 January 1992 11
csh(1) csh(1)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 special 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 name (which is first variable, command, and filename expanded) as the standard input. << word Read the shell input up to a line that is identical to word. word is not subjected to variable, filename, or command substitution, and each input line is compared to word before any substitutions are done on this input line. Unless a quoting \, ", ', or ` appears in word, variable and command substitution is performed on the intervening lines, allowing \ to quote $, \, and `. Commands that are substituted have all blanks, tabs, and newlines preserved, except for the final newline that 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 name is used as standard output. If the file does not exist, then it is created; if the file exists, it is truncated and its previous contents are lost. If the variable noclobber is set, then either the file must not exist or be a character special file (for example, a terminal 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 12 January 1992
csh(1) csh(1)check. The forms involving & route the diagnostic output as well as the standard output into the specified file. name is expanded in the same way as < input filenames are. >> name >>& name >>! name >>&! name Uses file name as standard output like >, but places output at the end of the file. If the variable noclobber is set, then it is an error for the file not to exist unless one of the ! forms is given. Otherwise 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 that 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 command run detached is not modified to be the empty file /dev/null; rather the standard input remains as the original 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 ``Jobs.'') Diagnostic output may be directed through a pipe with the standard output. Simply use the form |& rather than just |. Expressions A number of the built-in commands (to be described subsequently) take expressions, in which the operators are similar to those of C, with the same precedence. These expressions appear in the @, exit, if, and while commands. The following operators are available: || && | ^ & == != =~ !~ <= >= < > << >> + - * / % ! ~ ( ) Here the precedence increases to the right with those on the same line having equal precedence: == != =~ !~ <= >= < > << >> + - January 1992 13
csh(1) csh(1)* / % The ==, !=, =~, and !~ operators compare their arguments as strings; all others operate on numbers. The operators =~ and !~ are like == and != except that the right side is a pattern (containing, for example, *, ?, and instances of [...]) against which the left operand is matched. This reduces the need for use of the switch statement in shell scripts when all that is really needed is pattern matching. Strings that 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 that are syntactically significant to the parser & | < > ( ) they should be surrounded by spaces. Also available in expressions as primitive operands are command 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, that is 0. Command executions succeed, returning true, that is 1, if the command exits with status 0; otherwise they fail, returning false, that is 0. If more detailed status information is required then the command should be executed outside of an expression and the variable status examined. Control Flow The shell contains a number of commands that 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. 14 January 1992
csh(1) csh(1)The foreach, switch, and while statements, as well as the if-then-else form of the if statement require that the major keywords appear in a single simple command on an input line as shown later. 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 nonseekable inputs.) Built-in Commands Built-in commands are executed within the shell. If a built-in command occurs as any component of a pipeline except the last then it is executed in a subshell. 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 wordlist as the alias of name; wordlist is command- and filename-substituted. name is not allowed to be alias or unalias. alloc Shows the amount of dynamic core in use, broken down into used and free core, and the address of the last location in the heap. alloc used with an argument shows each used and free block on the internal dynamic memory chain indicating 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 modified version of the system memory allocator. bg bg %job ... Puts the current or specified jobs into the background, continuing them if they were stopped. break Causes execution to resume after the end of the nearest enclosing foreach or while. The remaining commands on the current line are executed. Multilevel breaks are thus possible by writing them all on one line. breaksw Causes a break from a switch, resuming after the endsw. case label: A label in a switch statement as discussed later under January 1992 15
csh(1) csh(1)switch. cd cd name chdir chdir name Changes the shell's working directory to directory name. If no argument is given, then change to the home directory of the user. If name is not found as a subdirectory of the current directory (and does not begin with /, ./, or ../), then each component of the variable cdpath is checked to see if it has a subdirectory name. Finally, if all else fails but name is a shell variable whose value begins with /, then its value is tried to see if it is a directory. continue Continues execution of the nearest enclosing while or foreach. The rest of the commands on the current line are executed. default: Labels the default case in a switch statement. The default should come after all case labels. dirs Prints the directory stack; the top of the stack is at the left, the first directory in the stack being the current directory. echo wordlist echo -n wordlist The specified words are written to the shell's standard output, separated by spaces and terminated with a newline unless the -n option is specified. else end endif endsw See the description of the foreach, if, switch, and while statements later in this section. eval arg... The arguments are read as input to the shell (as in sh(1)) and the resulting command(s) is executed in the context 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 tset(1) for an example of using eval. exec command 16 January 1992
csh(1) csh(1)The specified command is executed in place of the current shell. exit exit(expr) The shell exits either with the value of the status variable (first form) or with the value of the specified expr (second form). fg fg %job... Brings the current or specified jobs into the foreground, continuing them if they were stopped. foreach name (wordlist) ... end The variable name is successively set to each member of wordlist and the sequence of commands between this command and the matching end are executed. (Both foreach and end must appear singly on separate lines.) The built-in command continue may be used to continue the loop prematurely and the built-in command break 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 executed. If you make a mistake typing in a loop at the terminal, you can interrupt it. glob wordlist Like echo but no \ escapes are recognized and words are delimited by null characters in the output. Useful for programs that wish to use the shell to filename-expand a list of words. goto word The specified word 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. hashstat Prints a statistics line indicating how effective the internal hash table has been at locating commands (and avoiding any exec). An exec is attempted for each component of the path where the hash function indicates a possible hit, and in each component that does not begin with a /. history history n January 1992 17
csh(1) csh(1)history -r n history h n Displays the history event list; if n is given, only the n most recent events are printed. The -r option reverses the order of printout to be most recent first rather than oldest first. The -h option causes the history list to be printed without leading numbers and is used to produce files suitable for sourcing using the -h option to source. if (expr) command If the specified expr evaluates true, then the single command with arguments is executed. In the interactive shell, the if statement can only accept one simple command after the expr and in the same line as expr. Variable substitution on command happens early, at the same time it does for the rest of the if command. The command must be a simple command, not a pipeline, a command list, or a parenthesized command list. Input/output redirection occurs even if expr is false, when command is not executed (this is a bug). if (expr) then ... else if (expr2) then ... else ... endif If the specified expr is true, then the first command is executed. In the interactive shell, the if then statement can only accept one simple command after then. This command must be specified on the same line as then. If the specified expr2 is true, then the command to the else or else if are executed, and so forth. Any number of else if pairs are possible; only one endif is needed. The else part is likewise optional. (The words else and endif must appear at the beginning of input lines; the if must appear alone on its input line or after an else.) jobs jobs -l Lists the active jobs; the -l option lists process ID's in addition to the normal information. kill %job kill -sig %job... kill pid kill -sig pid... kill -l Sends either the TERM (terminate) signal or the 18 January 1992
csh(1) csh(1)specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in /usr/include/signal.h, stripped of the prefix SIG). The signal names are listed by kill -l. There is no default; just saying kill does not send a signal to the current job. A pid of 0 means the current process (that is, this invocation of the C shell). Consequently, kill -9 0 terminates the current C shell and possibly logs you off. If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process will be sent a CONT (continue) signal as well. login Terminates a login shell, replacing it with an instance of /bin/login. This is one way to log off, included for compatibility with sh(1). logout Terminates a login shell. Especially useful if ignoreeof is set. nice nice +number nice command nice +number command The first form sets the nice for this shell to 4. The second form sets the nice to the given number. The final two forms run command at priority 4 and number respectively. The superuser may specify negative niceness by using nice -number ... Command is always executed in a subshell, and the restrictions placed on commands in simple if 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. All processes detached with & are run effectively without hangups. notify notify %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 notify is set. January 1992 19
csh(1) csh(1)onintr onintr - onintr label Controls the action of the shell on interrupts. The first form restores the default action of the shell on interrupts that are 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 onintr have no meaning and interrupts continue to be ignored by the shell and all invoked commands. popd popd +n Pops the directory stack, returning to the new top directory. With the argument +n, popd discards the nth entry in the stack. The elements of the directory stack are numbered from 0 starting at the top. pushd pushd name pushd +n With no arguments, pushd exchanges the top two elements of the directory stack. Given a name argument, pushd changes to the new directory (like cd) and pushes the old current working directory (as in csw) onto the directory stack. With a numeric argument, pushd rotates the nth argument of the directory stack around to be the top element and changes into it. The members of the directory stack are numbered from the top starting at 0. rehash Causes the internal hash table of the contents of the directories in the path variable to be recomputed. This is needed if new commands are added to directories in the path 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 command (which is subject to the same restrictions as the command in the one line if statement above) is executed count times. I/O redirections occur exactly once, even if count is 0. 20 January 1992
csh(1) csh(1)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 that have other than a single word as value print as a parenthesized word list. The second form sets name to the null string. The third form sets name to the single word. The fourth form sets the index component of name to word; this component must already exist. The final form sets name to the list of words in wordlist. 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 Sets the value of the environment variable name to be value, a single string. The most commonly used environment variables USER, TERM, and PATH are automatically imported to and exported from the csh variables user, term, and path; there is no need to use setenv for these. shift shift variable The members of argv are shifted to the left, discarding argv[1]. It is an error for argv not to be set or to have less than one word as value. The second form performs the same function on the specified variable. source name source -h name The shell reads commands from name. source commands may be nested; if they are nested too deeply, the shell may run out of file descriptors. An error in a source at any level terminates all nested source commands. Normally, input during source commands is not placed on the history list; the -h option causes the commands to be placed in the history list without being executed. stop %job ... Stops the current or specified job that is executing in the background. suspend Causes the shell to stop in its tracks, much as if it had been sent a stop signal with CONTROL-Z. This is January 1992 21
csh(1) csh(1)most often used to stop shells started by su(1). switch (string) case str1: ... breaksw ... default: ... breaksw endsw Each case label is successively matched against the specified string, which is first command- and filename-expanded. The file metacharacters *, ?, and [...] may be used in the case labels, that 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 breaksw causes execution to continue after the endsw; 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 endsw. 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 summary as described under the time 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 there to be nothing to unalias. unhash Use of the internal hash table to speed location of executed programs is disabled. unset pattern 22 January 1992
csh(1) csh(1)All variables whose names match the specified pattern are removed. Thus all variables are removed by unset *, which has noticeably distasteful side-effects. It is not an error for nothing to be unset. unsetenv pattern Removes all variables whose name match the specified pattern from the environment. See also the setenv command and printenv(1). wait All background jobs are waited for. If 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. while (expr) ... end While the specified expression evaluates nonzero, the commands between the while and the matching end are evaluated. break and continue may be used to terminate or continue the loop prematurely. (The while and end must appear alone on their input lines.) Prompting occurs here, the first time through the loop, as for the foreach 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 variables. The second form sets the specified name to the value of expr. If the expression contains <, >, &, or |, then at least this part of the expression must be placed within (). The third form assigns the value of expr to the index argument of name. Both name and its index component must already exist. The operators *=, +=, and so forth, are available as in C. The space separating the name from the assignment operator is optional. Spaces are, however, mandatory in separating components of expr that would otherwise be single words. Special postfix ++ and -- operators increment and decrement name respectively; for example @ i++. January 1992 23
csh(1) csh(1)Predefined and Environment Variables The following variables have special meaning to the shell. Of these, argv, cwd, home, path, prompt, shell, and status are always set by the shell. Except for cwd and status, this setting occurs only at initialization; these variables then will not be modified except explicitly by the user. This shell copies the environment variable USER into the variable user, TERM into term, and HOME into home, 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 .cshrc, as inferior csh processes will import the definition of path from the environment and re-export it if you change it. argv Set to the arguments to the shell, it is from this variable that positional parameters are substituted; that is, $1 is replaced by $argv[1], and so forth. cdpath Gives a list of alternate directories searched to find subdirectories in chdir commands. cwd The full pathname of the current directory. echo Set when the -x command line option is given. echo causes each command and its arguments to be echoed just before it is executed. For nonbuilt-in commands, all expansions occur before echoing. Built-in commands are echoed before command and filename substitution, since these substitutions are then done selectively. histchars 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. history Can be given a numeric value to control the size of the history list. Any command that has been referenced in this many events will not be discarded. Values of history that are too large may run the shell out of memory. The last executed command is always saved on the history list. 24 January 1992
csh(1) csh(1)home The home directory of the invoker, initialized from the environment. The filename expansion of ~ refers to this variable. ignoreeof If set, the shell ignores end-of-file from input devices that 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 that will result in a prompt, if a specified interval has elapsed. The shell says You have new mail if the file exists with an access time not greater than its modification time. If the first word of the value of mail is numeric, it specifies a different mail checking interval, in seconds, than the default, which is 10 minutes. If multiple mail files are specified, then the shell says New mail in name when there is mail in the file name. noclobber As described in the section ``Input/Output,'' restrictions are placed on output redirection to ensure 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 that 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 if a filename expansion does not match any existing files; rather the primitive pattern is returned. It is still an error for the primitive pattern to be malformed, that is, echo [ still gives an error. notify If set, the shell notifies asynchronously of January 1992 25
csh(1) csh(1)job completions. The default is to present job completions just before printing a prompt. 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 path variable, then only full pathnames will execute. The usual search path is ., /bin, and /usr/bin, but this may vary from system to system. For the superuser, the default search path is /etc, /bin, and /usr/bin. A shell that is given neither the -c nor the -t option will normally hash the contents of the directories in the path variable after reading .cshrc, and each time the path variable is reset. If new commands are added to these directories while the shell is active, it may be necessary to give the rehash or the commands may not be found. prompt The string that is printed before each command is read from an interactive terminal input. If an ! appears in the string, it will be replaced by the current event number unless a preceding \ is given. Default is % or # for the superuser. savehist a numeric value is given to control the number of entries of the history list that are saved in ~/.history when the user logs out. Any command that has been referenced in that number of events will be saved. During start up the shell sources ~/.history into the history list, enabling history to be saved across logins. Values of savehist that are too large will slow down the shell during start up. shell The file in which the shell resides. This is used in forking shells to interpret files that have execute bits set, but which are not executable by the system. (See the description of ``Nonbuilt-in Command Execution'' later.) 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. Built-in commands that fail return exit status 1; all other built-in 26 January 1992
csh(1) csh(1)commands set status 0. time Controls automatic timing of commands. If set, then any command that takes more than this many cpu seconds will cause a line to be printed when it terminates. This line shows user, system, and real times and a utilization percentage that is the ratio of user plus system times to real time verbose Set by the -v option. Causes the words of each command to be printed after history substitution. Nonbuilt-in Command Execution When a command to be executed is found to not be a built-in command, the shell attempts to execute the command via execve(2). Each word in the variable path 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 exec 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 unhash), or if the shell was given a -c or -t argument (and in any case for each directory component of path that does not begin with a /), the shell concatenates with the given command name to form a pathname of a file, which it then attempts to execute. Parenthesized commands are always executed in a subshell. Thus, (cd ; pwd) ; pwd prints the home directory, leaving you where you were (printing this after the home directory), while cd ; pwd leaves you in the home directory. Parenthesized commands are most often used to prevent chdir 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 containing shell commands and a new shell is spawned to read it. If there is an alias for shell, then the words of the alias will be prefixed to the argument list to form the shell January 1992 27
csh(1) csh(1)command. The first word of the alias should be the full pathname of the shell (for example $shell). Note that this is a special, late occurring, case of alias substitution, and only allows words to be prefixed to the argument list without modification. Argument List Processing If argument 0 to the shell is - then this is a login shell. After processing of arguments, if arguments remain but none of the -c, -i, -s, or -t options were 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 the standard Bourne shell (/bin/sh), 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 #; that is, if the script does not start with a comment. Remaining arguments initialize the variable argv. Signal Handling The shell normally ignores quit signals. Jobs running detached (either by & or the bg or %...& commands) are immune to signals generated from the keyboard, including hangups. Other signals have the values that the shell inherited from its parent. The shells handling of interrupts and terminate signals in shell scripts can be controlled by onintr. Login shells catch the terminate signal; otherwise this signal 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. LIMITATIONS Words can be no longer than 1024 characters. The system limits argument lists to 10240 characters. The number of arguments to a command that involves filename expansion is limited to 1/6th 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 alias substitutions on a single line to 20. 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 (that is, wrong) as the job may have changed directories internally. Shell built-in functions are not stoppable/restartable. Command sequences of the form a ; b ; c 28 January 1992
csh(1) csh(1)are also not handled gracefully when stopping is attempted. If you suspend b, the shell will then immediately execute c. This is especially noticeable if this expansion results from an alias. It suffices to place the sequence of commands in () to force it to a subshell. (a ; b ; c) Control over tty output after processes are started is primitive; 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 control. Alias substitution is most often used to simulate shell procedures; shell procedures should be provided rather than aliases. Commands within loops, prompted for by ?, are not placed in the history list. Control structure should be parsed rather than recognized as built-in commands, allowing control commands to be placed anywhere, to be combined with |, and to be used with &, and ; metasyntax. It should be possible to use the : modifiers on the output of command substitutions. All and more than one : modifier should be allowed on $ substitutions. Symbolic links fool the shell. In particular, dirs and cd .. don't work properly once you've crossed through a symbolic link. FILES /bin/csh Executable file ~/.cshrc File that is read at the beginning of execution by each shell /etc/cshrc Global file that is read by the login shell before ~/.cshrc ~/.login File that is read by the login shell after .cshrc at login. ~/.logout File that is read by the login shell, at logout /bin/sh Standard shell file, for shell scripts not starting with a #. January 1992 29
csh(1) csh(1)/tmp/sh* Temporary file for <<. /etc/passwd Source of home directories for ~name. SEE ALSO ksh(1), sh(1) access(2), exec(2), fork(2), pipe(2), sigvec(2), umask(2), wait(2), killpg(3N), a.out(4), environ(5), tty(7) in A/UX Programmer's Reference ``C Shell Reference'' in A/UX Shells and Shell Programming 30 January 1992