sh(1) - Unix First Edition Manual Page
11/3/71SH (I)
NAME sh -- shell (command interpreter)
SYNOPSIS sh [ name [ arg1 ... [ arg9 ] ] ]
DESCRIPTION sh is the standard command interpreter. It is the programwhich reads and arranges the execution of the command lines


typed by most users. It may itself be called as a commandto interpret files of command lines. Before discussing the arguments to the shell used as a command, the structure ofcommand lines themselves will be given.


Command lines are sequences of commands separated bycommand delimiters. Each command is a sequence of non--blank command arguments separated by blanks. The first argumentspecifies the name of a command to be executed. Except for certain types of special arguments discussed below, thearguments other than the command name are simply passed to the invoked command. If the first argument represents the path name of anexecutable file, it is invoked; otherwise the string "/bin/" is prepended to the argument. (In this way thestandard commands, which reside in "/bin," are found.) If this search too fails a diagnostic is printed. The remaining non--special arguments are simply passed tothe command without further interpretation by the shell.


There are three command delimiters: the new line, ";" , and"&". The semicolon ";" specifies sequential execution of


the commands so separated; that is,


coma; comb causes the execution first of command coma, then of comb.The ampersand "&" causes simultaneous execution:


coma & comb causes coma to be called, followed immediately by combwithout waiting for coma to finish. Thus coma and comb execute simultaneously. As a special case,


coma & causes coma to be executed and the shell immediately torequest another command without waiting for coma.


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Two characters cause the immediately following string to beinterpreted as a special argument to the shell itself, not passed to the command. An argument of the form arg" causes file"arg" to be used as the standard output file for the given command. If any argument contains either of the characters "?" or"*" , it is treated specially as follows. The current directory is searched for files which match the givenargument. The character "*" in an argument matches any string of characters in a file name (including the nullstring); ? matches any single character in a file name. Other argument characters match only the same character inthe file name. For example, "*" matches all file names; "?" matches all one--character file names; "ab*.s" matches allfile names beginning with "ab" and ending with ".s".


If the argument with "*" or "?" also contains a "/", aslightly different procedure is used: instead of the current directory, the directory used is the one obtainedby taking the argument up to the last "/" before a "*" or "?". The matching process matches the remainder of theargument after this "/" against the files in the derived directory. For example:, "/usr/dmr/a*.s" matches all filesin directory /usr/dmr which begin with "a" and end with ".s" In any event, a list of names is obtained which match theargument. This list is sorted into alphabetical order, and the resulting sequence of arguments replaces the singleargument containing the "*" or "?". The same process is carried out for each argument with a * or ?" (the resultinglists are not merged) and finally the command is called with the resulting list of arguments..


For example: directory /usr/dmr contains the files al * s,a2.s, ..., a9.s. From any directory, the command


as /usr/dmr/a?.s calls as with arguments /usr/dmr/al.s, /usr/dmr/a2.s, .../usr/dmr/a9.s in that order.


The character "\" causes the immediately followingcharacter to lose any special meaning it may have to the shell; in this way < , , and other characters meaningful tothe shell may be passed as part of arguments. A special case of


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this feature allows the continuation of commands onto morethan one line: a new--line preceded by "\" is translated into a blank.


Sequences of characters enclosed in double (") or single(') quotes are also taken literally.


When the shell is invoked as a command, it has additionalstring processing capabilities. Recall that the form in which the whell is invoked is


sh [ name [ arg1 ... [ arg9 ] ] ] The name is the name of a file which will be read andinterpreted. If not given, this subinstance of the shell will continue to read the standard input file. In the file, character sequences of the form "$n", where nis a digit 0, ..., 9, are replaced by the nth argument to the invocation of the shell (arg ). $0" is replaced byname.


An end--of--file in the shell's input causes it to exit. Aside effect of this fact means that the way to log out from UNIX is to type an end of file.
FILES /etc/glob
SEE_ALSO [reference], which gives the theory of operation of theshell.


DIAGNOSTICS "?", in case of any difficulty. The most common problem isinability to find the given command. Others: input file


("<") cannot be found; no more processes can be created(this will alleviate itself with the passage of time). Note that no diagnostic is given for inability to create anoutput (">") file; the standard output file has already been closed when the condition is discovered and there isno place to write the diagnostic.


If a "*" or "?" is used, the "glob" routine is invoked; ittypes "No command" if it cannot find the given command, and "No match" if there were no files which matched an argumentwith "?" or "*".


BUGS Better diagnostics should be provided. If a "*" or "?" isused, the command must be in /bin (Not, for example, in the


user's directory.) This is actually a glob bug.
OWNER dmr, ken