diff options
Diffstat (limited to 'static/unix-v10/man1/sh.1')
| -rw-r--r-- | static/unix-v10/man1/sh.1 | 386 |
1 files changed, 386 insertions, 0 deletions
diff --git a/static/unix-v10/man1/sh.1 b/static/unix-v10/man1/sh.1 new file mode 100644 index 00000000..114920c2 --- /dev/null +++ b/static/unix-v10/man1/sh.1 @@ -0,0 +1,386 @@ +.pa 1 +.he 'SH (I)'1/15/73'SH (I)' +.ti 0 +NAME sh -- shell (command interpreter) +.sp +.ti 0 +SYNOPSIS sh__ [ name [ arg\d1\u ... [ arg\d9\u ] ] ] +.sp +.ti 0 +DESCRIPTION +.br +.in 8 +sh__ +is the standard command interpreter. +It is the program which reads and arranges the execution of +the command lines typed by most users. +It may itself be called as a command to interpret +files of commands. +Before discussing the arguments to the shell +used as a command, the structure of command +lines themselves will be given. + +.ul +Command lines +.sp +Command lines are sequences of commands separated by command +delimiters. +Each command is a sequence of non-blank command arguments +separated by blanks. +The +first argument specifies the name of a command to be +executed. Except for certain types of special +arguments discussed below, the arguments +other than the command name are passed +without interpretation to the invoked +command. +.sp +If the first argument is the name of an executable +file, it is invoked; +otherwise the string "/bin/" is prepended to the argument. +(In this way most standard commands, +which reside in "/bin", are found.) +If no such command is found, +the string "/usr" is further prepended +(to give "/usr/bin/command") and another attempt +is made to execute the resulting +file. +(Certain "overflow" commands +live in "/usr/bin".) If +the "/usr/bin" file exists, but is not +executable, it is used by the shell as +a command file. +That is to say it is executed +as though it were typed from the console. +If all attempts fail, a diagnostic is printed. +.sp +The remaining non-special arguments are simply passed to the command +without further interpretation by the shell. +.sp +.ul +Command delimiters + +There are three command delimiters: the new-line, ";", and "&". +The semicolon ";" specifies sequential execution of the commands +so separated; that is, +.sp + coma; comb +.sp +causes the execution first of command coma____, then of comb____. +The ampersand "&" causes simultaneous execution: +.sp + coma & comb +.sp +causes coma____ to be called, +followed immediately by comb____ without waiting for coma____ to finish. +Thus coma____ and comb____ +execute simultaneously. As a special case, +.sp + coma & +.sp +causes coma____ to be executed and the shell immediately +to request another command without waiting for coma____. +.a +.sp +.ul +Termination Reporting +.sp +If a command (not followed by "&") terminates abnormally, +a message is printed. +(All terminations other than exit and interrupt +are considered abnormal.) +The following is a list of the abnormal +termination messages: +.sp + Bus error + Trace/BPT trap + Illegal instruction + IOT trap + Power fail trap + EMT trap + Bad system call + Quit + PIR trap + Floating exception + Memory violation + Killed + User I/O + Error +.sp +If a core image is produced, +" -- Core dumped" is appended to the appropriate message. +.sp +.ul +Redirection of I/O + +Three character sequences cause the immediately following string +to be interpreted as a special argument to the shell itself, not +passed to the command. + +An argument of the form "<arg" causes the file arg___ +to be used as the standard input file of the given command. + +An argument of the form ">arg" causes file "arg" to be used +as the standard output file for the given command. +"Arg" is created if it did not exist, and in any case is truncated +at the outset. + +An argument of the form ">>arg" causes file "arg" to be used as the +standard output for the given command. If "arg" +did not exist, it is created; if it did exist, +the command output is appended to the file. + +.ul +Pipes and Filters + +A pipe____ is a channel such that information +can be written into one end of the pipe by one program, +and read at the other end by another program. +(See pipe____ (II)). A +filter______ is a program which reads the standard +input file, performs some transformation, +and writes the result on the standard output file. +By extending the syntax used +for redirection of I/O, a command line can +specify that the output produced by +a command be passed via a pipe +through another command which acts as a filter. +For example: + + command >filter> + +More generally, special arguments of the form + + >f\d1\u>f\d2\u>...> + +specify that output is to be passed successively +through the filters f\d1\u, f\d2\u, ..., +and end up on the standard output stream. +By saying instead + + >f\d1\u>f\d2\u>...>file + +the output finally ends up in file____. (The +last ">" could also have been a ">>" +to specify concatenation onto the end of file____.) + +In exactly analogous manner input filtering can +be specified via one of + + <f\d1\u<f\d2\u<...< + <f\d1\u<f\d2\u<...<file + +Both input and output filtering +can be specified in the same command, though not in the same +special argument. + +For example: + + ls >pr> + +produces a listing of the current directory with +page headings, while + + ls >pr>xx + +puts the paginated listing into the file xx. + +If any of the filters needs arguments, quotes can be used +to prevent the required blank characters from +violating the blankless +syntax of filters. +For example: + + ls >"pr -h 'My directory'"> + +uses quotes twice, once to protect the entire pr__ command, +once to protect the heading argument of pr__. +(Quotes are discussed fully below.) + +.ul +Generation of argument lists + +If any argument contains any of the characters "?", +"*" or '[', it is treated specially as follows. +The current directory is searched for files which match_____ +the given argument. + +The character "*" in an argument matches any string of characters +in a file name (including the null string). + +The character "?" matches any +single character in a file name. + +Square brackets "[...]" specify +a class of characters which +matches any single file-name character in the class. +Within the brackets, +each ordinary character is taken +to be a member of the class. +A pair of characters separated by "-" places +in the class +each character lexically greater than or equal to +the first and less than or equal to the second +member of the pair. + +Other characters match only the same character in +the file name. + +For example, "*" matches all file names; +"?" matches all one-character file names; "[ab]*.s" matches +all file names beginning with "a" or "b" and ending with ".s"; +"?[zi-m]" matches all two-character file names ending +with "z" or the letters "i" through "m". + +If the argument with "*" or "?" also contains a "/", a slightly +different procedure is used: instead of the current directory, +the directory used is the one obtained +by taking the argument up to the last "/" before a "*" or "?". +The matching process matches the remainder of the argument +after this "/" against the files in the derived directory. +For example: "/usr/dmr/a*.s" matches +all files in directory "/usr/dmr" which begin +with "a" and end with ".s". + +In any event, a list of names is obtained which match +the argument. This list is sorted into alphabetical order, +and the resulting sequence of arguments replaces the +single argument containing the "*", "[", or "?". +The same process is carried out for each argument +(the resulting lists are not___ merged) +and finally the command is called with the resulting list of +arguments. + +For example: directory /usr/dmr contains the files +a1.s, a2.s, ..., a9.s. From any directory, the command + + as /usr/dmr/a?.s + +calls as__ with arguments +/usr/dmr/a1.s, /usr/dmr/a2.s, ... +/usr/dmr/a9.s +in that order. +.sp +.ul +.ul +Quoting + +The character "\\" causes the immediately following character +to lose any special meaning it may have to the shell; in this +way "<", ">", and other characters meaningful to the +shell may be passed as part of arguments. +A special case of this feature allows the continuation of commands +onto more than one line: a new-line preceded by "\\" is translated +into a blank. +.sp +Sequences of characters enclosed in double (") or single (') +quotes are also taken literally. +.sp +.ul +Argument passing + +When the shell is invoked as a command, it has additional +string processing capabilities. +Recall that the form in which the shell is invoked is + + sh [ name [ arg\d1\u ... [ arg\d9\u ] ] ] + +The name____ is the name of a file which will be read and +interpreted. If not given, this subinstance of the shell +will continue to read the standard input file. + +In command lines in the file +(not in command input), +character sequences of the form "$n", where n_ is a digit 0, ..., 9, +are replaced by the n_th argument to the invocation +of the shell (arg\dn\u). +"$0" is replaced by name____. + +.ul +End of file + +An end-of-file in the shell's input causes it to exit. +A side effect of this fact means that the way to +log out from UNIX is to type an end of file. + +.ul +Special commands + +Two commands are treated specially by the shell. + +"Chdir" is done without +spawning a new process by executing the sys___ chdir_____ +primitive. + +"Login" is done by executing +/bin/login without creating a new process. + +These peculiarities are inexorably imposed +upon the shell by the basic structure +of the UNIX process control system. +It is a rewarding exercise to work +out why. + +.ul +Command file errors; interrupts + +Any shell-detected error, or an interrupt signal, +during the execution of a command file +causes the shell to cease execution of that file. + +.in 16 +.ti 0 +FILES /etc/glob, +which interprets "*", "?", and "[". +.sp +.ti 0 +SEE ALSO "The UNIX Time-sharing System", +which gives the theory of operation of the +shell. +.sp +.ti 0 +DIAGNOSTICS +.br +.in 8 +"Input not found", when a command file is +specified which cannot be read; +.br +"Arg count", if the number of arguments to the chdir pseudo-command +is not exactly 1, +or if "*", "?", or "[" is used inappropriately; +.br +"Bad directory", if the directory given in "chdir" cannot be +switched to; +.br +"Try again", if no new process can be created to execute +the specified command; +.br +""' imbalance", if single or double quotes are not matched; +.br +"Input file", if an argument after "<" cannot be read; +.br +"Output file", if an argument after ">" or ">>" cannot +be written (or created); +.br +"Command not found", if the specified command cannot be executed. +.br +"No match", if no arguments are generated for a command +which contains "*", "?", or "[". +.br +Termination messages described above. +.sp +.in 16 +.ti 0 +BUGS If any argument contains a quoted "*", +"?", or "[", then all instances of these characters +must be quoted. +This is because sh__ calls the glob____ routine whenever +an unquoted "*", "?", or "[" is noticed; +the fact that other instances of these characters occurred +quoted is not noticed by glob____. + +When output is redirected, +particularly through a filter, +diagnostics tend to be +sent down the pipe and are sometimes +lost altogether. |