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sh: Update TOUR and comments for some code changes, some of them old.
Also, improve some terminology in TOUR and comments.
This commit is contained in:
Jilles Tjoelker
parent
1fc317e374
commit
b98072777f
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=317882
77
bin/sh/TOUR
77
bin/sh/TOUR
@ -24,7 +24,7 @@ programs is:
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program input files generates
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------- ----------- ---------
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mkbuiltins builtins builtins.h builtins.c
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mkbuiltins builtins.def builtins.h builtins.c
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mknodes nodetypes nodes.h nodes.c
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mksyntax - syntax.h syntax.c
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mktokens - token.h
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@ -108,10 +108,12 @@ The text field of a NARG structure points to the text of the
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word. The text consists of ordinary characters and a number of
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special codes defined in parser.h. The special codes are:
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CTLVAR Variable substitution
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CTLENDVAR End of variable substitution
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CTLVAR Parameter expansion
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CTLENDVAR End of parameter expansion
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CTLBACKQ Command substitution
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CTLBACKQ|CTLQUOTE Command substitution inside double quotes
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CTLARI Arithmetic expansion
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CTLENDARI End of arithmetic expansion
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CTLESC Escape next character
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A variable substitution contains the following elements:
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@ -130,18 +132,31 @@ stitution. The possible types are:
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VSQUESTION|VSNUL ${var:?text}
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VSASSIGN ${var=text}
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VSASSIGN|VSNUL ${var:=text}
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VSTRIMLEFT ${var#text}
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VSTRIMLEFTMAX ${var##text}
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VSTRIMRIGHT ${var%text}
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VSTRIMRIGHTMAX ${var%%text}
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VSLENGTH ${#var}
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VSERROR delayed error
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In addition, the type field will have the VSQUOTE flag set if the
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variable is enclosed in double quotes. The name of the variable
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comes next, terminated by an equals sign. If the type is not
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VSNORMAL, then the text field in the substitution follows, ter-
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minated by a CTLENDVAR byte.
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variable is enclosed in double quotes and the VSLINENO flag if
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LINENO is being expanded (the parameter name is the decimal line
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number). The parameter's name comes next, terminated by an equals
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sign. If the type is not VSNORMAL (including when it is VSLENGTH),
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then the text field in the substitution follows, terminated by a
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CTLENDVAR byte.
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The type VSERROR is used to allow parsing bad substitutions like
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${var[7]} and generate an error when they are expanded.
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Commands in back quotes are parsed and stored in a linked list.
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The locations of these commands in the string are indicated by
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CTLBACKQ and CTLBACKQ+CTLQUOTE characters, depending upon whether
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the back quotes were enclosed in double quotes.
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Arithmetic expansion starts with CTLARI and ends with CTLENDARI.
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The character CTLESC escapes the next character, so that in case
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any of the CTL characters mentioned above appear in the input,
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they can be passed through transparently. CTLESC is also used to
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@ -153,11 +168,11 @@ right. In the case of here documents which are not subject to
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variable and command substitution, the parser doesn't insert any
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CTLESC characters to begin with (so the contents of the text
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field can be written without any processing). Other here docu-
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ments, and words which are not subject to splitting and file name
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generation, have the CTLESC characters removed during the vari-
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able and command substitution phase. Words which are subject to
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splitting and file name generation have the CTLESC characters re-
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moved as part of the file name phase.
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ments, and words which are not subject to file name generation,
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have the CTLESC characters removed during the variable and command
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substitution phase. Words which are subject to file name
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generation have the CTLESC characters removed as part of the file
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name phase.
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EXECUTION: Command execution is handled by the following files:
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eval.c The top level routines.
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@ -199,10 +214,10 @@ later.)
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The routine shellexec is the interface to the exec system call.
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EXPAND.C: Arguments are processed in three passes. The first
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(performed by the routine argstr) performs variable and command
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substitution. The second (ifsbreakup) performs word splitting
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and the third (expandmeta) performs file name generation.
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EXPAND.C: As the routine argstr generates words by parameter
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expansion, command substitution and arithmetic expansion, it
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performs word splitting on the result. As each word is output,
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the routine expandmeta performs file name generation (if enabled).
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VAR.C: Variables are stored in a hash table. Probably we should
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switch to extensible hashing. The variable name is stored in the
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@ -221,8 +236,8 @@ BUILTIN COMMANDS: The procedures for handling these are scat-
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tered throughout the code, depending on which location appears
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most appropriate. They can be recognized because their names al-
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ways end in "cmd". The mapping from names to procedures is
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specified in the file builtins, which is processed by the mkbuilt-
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ins command.
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specified in the file builtins.def, which is processed by the
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mkbuiltins command.
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A builtin command is invoked with argc and argv set up like a
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normal program. A builtin command is allowed to overwrite its
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@ -230,22 +245,20 @@ arguments. Builtin routines can call nextopt to do option pars-
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ing. This is kind of like getopt, but you don't pass argc and
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argv to it. Builtin routines can also call error. This routine
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normally terminates the shell (or returns to the main command
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loop if the shell is interactive), but when called from a builtin
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command it causes the builtin command to terminate with an exit
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status of 2.
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loop if the shell is interactive), but when called from a non-
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special builtin command it causes the builtin command to
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terminate with an exit status of 2.
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The directory bltins contains commands which can be compiled in-
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dependently but can also be built into the shell for efficiency
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reasons. The makefile in this directory compiles these programs
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in the normal fashion (so that they can be run regardless of
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whether the invoker is ash), but also creates a library named
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bltinlib.a which can be linked with ash. The header file bltin.h
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takes care of most of the differences between the ash and the
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stand-alone environment. The user should call the main routine
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"main", and #define main to be the name of the routine to use
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when the program is linked into ash. This #define should appear
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before bltin.h is included; bltin.h will #undef main if the pro-
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gram is to be compiled stand-alone.
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reasons. The header file bltin.h takes care of most of the
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differences between the ash and the stand-alone environment.
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The user should call the main routine "main", and #define main to
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be the name of the routine to use when the program is linked into
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ash. This #define should appear before bltin.h is included;
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bltin.h will #undef main if the program is to be compiled
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stand-alone. A similar approach is used for a few utilities from
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bin and usr.bin.
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CD.C: This file defines the cd and pwd builtins.
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@ -258,7 +271,7 @@ is called at appropriate points to actually handle the signal.
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When an interrupt is caught and no trap has been set for that
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signal, the routine "onint" in error.c is called.
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OUTPUT: Ash uses it's own output routines. There are three out-
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OUTPUT: Ash uses its own output routines. There are three out-
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put structures allocated. "Output" represents the standard out-
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put, "errout" the standard error, and "memout" contains output
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which is to be stored in memory. This last is used when a buil-
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@ -1222,7 +1222,7 @@ bltincmd(int argc, char **argv)
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return 127;
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}
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/*
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* Preserve exitstatus of a previous possible redirection
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* Preserve exitstatus of a previous possible command substitution
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* as POSIX mandates
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*/
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return exitstatus;
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@ -338,7 +338,7 @@ find_command(const char *name, struct cmdentry *entry, int act,
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cd = 0;
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/* If name is in the table, and not invalidated by cd, we're done */
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/* If name is in the table, we're done */
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if ((cmdp = cmdlookup(name, 0)) != NULL) {
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if (cmdp->cmdtype == CMDFUNCTION && act & DO_NOFUNC)
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cmdp = NULL;
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@ -485,8 +485,7 @@ changepath(const char *newval __unused)
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/*
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* Clear out command entries. The argument specifies the first entry in
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* PATH which has changed.
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* Clear out cached utility locations.
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*/
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void
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@ -222,9 +222,9 @@ stputs_split(const char *data, const char *syntax, int flag, char *p,
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* The result is left in the stack string.
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* When arglist is NULL, perform here document expansion.
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*
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* Caution: this function uses global state and is not reentrant.
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* However, a new invocation after an interrupted invocation is safe
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* and will reset the global state for the new call.
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* When doing something that may cause this to be re-entered, make sure
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* the stack string is empty via grabstackstr() and do not assume expdest
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* remains valid.
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*/
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void
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expandarg(union node *arg, struct arglist *arglist, int flag)
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@ -476,7 +476,7 @@ expbackq(union node *cmd, int quoted, int flag, struct worddest *dst)
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ifs = ifsset() ? ifsval() : " \t\n";
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else
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ifs = "";
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/* Don't copy trailing newlines */
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/* Remove trailing newlines */
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for (;;) {
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if (--in.nleft < 0) {
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if (in.fd < 0)
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@ -821,7 +821,7 @@ evalvar(const char *p, struct nodelist **restrict argbackq, int flag,
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/*
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* Test whether a specialized variable is set.
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* Test whether a special or positional parameter is set.
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*/
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static int
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@ -918,7 +918,7 @@ reprocess(int startloc, int flag, int subtype, int quoted,
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}
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/*
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* Add the value of a specialized variable to the stack string.
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* Add the value of a special or positional parameter to the stack string.
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*/
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static void
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@ -141,6 +141,8 @@ optschanged(void)
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/*
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* Process shell options. The global variable argptr contains a pointer
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* to the argument list; we advance it past the options.
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* If cmdline is true, process the shell's argv; otherwise, process arguments
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* to the set special builtin.
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*/
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static void
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@ -392,7 +394,7 @@ shiftcmd(int argc, char **argv)
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/*
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* The set command builtin.
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* The set builtin command.
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*/
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int
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@ -558,7 +560,7 @@ getopts(char *optstr, char *optvar, char **optfirst, char ***optnext,
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/*
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* Standard option processing (a la getopt) for builtin routines. The
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* only argument that is passed to nextopt is the option string; the
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* other arguments are unnecessary. It return the character, or '\0' on
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* other arguments are unnecessary. It returns the option, or '\0' on
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* end of input.
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*/
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