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sh: Improve comments in expand.c.

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This commit is contained in:
Jilles Tjoelker 2010-09-05 21:12:48 +00:00
parent 049640c1f0
commit 2ca3d70fc6
1 changed files with 37 additions and 21 deletions
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58
bin/sh/expand.c
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@ -138,12 +138,18 @@ expandhere(union node *arg, int fd)
/* /*
* Perform variable substitution and command substitution on an argument, * Perform expansions on an argument, placing the resulting list of arguments
* placing the resulting list of arguments in arglist. If EXP_FULL is true, * in arglist. Parameter expansion, command substitution and arithmetic
* perform splitting and file name expansion. When arglist is NULL, perform * expansion are always performed; additional expansions can be requested
* here document expansion. * via flag (EXP_*).
* The result is left in the stack string.
* When arglist is NULL, perform here document expansion. A partial result
* may be written to herefd, which is then not included in the stack string.
*
* Caution: this function uses global state and is not reentrant.
* However, a new invocation after an interrupted invocation is safe
* and will reset the global state for the new call.
*/ */
void void
expandarg(union node *arg, struct arglist *arglist, int flag) expandarg(union node *arg, struct arglist *arglist, int flag)
{ {
@ -195,11 +201,14 @@ expandarg(union node *arg, struct arglist *arglist, int flag)
/* /*
* Perform variable and command substitution. If EXP_FULL is set, output CTLESC * Perform parameter expansion, command substitution and arithmetic
* characters to allow for further processing. Otherwise treat * expansion, and tilde expansion if requested via EXP_TILDE/EXP_VARTILDE.
* $@ like $* since no splitting will be performed. * Processing ends at a CTLENDVAR character as well as '\0'.
* This is used to expand word in ${var+word} etc.
* If EXP_FULL, EXP_CASE or EXP_REDIR are set, keep and/or generate CTLESC
* characters to allow for further processing.
* If EXP_FULL is set, also preserve CTLQUOTEMARK characters.
*/ */
STATIC void STATIC void
argstr(char *p, int flag) argstr(char *p, int flag)
{ {
@ -212,7 +221,7 @@ argstr(char *p, int flag)
for (;;) { for (;;) {
switch (c = *p++) { switch (c = *p++) {
case '\0': case '\0':
case CTLENDVAR: /* ??? */ case CTLENDVAR:
goto breakloop; goto breakloop;
case CTLQUOTEMARK: case CTLQUOTEMARK:
/* "$@" syntax adherence hack */ /* "$@" syntax adherence hack */
@ -262,6 +271,10 @@ argstr(char *p, int flag)
breakloop:; breakloop:;
} }
/*
* Perform tilde expansion, placing the result in the stack string and
* returning the next position in the input string to process.
*/
STATIC char * STATIC char *
exptilde(char *p, int flag) exptilde(char *p, int flag)
{ {
@ -367,12 +380,11 @@ expari(int flag)
int quotes = flag & (EXP_FULL | EXP_CASE | EXP_REDIR); int quotes = flag & (EXP_FULL | EXP_CASE | EXP_REDIR);
int quoted; int quoted;
/* /*
* This routine is slightly over-complicated for * This routine is slightly over-complicated for
* efficiency. First we make sure there is * efficiency. First we make sure there is
* enough space for the result, which may be bigger * enough space for the result, which may be bigger
* than the expression if we add exponentiation. Next we * than the expression. Next we
* scan backwards looking for the start of arithmetic. If the * scan backwards looking for the start of arithmetic. If the
* next previous character is a CTLESC character, then we * next previous character is a CTLESC character, then we
* have to rescan starting from the beginning since CTLESC * have to rescan starting from the beginning since CTLESC
@ -413,9 +425,8 @@ expari(int flag)
/* /*
* Expand stuff in backwards quotes. * Perform command substitution.
*/ */
STATIC void STATIC void
expbackq(union node *cmd, int quoted, int flag) expbackq(union node *cmd, int quoted, int flag)
{ {
@ -974,6 +985,12 @@ recordregion(int start, int end, int inquotes)
* Break the argument string into pieces based upon IFS and add the * Break the argument string into pieces based upon IFS and add the
* strings to the argument list. The regions of the string to be * strings to the argument list. The regions of the string to be
* searched for IFS characters have been stored by recordregion. * searched for IFS characters have been stored by recordregion.
* CTLESC characters are preserved but have little effect in this pass
* other than escaping CTL* characters. In particular, they do not escape
* IFS characters: that should be done with the ifsregion mechanism.
* CTLQUOTEMARK characters are used to preserve empty quoted strings.
* This pass treats them as a regular character, making the string non-empty.
* Later, they are removed along with the other CTL* characters.
*/ */
STATIC void STATIC void
ifsbreakup(char *string, struct arglist *arglist) ifsbreakup(char *string, struct arglist *arglist)
@ -1075,15 +1092,14 @@ ifsbreakup(char *string, struct arglist *arglist)
} }
/*
* Expand shell metacharacters. At this point, the only control characters
* should be escapes. The results are stored in the list exparg.
*/
STATIC char expdir[PATH_MAX]; STATIC char expdir[PATH_MAX];
#define expdir_end (expdir + sizeof(expdir)) #define expdir_end (expdir + sizeof(expdir))
/*
* Perform pathname generation and remove control characters.
* At this point, the only control characters should be CTLESC and CTLQUOTEMARK.
* The results are stored in the list exparg.
*/
STATIC void STATIC void
expandmeta(struct strlist *str, int flag __unused) expandmeta(struct strlist *str, int flag __unused)
{ {
@ -1469,7 +1485,7 @@ breakloop:
/* /*
* Remove any CTLESC characters from a string. * Remove any CTLESC and CTLQUOTEMARK characters from a string.
*/ */
void void