svn commit: r212243 - head/bin/sh
Jilles Tjoelker
jilles at FreeBSD.org
Sun Sep 5 21:12:48 UTC 2010
Author: jilles
Date: Sun Sep 5 21:12:48 2010
New Revision: 212243
URL: http://svn.freebsd.org/changeset/base/212243
Log:
sh: Improve comments in expand.c.
Modified:
head/bin/sh/expand.c
Modified: head/bin/sh/expand.c
==============================================================================
--- head/bin/sh/expand.c Sun Sep 5 20:13:07 2010 (r212242)
+++ head/bin/sh/expand.c Sun Sep 5 21:12:48 2010 (r212243)
@@ -138,12 +138,18 @@ expandhere(union node *arg, int fd)
/*
- * Perform variable substitution and command substitution on an argument,
- * placing the resulting list of arguments in arglist. If EXP_FULL is true,
- * perform splitting and file name expansion. When arglist is NULL, perform
- * here document expansion.
+ * Perform expansions on an argument, placing the resulting list of arguments
+ * in arglist. Parameter expansion, command substitution and arithmetic
+ * expansion are always performed; additional expansions can be requested
+ * 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
expandarg(union node *arg, struct arglist *arglist, int flag)
{
@@ -195,11 +201,14 @@ expandarg(union node *arg, struct arglis
/*
- * Perform variable and command substitution. If EXP_FULL is set, output CTLESC
- * characters to allow for further processing. Otherwise treat
- * $@ like $* since no splitting will be performed.
+ * Perform parameter expansion, command substitution and arithmetic
+ * expansion, and tilde expansion if requested via EXP_TILDE/EXP_VARTILDE.
+ * Processing ends at a CTLENDVAR character as well as '\0'.
+ * This is used to expand word in ${var+word} etc.
+ * If EXP_FULL, EXP_CASE or EXP_REDIR are set, keep and/or generate CTLESC
+ * characters to allow for further processing.
+ * If EXP_FULL is set, also preserve CTLQUOTEMARK characters.
*/
-
STATIC void
argstr(char *p, int flag)
{
@@ -212,7 +221,7 @@ argstr(char *p, int flag)
for (;;) {
switch (c = *p++) {
case '\0':
- case CTLENDVAR: /* ??? */
+ case CTLENDVAR:
goto breakloop;
case CTLQUOTEMARK:
/* "$@" syntax adherence hack */
@@ -262,6 +271,10 @@ argstr(char *p, int flag)
breakloop:;
}
+/*
+ * Perform tilde expansion, placing the result in the stack string and
+ * returning the next position in the input string to process.
+ */
STATIC char *
exptilde(char *p, int flag)
{
@@ -367,12 +380,11 @@ expari(int flag)
int quotes = flag & (EXP_FULL | EXP_CASE | EXP_REDIR);
int quoted;
-
/*
* This routine is slightly over-complicated for
* efficiency. First we make sure there is
* 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
* next previous character is a CTLESC character, then we
* 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
expbackq(union node *cmd, int quoted, int flag)
{
@@ -974,6 +985,12 @@ recordregion(int start, int end, int inq
* Break the argument string into pieces based upon IFS and add the
* strings to the argument list. The regions of the string to be
* 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
ifsbreakup(char *string, struct arglist *arglist)
@@ -1075,15 +1092,14 @@ ifsbreakup(char *string, struct 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];
#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
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
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