Lexical indirection operator can be changed at runtime

* xenv.l: New option -S selects the sigil to use instead of the
default '$'.
* xenv.1: Document the -S option.

2 files changed, 102 insertions, 24 deletions

diff --git a/xenv.1 b/xenv.1
index 472e240..a2dad81 100644
--- a/xenv.1
+++ b/xenv.1
@@ -13,13 +13,14 @@
 .\"
 .\" You should have received a copy of the GNU General Public License along
 .\" with xenv. If not, see <http://www.gnu.org/licenses/>.
-.TH XENV 1 "February 1, 2021" "XENV" "General Commands Manual"
+.TH XENV 1 "February 11, 2021" "XENV" "General Commands Manual"
 .SH NAME
 xenv \- expand shell variables in input files
 .SH SYNOPSIS
 \fBxenv\fR\
  [\fB\-hnrsu\fR]\
  [\fB\-D \fINAME\fR[\fB=\fIVALUE\fR]]\
+ [\fB\-S \fR[\fB$@%&#\fR]]\
  [\fB\-U \fINAME\fR]\
  [\fIFILE\fR...]
 .SH DESCRIPTION
@@ -166,6 +167,15 @@ undefined variable expands to an empty string.  This option instructs
 Naturally, this affects only \fB$\fIX\fR and \fB${\fIX\fB}\fR
 references.
 .TP
+\fB\-S \fICHAR\fR
+Changes sigil (a character that starts variable substitution) to
+\fICHAR\fR.  Allowed characters are: \fI$\fR (the default),
+.IR @ ,
+.IR % ,
+.IR & ,
+and
+.IR # .
+.TP
 .B \-s
 Generate synchronization directives, i.e. lines of the form
 \fB#line \fINUM\fR "\fIFILE\fR"\fR, which mean that the following line
diff --git a/xenv.l b/xenv.l
index 4554696..5de0b3b 100644
--- a/xenv.l
+++ b/xenv.l
@@ -31,11 +31,15 @@ int undef_error_option;     /* Treat undefined variables as error. */
 int synclines_option;       /* Generate `#line NUM "FILE"' lines. */
 int retain_unexpanded_option;/* Retain unexpanded constructs in the output. */
 int status = 0;             /* Exit status */
+int sigil = '$';
+char const sigil_chars[] = "$@%&#";
 
-static int save_state;      /* Saved scanner state. */
 static int bracecount = 0;  /* Curly brace nesting level. */
 static int emit_syncline;
 
+static void push_state(int newstate);
+static void pop_state(void);
+
 static char *findenv(char const *ident, int len);
 void expandenv(char const *ident, int len);
 
@@ -134,7 +138,7 @@ IDENT [a-zA-Z_][a-zA-Z_0-9]*
 WS [ \t][ \t]*
 OWS [ \t]*
 %s SQ DQ
-%x COMMENT FALSE	
+%x COMMENT FALSE SIGIL
 %%
 \n+  {
     ECHO;
@@ -148,11 +152,11 @@ OWS [ \t]*
  }
 \|  { expand_inline_flop(); }
 
-<DQ>\" { BEGIN(save_state); ECHO; }
-\"    { save_state = YYSTATE; BEGIN(DQ); ECHO; }
+<DQ>\" { pop_state(); ECHO; }
+\"     { push_state(DQ); ECHO; }
 
-<SQ>"'" { BEGIN(save_state); ECHO; }
-"'"   { save_state = YYSTATE; BEGIN(SQ); ECHO; }
+<SQ>"'" { pop_state(); ECHO; }
+"'"     { push_state(SQ); ECHO; }
 
 <INITIAL>^"#line ".*\n {
 	if (parse_line_directive(yytext)) {
@@ -160,13 +164,14 @@ OWS [ \t]*
 		lineno++;
 	}
  }
-<INITIAL>"${*" { save_state = YYSTATE; BEGIN(COMMENT); }
 <COMMENT>[^*\n]*        /* eat anything that's not a '*' */
 <COMMENT>"*"+[^*}\n]*   /* eat up '*'s not followed by '}'s */
 <COMMENT>\n             lineno++; /* Keep track of line numbers. */
-<COMMENT>"*"+"}"        { BEGIN(save_state); emit_syncline = 1; }
+<COMMENT>"*"+"}"        { pop_state(); emit_syncline = 1; }
 
-"$(" {
+<SIGIL>{
+"{*" { pop_state(); push_state(COMMENT); }
+"(" {
 	int nesting = 1;
 	int c;
 	while ((c = input()) != 0) {
@@ -183,22 +188,26 @@ OWS [ \t]*
 			lineno++;
 	        fputc(c, yyout);   
         }
+	pop_state();
  }
-\${IDENT} { expandenv(yytext + 1, yyleng - 1); }
-\$\{{IDENT}\} { expandenv(yytext + 2, yyleng - 3); }
-\$\{{IDENT}:?[-=?+|] {
+{IDENT} { expandenv(yytext, yyleng);
+	  pop_state(); }
+\{{IDENT}\} { expandenv(yytext + 1, yyleng - 2);
+	      pop_state(); }
+\{{IDENT}:?[-=?+|] {
 	int len;
 	char *val;
 	int test_null = 0;
 	int type = yytext[yyleng-1];
 	int suppress;
 	
-	if (yytext[yyleng-2] == ':') {
+	pop_state();
+ 	if (yytext[yyleng-2] == ':') {
 		test_null = 1;
-		len = yyleng - 4;
-	} else
 		len = yyleng - 3;
-	val = findenv(yytext + 2, len);
+	} else
+		len = yyleng - 2;
+	val = findenv(yytext + 1, len);
 	if (val && !(test_null && *val == 0)) {
 	        if (type == EXP_TERNARY || type == EXP_ALTER) {
 	                suppress = 0;
@@ -216,21 +225,35 @@ OWS [ \t]*
 	                        /* Provide default error message */
 	                        if (test_null)
 				        fprintf(stderr, "%s:%u: variable %.*s null or not set\n",
-		                                filename, lineno, len, yytext + 2);
+		                                filename, lineno, len, yytext + 1);
 			        else
 				        fprintf(stderr, "%s:%u: variable %.*s not set\n",
-		                                filename, lineno, len, yytext + 2);
+		                                filename, lineno, len, yytext + 1);
 			        YY_BREAK;
                          }
 	                 unput(c);
                 }
         }
 	bracecount++;
-	expand_inline_push(type, yytext + 2, len, suppress);
+	expand_inline_push(type, yytext + 1, len, suppress);
 }
 
-<INITIAL>{
+.   { char s[2];
+      s[0] = sigil;
+      s[1] = yytext[0];
+      echo(s, 2);
+      pop_state(); }
 
+}
+
+<INITIAL,DQ,SQ>[$@%&#]  {
+	   if (yytext[0] == sigil)		
+  	        push_state(SIGIL);
+	   else
+  	        ECHO; 	
+         }
+
+<INITIAL>{
 ^{OWS}"$$"{OWS}"unset"{WS}{IDENT}{OWS}\n {
 	int len;
 	char *ident = find_ident(yytext, &len, NULL);
@@ -389,11 +412,42 @@ expandenv(char const *ident, int len)
 				filename, lineno, len, ident);
 			status = EX_DATAERR;
 		}
-		if (retain_unexpanded_option)
+		if (retain_unexpanded_option) {
+			char c = sigil;
+			echo(&c, 1);
 			ECHO;
+		}
 	}
 }	
 
+#define MAX_STACK 1024
+
+static int state_stack[MAX_STACK];
+static int state_tos = -1;
+
+static void
+push_state(int newstate)
+{
+	if (++state_tos == MAX_STACK) {
+		fprintf(stderr, "%s:%u: out of state stack space\n",
+			filename, lineno);
+		exit(EX_SOFTWARE);
+	}
+	state_stack[state_tos] = YYSTATE;
+	BEGIN(newstate);
+}
+
+static void
+pop_state(void)
+{
+	if (state_tos == -1) {
+		fprintf(stderr, "%s:%u: out of state popup space\n",
+			filename, lineno);
+		exit(EX_SOFTWARE);
+	}
+	BEGIN(state_stack[state_tos--]);
+}
+
 struct expand_inline {
 	int type;      /* Expansion type (one of the EXP_ constants above). */
 	int suppress;  /* Suppress output. */
@@ -409,7 +463,6 @@ struct expand_inline {
 	};
 };
 
-#define MAX_STACK 1024
 static struct expand_inline expand_inline_stack[MAX_STACK];
 static int expand_inline_tos = -1;
 
@@ -684,6 +737,7 @@ usage(FILE *fp)
 	fprintf(fp, "  -U NAME          unset environment variable NAME\n");
 	fprintf(fp, "  -n               don't produce output, only report errors\n");
 	fprintf(fp, "  -r               Retain unexpanded constructs in the output\n");
+	fprintf(fp, "  -S CHAR          change sigil character (allowed chars: %s)\n", sigil_chars);
 	fprintf(fp, "  -s               generate `#line NUM \"FILE\"' lines\n");
 	fprintf(fp, "  -u               treat unset variables as errors\n");
 	fprintf(fp, "  -h               print this help text\n");
@@ -698,7 +752,7 @@ main(int argc, char **argv)
 	int dry_run = 0;
 	
 	progname = argv[0];
-	while ((c = getopt(argc, argv, "D:hnrsU:u")) != EOF) {
+	while ((c = getopt(argc, argv, "D:hnrS:sU:u")) != EOF) {
 		switch (c) {
 		case 'D':{
 			char *p = strchr(optarg, '=');
@@ -725,6 +779,20 @@ main(int argc, char **argv)
 		case 'r':
 			retain_unexpanded_option = 1;
 			break;
+
+		case 'S':
+			if (optarg[1]) {
+				fprintf(stderr, "%s: sigil too long\n",
+					progname);
+				return EX_USAGE;
+			}
+			if (!strchr(sigil_chars, optarg[0])) {
+				fprintf(stderr, "%s: %s is not allowed as a sigil; allowed characters are: %s\n",
+					progname, optarg, sigil_chars);
+				return EX_USAGE;
+			}
+			sigil = optarg[0];
+			break;
 			
 		case 's':
 			synclines_option = 1;