awk: fix backslash handling in sub() builtins

function                                             old     new   delta
awk_sub                                              559     544     -15

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 66 insertions, 22 deletions

diff --git a/editors/awk.c b/editors/awk.c
index 0f062dcdb..f77573806 100644
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -2492,7 +2492,7 @@ static char *awk_printf(node *n, size_t *len)
  * store result into (dest), return number of substitutions.
  * If nm = 0, replace all matches.
  * If src or dst is NULL, use $0.
- * If subexp != 0, enable subexpression matching (\1-\9).
+ * If subexp != 0, enable subexpression matching (\0-\9).
  */
 static int awk_sub(node *rn, const char *repl, int nm, var *src, var *dest, int subexp)
 {
@@ -2520,35 +2520,32 @@ static int awk_sub(node *rn, const char *repl, int nm, var *src, var *dest, int
                 residx += eo;
                 if (++match_no >= nm) {
                         const char *s;
-                        int nbs;
+                        int bslash;
 
                         /* replace */
                         residx -= (eo - so);
-                        nbs = 0;
+                        bslash = 0;
                         for (s = repl; *s; s++) {
-                                char c = resbuf[residx++] = *s;
-                                if (c == '\\') {
-                                        nbs++;
-                                        continue;
+                                char c = *s;
+                                if (c == '\\' && s[1]) {
+                                        bslash ^= 1;
+                                        if (bslash)
+                                                continue;
                                 }
-                                if (c == '&' || (subexp && c >= '0' && c <= '9')) {
-                                        int j;
-                                        residx -= ((nbs + 3) >> 1);
-                                        j = 0;
+                                if ((!bslash && c == '&')
+                                 || (subexp && bslash && c >= '0' && c <= '9')
+                                ) {
+                                        int n, j = 0;
                                         if (c != '&') {
                                                 j = c - '0';
-                                                nbs++;
                                         }
-                                        if (nbs % 2) {
-                                                resbuf[residx++] = c;
-                                        } else {
-                                                int n = pmatch[j].rm_eo - pmatch[j].rm_so;
-                                                resbuf = qrealloc(resbuf, residx + replen + n, &resbufsize);
-                                                memcpy(resbuf + residx, sp + pmatch[j].rm_so, n);
-                                                residx += n;
-                                        }
-                                }
-                                nbs = 0;
+                                        n = pmatch[j].rm_eo - pmatch[j].rm_so;
+                                        resbuf = qrealloc(resbuf, residx + replen + n, &resbufsize);
+                                        memcpy(resbuf + residx, sp + pmatch[j].rm_so, n);
+                                        residx += n;
+                                } else
+                                        resbuf[residx++] = c;
+                                bslash = 0;
                         }
                 }
 
diff --git a/testsuite/awk.tests b/testsuite/awk.tests
index cdab93d21..c61d32947 100755
--- a/testsuite/awk.tests
+++ b/testsuite/awk.tests
@@ -552,4 +552,51 @@ testing "awk = has higher precedence than == (despite what gawk manpage claims)"
         '0\n1\n2\n1\n3\n' \
         '' ''
 
+sq="'"
+testing 'awk gensub backslashes \' \
+        'awk '$sq'BEGIN { s="\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\
+\\|\\
+' \
+        '' ''
+testing 'awk gensub backslashes \\' \
+        'awk '$sq'BEGIN { s="\\\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\\\
+\\|\\
+' \
+        '' ''
+# gawk 5.1.1 handles trailing unpaired \ inconsistently.
+# If replace string is single \, it is used verbatim,
+# but if it is \\\ (three slashes), gawk uses "\<NUL>" (!!!), not "\\" as you would expect.
+testing 'awk gensub backslashes \\\' \
+        'awk '$sq'BEGIN { s="\\\\\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\\\\\
+\\\\|\\\\
+' \
+        '' ''
+testing 'awk gensub backslashes \\\\' \
+        'awk '$sq'BEGIN { s="\\\\\\\\"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\\\\\\\
+\\\\|\\\\
+' \
+        '' ''
+testing 'awk gensub backslashes \&' \
+        'awk '$sq'BEGIN { s="\\&"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\&
+&|&
+' \
+        '' ''
+testing 'awk gensub backslashes \0' \
+        'awk '$sq'BEGIN { s="\\0"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\0
+a|a
+' \
+        '' ''
+testing 'awk gensub backslashes \\0' \
+        'awk '$sq'BEGIN { s="\\\\0"; print "s=" s; print gensub("a", s, "g", "a|a") }'$sq \
+        's=\\\\0
+\\0|\\0
+' \
+        '' ''
+
 exit $FAILCOUNT