# HG changeset patch
# User Samuel Holland <samuel@sholland.net>
# Date 1396566104 18000
# Node ID 0d295a46f853224c03aa923fd982b60b9a604558
# Parent  9a13e6637d7b87a4464166e0f8a2b3d417c74534
Here is a basic implementation of fold[0]. It does not support multibyte characters, though that would probably just require more switch cases.

diff -r 9a13e6637d7b -r 0d295a46f853 toys/pending/fold.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toys/pending/fold.c	Thu Apr 03 18:01:44 2014 -0500
@@ -0,0 +1,93 @@
+/* fold.c - fold text
+ *
+ * Copyright 2014 Samuel Holland <samuel@sholland.net>
+ *
+ * See http://pubs.opengroup.org/onlinepubs/9699919799/utilities/fold.html
+
+USE_FOLD(NEWTOY(fold, "bsw#", TOYFLAG_USR|TOYFLAG_BIN))
+
+config FOLD
+  bool "fold"
+  default n
+  help
+    usage: fold [-bs] [-w WIDTH] [FILE...]
+
+    Folds/wraps FILE or stdin at 80 columns.
+
+    -b  Wrap based on bytes instead of columns
+    -s  Wrap at farthest right whitespace
+    -w  Wrap at WIDTH columns instead of 80
+*/
+
+#define FOR_fold
+#include "toys.h"
+
+GLOBALS(
+  int w_number;
+)
+
+void do_fold(int fd, char *name)
+{
+  int buflen, i, len = 0, split;
+  int max = (toys.optflags & FLAG_w) ? TT.w_number : 80;
+  char tmp, *buf;
+
+  if (max > sizeof(toybuf)) {
+    error_exit("width (%ld) too big", max);
+  }
+
+  while (read(fd, toybuf, sizeof(toybuf))) {
+    split = -1;
+    buf = toybuf;
+    buflen = strlen(buf);
+
+    for (i = 0; i < buflen; i++) {
+      switch (buf[i]) {
+        case '\n':
+          //reset len, FLAG_b or not; just print multiple lines at once
+          len = 0;
+          continue;
+        case '\b':
+          //len cannot be negative; not allowed to wrap after backspace
+          if (toys.optflags & FLAG_b) len++;
+          else if (len > 0) len--;
+          continue;
+        case '\r':
+          //not allowed to wrap after carriage return
+          if (toys.optflags & FLAG_b) len++;
+          else len = 0;
+          continue;
+        case '\t':
+          //round to 8, but we add one after falling through
+          //(because of whitespace, but it also takes care of FLAG_b)
+          if (!(toys.optflags & FLAG_b)) len = (len & -8) + 7;
+        case ' ':
+          split = i;
+        default:
+          len++;
+      }
+
+      //we don't want to double up \n; not allowed to wrap before \b
+      if (len >= max && buf[i+1] != '\n' && buf[i+1] != '\b') {
+        if (!(toys.optflags & FLAG_s)) split = i; //we split right here
+        tmp = buf[split+1];
+        buf[split+1] = 0;
+        xprintf("%s\n", buf);
+        buf[split+1] = tmp;
+        len = 0;
+        if (split < buflen - 1) {
+          buf += split + 1;
+          i = 0;
+          buflen = strlen(buf);
+        }
+      }
+    }
+
+    xputs(buf);
+  }
+}
+
+void fold_main(void)
+{
+  loopfiles(toys.optargs, do_fold);
+}