add -i flag to sed to do in-place editing; mostly based on freebsd

feedback/ok deraadt@ millert@

5 files changed, 276 insertions, 108 deletions

diff --git a/usr.bin/sed/defs.h b/usr.bin/sed/defs.h
index 8694f181ad8..eaea6b5564e 100644
--- a/usr.bin/sed/defs.h
+++ b/usr.bin/sed/defs.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: defs.h,v 1.5 2015/01/19 15:30:52 krw Exp $ */
+/*	$OpenBSD: defs.h,v 1.6 2015/07/17 20:38:57 jasper Exp $ */
 /*-
  * Copyright (c) 1992 Diomidis Spinellis.
  * Copyright (c) 1992, 1993
@@ -128,6 +128,7 @@ typedef struct {
 	char *space;		/* Current space pointer. */
 	size_t len;		/* Current length. */
 	int deleted;		/* If deleted. */
+	int append_newline;	/* If originally terminated by \n. */
 	char *back;		/* Backing memory. */
 	size_t blen;		/* Backing memory length. */
 } SPACE;
diff --git a/usr.bin/sed/extern.h b/usr.bin/sed/extern.h
index 6d2c0324cfd..16b58ac94e1 100644
--- a/usr.bin/sed/extern.h
+++ b/usr.bin/sed/extern.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: extern.h,v 1.9 2015/04/13 05:11:23 deraadt Exp $ */
+/*	$OpenBSD: extern.h,v 1.10 2015/07/17 20:38:57 jasper Exp $ */
 /*-
  * Copyright (c) 1992 Diomidis Spinellis.
  * Copyright (c) 1992, 1993
@@ -40,17 +40,19 @@ extern regmatch_t *match;
 extern size_t maxnsub;
 extern u_long linenum;
 extern size_t appendnum;
-extern int lastline;
 extern int Eflag, aflag, eflag, nflag;
-extern char *fname;
+extern const char *fname, *outfname;
+extern FILE *infile, *outfile;
 
 void	 cfclose(struct s_command *, struct s_command *);
 void	 compile(void);
-void	 cspace(SPACE *, char *, size_t, enum e_spflag);
+void	 cspace(SPACE *, const char *, size_t, enum e_spflag);
 char	*cu_fgets(char **, size_t *);
 void	 err(int, const char *, ...);
 int	 mf_fgets(SPACE *, enum e_spflag);
+int	 lastline(void);
 void	 process(void);
+void	 resetranges(void);
 char	*strregerror(int, regex_t *);
 void	*xmalloc(size_t);
 void	*xreallocarray(void *, size_t, size_t);
diff --git a/usr.bin/sed/main.c b/usr.bin/sed/main.c
index d7cc3743161..19892d34915 100644
--- a/usr.bin/sed/main.c
+++ b/usr.bin/sed/main.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: main.c,v 1.18 2014/11/26 18:34:51 millert Exp $	*/
+/*	$OpenBSD: main.c,v 1.19 2015/07/17 20:38:57 jasper Exp $	*/
 
 /*-
  * Copyright (c) 1992 Diomidis Spinellis.
@@ -34,6 +34,7 @@
  */
 
 #include <sys/types.h>
+#include <sys/stat.h>
 
 #include <ctype.h>
 #include <errno.h>
@@ -45,6 +46,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <libgen.h>
 
 #include "defs.h"
 #include "extern.h"
@@ -78,15 +80,23 @@ struct s_flist {
  */
 static struct s_flist *files, **fl_nextp = &files;
 
+FILE *infile;			/* Current input file */
+FILE *outfile;			/* Current output file */
+
 int Eflag, aflag, eflag, nflag;
+static int rval;	/* Exit status */
 
 /*
  * Current file and line number; line numbers restart across compilation
- * units, but span across input files.
+ * units, but span across input files.  The latter is optional if editing
+ * in place.
  */
-char *fname;			/* File name. */
+const char *fname;		/* File name. */
+const char *outfname;		/* Output file name */
+static char oldfname[PATH_MAX];	/* Old file name (for in-place editing) */
+static char tmpfname[PATH_MAX];	/* Temporary file name (for in-place editing) */
+char *inplace;			/* Inplace edit file extension */
 u_long linenum;
-int lastline;			/* TRUE on the last line of the last file */
 
 static void add_compunit(enum e_cut, char *);
 static void add_file(char *);
@@ -97,7 +107,8 @@ main(int argc, char *argv[])
 	int c, fflag;
 
 	fflag = 0;
-	while ((c = getopt(argc, argv, "Eae:f:nru")) != -1)
+	inplace = NULL;
+	while ((c = getopt(argc, argv, "Eae:f:i::nru")) != -1)
 		switch (c) {
 		case 'E':
 		case 'r':
@@ -114,6 +125,9 @@ main(int argc, char *argv[])
 			fflag = 1;
 			add_compunit(CU_FILE, optarg);
 			break;
+		case 'i':
+			inplace = optarg ? optarg : "";
+			break;
 		case 'n':
 			nflag = 1;
 			break;
@@ -123,8 +137,8 @@ main(int argc, char *argv[])
 		default:
 		case '?':
 			(void)fprintf(stderr,
-			    "usage: sed [-aEnru] command [file ...]\n"
-			    "       sed [-aEnru] [-e command] [-f command_file] [file ...]\n");
+			    "usage: sed [-aEnru] [-i [extension]] command [file ...]\n"
+			    "       sed [-aEnru] [-i [extension]] [-e command] [-f command_file] [file ...]\n");
 			exit(1);
 		}
 	argc -= optind;
@@ -148,7 +162,7 @@ main(int argc, char *argv[])
 	cfclose(prog, NULL);
 	if (fclose(stdout))
 		err(FATAL, "stdout: %s", strerror(errno));
-	exit (0);
+	exit (rval);
 }
 
 /*
@@ -258,69 +272,128 @@ again:
 int
 mf_fgets(SPACE *sp, enum e_spflag spflag)
 {
-	static FILE *f;		/* Current open file */
+	struct stat sb;
 	size_t len;
 	char *p;
-	int c;
+	int c, fd;
+	static int firstfile;
 
-	if (f == NULL)
-		/* Advance to first non-empty file */
-		for (;;) {
-			if (files == NULL) {
-				lastline = 1;
-				return (0);
-			}
-			if (files->fname == NULL) {
-				f = stdin;
-				fname = "stdin";
-			} else {
-				fname = files->fname;
-				if ((f = fopen(fname, "r")) == NULL)
-					err(FATAL, "%s: %s",
-					    fname, strerror(errno));
+	if (infile == NULL) {
+		/* stdin? */
+		if (files->fname == NULL) {
+			if (inplace != NULL)
+				err(FATAL, "-i may not be used with stdin");
+			infile = stdin;
+			fname = "stdin";
+			outfile = stdout;
+			outfname = "stdout";
+		}
+
+		firstfile = 1;
+	}
+
+	for (;;) {
+		if (infile != NULL && (c = getc(infile)) != EOF) {
+			(void)ungetc(c, infile);
+			break;
+		}
+		/* If we are here then either eof or no files are open yet */
+		if (infile == stdin) {
+			sp->len = 0;
+			return (0);
+		}
+		if (infile != NULL) {
+			fclose(infile);
+			if (*oldfname != '\0') {
+				if (rename(fname, oldfname) != 0) {
+					err(WARNING, "rename()");
+					unlink(tmpfname);
+					exit(1);
+				}
+				*oldfname = '\0';
 			}
-			if ((c = getc(f)) != EOF) {
-				(void)ungetc(c, f);
-				break;
+			if (*tmpfname != '\0') {
+				if (outfile != NULL && outfile != stdout)
+					fclose(outfile);
+				outfile = NULL;
+				rename(tmpfname, fname);
+				*tmpfname = '\0';
 			}
-			(void)fclose(f);
+			outfname = NULL;
+		}
+		if (firstfile == 0)
 			files = files->next;
+		else
+			firstfile = 0;
+		if (files == NULL) {
+			sp->len = 0;
+			return (0);
+		}
+		fname = files->fname;
+		if (inplace != NULL) {
+			if (lstat(fname, &sb) != 0)
+				err(1, "%s", fname);
+			if (!S_ISREG(sb.st_mode))
+				err(FATAL, "%s: %s %s", fname,
+				    "in-place editing only",
+				    "works for regular files");
+			if (*inplace != '\0') {
+				strlcpy(oldfname, fname,
+				    sizeof(oldfname));
+				len = strlcat(oldfname, inplace,
+				    sizeof(oldfname));
+				if (len > sizeof(oldfname))
+					err(FATAL, "%s: name too long", fname);
+			}
+			len = snprintf(tmpfname, sizeof(tmpfname), "%s/sedXXXXXXXXXX",
+			    dirname(fname));
+			if (len >= sizeof(tmpfname))
+				err(FATAL, "%s: name too long", fname);
+			if ((fd = mkstemp(tmpfname)) == -1)
+				err(FATAL, "%s", fname);
+			if ((outfile = fdopen(fd, "w")) == NULL) {
+				unlink(tmpfname);
+				err(FATAL, "%s", fname);
+			}
+			fchown(fileno(outfile), sb.st_uid, sb.st_gid);
+			fchmod(fileno(outfile), sb.st_mode & ALLPERMS);
+			outfname = tmpfname;
+			linenum = 0;
+			resetranges();
+		} else {
+			outfile = stdout;
+			outfname = "stdout";
+		}
+		if ((infile = fopen(fname, "r")) == NULL) {
+			err(WARNING, "%s", fname);
+			rval = 1;
+			continue;
 		}
-
-	if (lastline) {
-		sp->len = 0;
-		return (0);
 	}
 
 	/*
+	 * We are here only when infile is open and we still have something
+	 * to read from it.
+	 *
 	 * Use fgetln so that we can handle essentially infinite input data.
 	 * Can't use the pointer into the stdio buffer as the process space
 	 * because the ungetc() can cause it to move.
 	 */
-	p = fgetln(f, &len);
-	if (ferror(f))
+	p = fgetln(infile, &len);
+	if (ferror(infile))
 		err(FATAL, "%s: %s", fname, strerror(errno ? errno : EIO));
+	if (len != 0 && p[len - 1] == '\n') {
+		sp->append_newline = 1;
+		len--;
+	} else if (!lastline()) {
+		sp->append_newline = 1;
+	} else {
+		sp->append_newline = 0;
+	}
 	cspace(sp, p, len, spflag);
 
 	linenum++;
-	/* Advance to next non-empty file */
-	while ((c = getc(f)) == EOF) {
-		(void)fclose(f);
-		files = files->next;
-		if (files == NULL) {
-			lastline = 1;
-			return (1);
-		}
-		if (files->fname == NULL) {
-			f = stdin;
-			fname = "stdin";
-		} else {
-			fname = files->fname;
-			if ((f = fopen(fname, "r")) == NULL)
-				err(FATAL, "%s: %s", fname, strerror(errno));
-		}
-	}
-	(void)ungetc(c, f);
+
 	return (1);
 }
 
@@ -354,3 +427,51 @@ add_file(char *s)
 	fp->fname = s;
 	fl_nextp = &fp->next;
 }
+
+
+static int
+next_files_have_lines()
+{
+       struct s_flist *file;
+       FILE *file_fd;
+       int ch;
+
+       file = files;
+       while ((file = file->next) != NULL) {
+	       if ((file_fd = fopen(file->fname, "r")) == NULL)
+		       continue;
+
+	       if ((ch = getc(file_fd)) != EOF) {
+		       /*
+			* This next file has content, therefore current
+			* file doesn't contains the last line.
+			*/
+		       ungetc(ch, file_fd);
+		       fclose(file_fd);
+		       return (1);
+	       }
+
+	       fclose(file_fd);
+       }
+
+       return (0);
+}
+
+int
+lastline(void)
+{
+	int ch;
+
+	if (feof(infile)) {
+		return !(
+		    (inplace == NULL) &&
+		    next_files_have_lines());
+	}
+	if ((ch = getc(infile)) == EOF) {
+		return !(
+		    (inplace == NULL) &&
+		    next_files_have_lines());
+	}
+	ungetc(ch, infile);
+	return (0);
+}
diff --git a/usr.bin/sed/process.c b/usr.bin/sed/process.c
index aa7ea51d0c4..d61249e0a26 100644
--- a/usr.bin/sed/process.c
+++ b/usr.bin/sed/process.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: process.c,v 1.23 2015/04/18 18:28:37 deraadt Exp $	*/
+/*	$OpenBSD: process.c,v 1.24 2015/07/17 20:38:57 jasper Exp $	*/
 
 /*-
  * Copyright (c) 1992 Diomidis Spinellis.
@@ -55,6 +55,7 @@ static SPACE HS, PS, SS;
 #define	pd		PS.deleted
 #define	ps		PS.space
 #define	psl		PS.len
+#define	psanl		PS.append_newline
 #define	hs		HS.space
 #define	hsl		HS.len
 
@@ -76,7 +77,10 @@ static regex_t *defpreg;
 size_t maxnsub;
 regmatch_t *match;
 
-#define OUT(s) do { fwrite(s, sizeof(u_char), psl, stdout); } while (0)
+#define OUT() do {\
+	fwrite(ps, 1, psl, outfile);\
+	if (psanl) fputc('\n', outfile);\
+} while (0)
 
 void
 process(void)
@@ -85,6 +89,7 @@ process(void)
 	SPACE tspace;
 	size_t len, oldpsl;
 	char *p;
+	int oldpsanl;
 
 	for (linenum = 0; mf_fgets(&PS, REPLACE);) {
 		pd = 0;
@@ -118,8 +123,8 @@ redirect:
 			case 'c':
 				pd = 1;
 				psl = 0;
-				if (cp->a2 == NULL || lastaddr)
-					(void)printf("%s", cp->t);
+				if (cp->a2 == NULL || lastaddr || lastline())
+					(void)fprintf(outfile, "%s", cp->t);
 				break;
 			case 'd':
 				pd = 1;
@@ -128,7 +133,7 @@ redirect:
 				if (pd)
 					goto new;
 				if (psl == 0 ||
-				    (p = memchr(ps, '\n', psl - 1)) == NULL) {
+				    (p = memchr(ps, '\n', psl)) == NULL) {
 					pd = 1;
 					goto new;
 				} else {
@@ -140,25 +145,25 @@ redirect:
 				cspace(&PS, hs, hsl, REPLACE);
 				break;
 			case 'G':
-				if (hs == NULL)
-					cspace(&HS, "\n", 1, REPLACE);
+				cspace(&PS, "\n", 1, 0);
 				cspace(&PS, hs, hsl, 0);
 				break;
 			case 'h':
 				cspace(&HS, ps, psl, REPLACE);
 				break;
 			case 'H':
+				cspace(&HS, "\n", 1, 0);
 				cspace(&HS, ps, psl, 0);
 				break;
 			case 'i':
-				(void)printf("%s", cp->t);
+				(void)fprintf(outfile, "%s", cp->t);
 				break;
 			case 'l':
 				lputs(ps);
 				break;
 			case 'n':
 				if (!nflag && !pd)
-					OUT(ps);
+					OUT();
 				flush_appends();
 				if (!mf_fgets(&PS, REPLACE))
 					exit(0);
@@ -166,33 +171,32 @@ redirect:
 				break;
 			case 'N':
 				flush_appends();
-				if (!mf_fgets(&PS, 0)) {
-					if (!nflag && !pd)
-						OUT(ps);
+				cspace(&PS, "\n", 1, 0);
+				if (!mf_fgets(&PS, 0))
 					exit(0);
-				}
 				break;
 			case 'p':
 				if (pd)
 					break;
-				OUT(ps);
+				OUT();
 				break;
 			case 'P':
 				if (pd)
 					break;
-				if (psl != 0 &&
-				    (p = memchr(ps, '\n', psl - 1)) != NULL) {
+				if ((p = memchr(ps, '\n', psl)) != NULL) {
 					oldpsl = psl;
-					psl = (p + 1) - ps;
-					OUT(ps);
+					oldpsanl = psanl;
+					psl = p - ps;
+					psanl = 1;
+					OUT();
 					psl = oldpsl;
 				} else {
-					OUT(ps);
+					OUT();
 				}
 				break;
 			case 'q':
 				if (!nflag && !pd)
-					OUT(ps);
+					OUT();
 				flush_appends();
 				exit(0);
 			case 'r':
@@ -225,34 +229,36 @@ redirect:
 				    DEFFILEMODE)) == -1)
 					err(FATAL, "%s: %s",
 					    cp->t, strerror(errno));
-				if (write(cp->u.fd, ps, psl) != psl)
+				if (write(cp->u.fd, ps, psl) != psl ||
+				    write(cp->u.fd, "\n", 1) != 1)
 					err(FATAL, "%s: %s",
 					    cp->t, strerror(errno));
 				break;
 			case 'x':
 				if (hs == NULL)
-					cspace(&HS, "\n", 1, REPLACE);
+					cspace(&HS, "", 0, REPLACE);
 				tspace = PS;
 				PS = HS;
+				psanl = tspace.append_newline;
 				HS = tspace;
 				break;
 			case 'y':
 				if (pd || psl == 0)
 					break;
-				for (p = ps, len = psl; --len; ++p)
+				for (p = ps, len = psl; len--; ++p)
 					*p = cp->u.y[(unsigned char)*p];
 				break;
 			case ':':
 			case '}':
 				break;
 			case '=':
-				(void)printf("%lu\n", linenum);
+				(void)fprintf(outfile, "%lu\n", linenum);
 			}
 			cp = cp->next;
 		} /* for all cp */
 
 new:		if (!nflag && !pd)
-			OUT(ps);
+			OUT();
 		flush_appends();
 	} /* for all lines */
 }
@@ -263,7 +269,7 @@ new:		if (!nflag && !pd)
  */
 #define	MATCH(a)						\
 	(a)->type == AT_RE ? regexec_e((a)->u.r, ps, 0, 1, psl) :	\
-	    (a)->type == AT_LINE ? linenum == (a)->u.l : lastline
+	    (a)->type == AT_LINE ? linenum == (a)->u.l : lastline()
 
 /*
  * Return TRUE if the command applies to the current line.  Sets the inrange
@@ -305,6 +311,19 @@ applies(struct s_command *cp)
 }
 
 /*
+ * Reset all inrange markers.
+ */
+void
+resetranges(void)
+{
+	struct s_command *cp;
+
+	for (cp = prog; cp; cp = cp->code == '{' ? cp->u.c : cp->next)
+		if (cp->a2)
+			cp->inrange = 0;
+}
+
+/*
  * substitute --
  *	Do substitutions in the pattern space.  Currently, we build a
  *	copy of the new pattern space in the substitute space structure
@@ -392,19 +411,21 @@ substitute(struct s_command *cp)
 	 */
 	tspace = PS;
 	PS = SS;
+	psanl = tspace.append_newline;
 	SS = tspace;
 	SS.space = SS.back;
 
 	/* Handle the 'p' flag. */
 	if (cp->u.s->p)
-		OUT(ps);
+		OUT();
 
 	/* Handle the 'w' flag. */
 	if (cp->u.s->wfile && !pd) {
 		if (cp->u.s->wfd == -1 && (cp->u.s->wfd = open(cp->u.s->wfile,
 		    O_WRONLY|O_APPEND|O_CREAT|O_TRUNC, DEFFILEMODE)) == -1)
 			err(FATAL, "%s: %s", cp->u.s->wfile, strerror(errno));
-		if (write(cp->u.s->wfd, ps, psl) != psl)
+		if (write(cp->u.s->wfd, ps, psl) != psl ||
+		    write(cp->u.s->wfd, "\n", 1) != 1)
 			err(FATAL, "%s: %s", cp->u.s->wfile, strerror(errno));
 	}
 	return (1);
@@ -425,7 +446,7 @@ flush_appends(void)
 		switch (appends[i].type) {
 		case AP_STRING:
 			fwrite(appends[i].s, sizeof(char), appends[i].len, 
-			    stdout);
+			    outfile);
 			break;
 		case AP_FILE:
 			/*
@@ -439,12 +460,12 @@ flush_appends(void)
 			if ((f = fopen(appends[i].s, "r")) == NULL)
 				break;
 			while ((count = fread(buf, sizeof(char), sizeof(buf), f)))
-				(void)fwrite(buf, sizeof(char), count, stdout);
+				(void)fwrite(buf, sizeof(char), count, outfile);
 			(void)fclose(f);
 			break;
 		}
-	if (ferror(stdout))
-		err(FATAL, "stdout: %s", strerror(errno ? errno : EIO));
+	if (ferror(outfile))
+		err(FATAL, "%s: %s", outfname, strerror(errno ? errno : EIO));
 	appendx = sdone = 0;
 }
 
@@ -452,10 +473,14 @@ static void
 lputs(char *s)
 {
 	int count;
-	char *escapes, *p;
+	const char *escapes;
+	char *p;
 	struct winsize win;
 	static int termwidth = -1;
 
+	if (outfile != stdout)
+		termwidth = 60;
+
 	if (termwidth == -1) {
 		termwidth = 0;
 		if ((p = getenv("COLUMNS")))
@@ -470,29 +495,33 @@ lputs(char *s)
 
 	for (count = 0; *s; ++s) { 
 		if (count >= termwidth) {
-			(void)printf("\\\n");
+			(void)fprintf(outfile, "\\\n");
 			count = 0;
 		}
 		if (isascii((unsigned char)*s) && isprint((unsigned char)*s)
 		    && *s != '\\') {
-			(void)putchar(*s);
+			(void)fputc(*s, outfile);
 			count++;
-		} else if (*s != '\n') {
+		} else if (*s == '\n') {
+			(void)fputc('$', outfile);
+			(void)fputc('\n', outfile);
+			count = 0;
+		} else {
 			escapes = "\\\a\b\f\r\t\v";
-			(void)putchar('\\');
+			(void)fputc('\\', outfile);
 			if ((p = strchr(escapes, *s))) {
-				(void)putchar("\\abfrtv"[p - escapes]);
+				(void)fputc("\\abfrtv"[p - escapes], outfile);
 				count += 2;
 			} else {
-				(void)printf("%03o", *(u_char *)s);
+				(void)fprintf(outfile, "%03o", *(u_char *)s);
 				count += 4;
 			}
 		}
 	}
-	(void)putchar('$');
-	(void)putchar('\n');
-	if (ferror(stdout))
-		err(FATAL, "stdout: %s", strerror(errno ? errno : EIO));
+	(void)fputc('$', outfile);
+	(void)fputc('\n', outfile);
+	if (ferror(outfile))
+		err(FATAL, "%s: %s", outfname, strerror(errno ? errno : EIO));
 }
 
 static inline int
@@ -507,9 +536,7 @@ regexec_e(regex_t *preg, const char *string, int eflags,
 	} else
 		defpreg = preg;
 
-	/* Set anchors, discounting trailing newline (if any). */
-	if (slen > 0 && string[slen - 1] == '\n')
-		slen--;
+	/* Set anchors */
 	match[0].rm_so = 0;
 	match[0].rm_eo = slen;
 	
@@ -575,7 +602,7 @@ regsub(SPACE *sp, char *string, char *src)
  *	space as necessary.
  */
 void
-cspace(SPACE *sp, char *p, size_t len, enum e_spflag spflag)
+cspace(SPACE *sp, const char *p, size_t len, enum e_spflag spflag)
 {
 	size_t tlen;
 
diff --git a/usr.bin/sed/sed.1 b/usr.bin/sed/sed.1
index 91f235d981e..a5307bef7d2 100644
--- a/usr.bin/sed/sed.1
+++ b/usr.bin/sed/sed.1
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: sed.1,v 1.44 2014/10/22 23:23:22 schwarze Exp $
+.\"	$OpenBSD: sed.1,v 1.45 2015/07/17 20:38:57 jasper Exp $
 .\"
 .\" Copyright (c) 1992, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -32,7 +32,7 @@
 .\"
 .\"	from: @(#)sed.1	8.2 (Berkeley) 12/30/93
 .\"
-.Dd $Mdocdate: October 22 2014 $
+.Dd $Mdocdate: July 17 2015 $
 .Dt SED 1
 .Os
 .Sh NAME
@@ -47,6 +47,7 @@
 .Op Fl aEnru
 .Op Fl e Ar command
 .Op Fl f Ar command_file
+.Op Fl i Ns Op Ar extension
 .Op Ar
 .Sh DESCRIPTION
 The
@@ -94,6 +95,16 @@ Append the editing commands found in the file
 .Ar command_file
 to the list of commands.
 The editing commands should each be listed on a separate line.
+.It Fl i Ar extension
+Edit files in-place, saving backups with the specified
+.Ar extension .
+If a zero-length
+.Ar extension
+is given, no backup will be saved.
+It is not recommended to give a zero-length
+.Ar extension
+when in-place editing files, as you risk corruption or partial content
+in situations where disk space is exhausted, etc.
 .It Fl r
 An alias for
 .Fl E ,
@@ -510,6 +521,12 @@ command,
 squeezing excess empty lines from standard input:
 .Bd -literal -offset indent
 $ sed -n '
+.Pp
+The
+.Fl i
+option is a non-standard
+.Fx
+extension and may not be available on other operating systems.
 # Write non-empty lines.
 /./ {
     p
@@ -543,7 +560,7 @@ utility is compliant with the
 specification.
 .Pp
 The flags
-.Op Fl aEru
+.Op Fl aEiru
 are extensions to that specification.
 .Pp
 The use of newlines to separate multiple commands on the command line