sh: implement persistent history storage

Implement persistent history storage:
the strategy is simple at start: loads the existing .sh_history file
at exit dump it.

The implementation respects the HISTFILE variable and its POSIX
definition: ~/.sh_history is used if HISTFILE is not set.

to avoid sh to create the history file, set HISTSIZE to 0 or HISTFILE to
en empty value

Co-authored-by:	pstef
Reviewed by:	jilles
Differential Revision:	https://reviews.freebsd.org/D29493

bin/sh/histedit.c

@@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/param.h>
 #include <sys/stat.h>
 #include <dirent.h>
+#include <fcntl.h>
 #include <limits.h>
 #include <paths.h>
 #include <stdio.h>
@@ -78,6 +79,64 @@ static int comparator(const void *, const void *, void *);
 static char **sh_matches(const char *, int, int);
 static unsigned char sh_complete(EditLine *, int);
 
+static const char *
+get_histfile(void)
+{
+	const char *histfile;
+
+	/* don't try to save if the history size is 0 */
+	if (hist == NULL || histsizeval() == 0)
+		return (NULL);
+	histfile = expandstr("${HISTFILE-${HOME-}/.sh_history}");
+
+	if (histfile[0] == '\0')
+		return (NULL);
+	return (histfile);
+}
+
+void
+histsave(void)
+{
+	HistEvent he;
+	char *histtmpname = NULL;
+	const char *histfile;
+	int fd;
+	FILE *f;
+
+	if ((histfile = get_histfile()) == NULL)
+		return;
+	INTOFF;
+	asprintf(&histtmpname, "%s.XXXXXXXXXX", histfile);
+	if (histtmpname == NULL) {
+		INTON;
+		return;
+	}
+	fd = mkstemp(histtmpname);
+	if (fd == -1 || (f = fdopen(fd, "w")) == NULL) {
+		free(histtmpname);
+		INTON;
+		return;
+	}
+	if (history(hist, &he, H_SAVE_FP, f) < 1 ||
+	    rename(histtmpname, histfile) == -1)
+		unlink(histtmpname);
+	fclose(f);
+	free(histtmpname);
+	INTON;
+
+}
+
+void
+histload(void)
+{
+	const char *histfile;
+	HistEvent he;
+
+	if ((histfile = get_histfile()) == NULL)
+		return;
+	history(hist, &he, H_LOAD, histfile);
+}
+
 /*
  * Set history and editing status.  Called whenever the status may
  * have changed (figures out what to do).

bin/sh/main.c

@@ -75,6 +75,9 @@ __FBSDID("$FreeBSD$");
 #include "cd.h"
 #include "redir.h"
 #include "builtins.h"
+#ifndef NO_HISTORY
+#include "myhistedit.h"
+#endif
 
 int rootpid;
 int rootshell;
@@ -157,6 +160,10 @@ main(int argc, char *argv[])
 			read_profile(shinit);
 		}
 	}
+#ifndef NO_HISTORY
+	if (iflag)
+		histload();
+#endif
 state3:
 	state = 4;
 	popstackmark(&smark2);

bin/sh/myhistedit.h

@@ -43,4 +43,5 @@ extern int displayhist;
 void histedit(void);
 void sethistsize(const char *);
 void setterm(const char *);
-
+void histload(void);
+void histsave(void);

bin/sh/sh.1

@@ -32,7 +32,7 @@
 .\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
 .\" $FreeBSD$
 .\"
-.Dd July 6, 2020
+.Dd May 10, 2021
 .Dt SH 1
 .Os
 .Sh NAME
@@ -1351,6 +1351,15 @@ If not set, the default editor is
 The default editor used with the
 .Ic fc
 built-in.
+.It Va HISTFILE
+File used for persistent history storage.
+If unset
+.Pa ~/.sh_history
+will be used.
+If set but empty or
+.Va HISTSIZE
+is set to 0
+the shell will not load and save the history.
 .It Va HISTSIZE
 The number of previous commands that are accessible.
 .It Va HOME

bin/sh/trap.c

@@ -535,6 +535,9 @@ exitshell_savedstatus(void)
 		flushall();
 #if JOBS
 		setjobctl(0);
+#endif
+#ifndef NO_HISTORY
+		histsave();
 #endif
 	}
 	if (sig != 0 && sig != SIGSTOP && sig != SIGTSTP && sig != SIGTTIN &&