trap: Implement POSIX.1-2008 trap reset behaviour (#2)

Clarifies a couple of issues with the previous patch, and expands on the rationale in the commit message. Sorry for the noise -- jperkin

POSIX.1-2008 for trap adds the following behaviour:

If the first operand is an unsigned decimal integer, the shell shall treat all operands as conditions, and shall reset each condition to the default value.

The interpretation of this behaviour differs among other shells. In the case where the first operand is an invalid signo:

bash-4.3.39(1), zsh-5.1.1:

    $ trap echo 1 2 3
    $ trap 100 1 2
    $ trap
    trap -- '100' SIGHUP
    trap -- '100' SIGINT
    trap -- 'echo' SIGQUIT

mksh-51:

    $ trap echo 1 2 3
    $ trap 100 1 2
    mksh: trap: bad signal '100'
    $ trap
    trap -- echo QUIT

ksh 93u+:

    $ trap echo 1 2 3
    $ trap 100 1 2
    ksh: trap: 100: bad trap
    $ trap
    trap -- echo QUIT
    trap -- echo INT
    trap -- echo HUP

As the standard does not appear to specify that the first operand must be a valid signo for this behaviour to be triggered, we align with the ksh behaviour:

    $ trap echo 1 2 3
    $ trap 100 1 2
    trap: 100: bad trap
    $ trap
    trap -- 'echo' HUP
    trap -- 'echo' INT
    trap -- 'echo' QUIT

As for the case of the first operand being a signal name:

bash-4.3.39(1), mksh-51, ksh 93u+:

    $ trap echo 1 2 3
    $ trap HUP 2
    $ trap
    trap -- 'echo' SIGHUP
    trap -- 'HUP' SIGINT
    trap -- 'echo' SIGQUIT

zsh-5.1.1:

    $ trap echo 1 2 3
    $ trap HUP 2
    $ trap
    trap -- echo QUIT

Here we go with the majority and a strict interpretation of the standard, parsing it as a string rather than a signal:

    $ trap echo 1 2 3
    $ trap HUP 2
    $ trap
    trap -- 'echo' HUP
    trap -- 'HUP' INT
    trap -- 'echo' QUIT
---
 src/trap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 82d4263..3dc1949 100644
@@ -112,7 +112,7 @@ trapcmd(int argc, char **argv)
 		}
 		return 0;
 	}
-	if (!ap[1])
+	if ((!ap[1]) || (is_number(*ap)))
 		action = NULL;
 	else
 		action = *ap++;

2.4.9 (Apple Git-60)

-- 
Jonathan Perkin  -  Joyent, Inc.  -  www.joyent.com

So dash's behaviour is the same as bash. I'm not changing this.

Cheers,

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Ok, that's fair enough. New patch below which supports the new behaviour but matches bash for all cases, as well as retaining historical dash behaviour for invalid signos.

1. First operand an integer but invalid signo:

    bash-4.3.39(1), dash (without patch), dash (with patch)

      $ trap 100 1 2; trap
      trap -- '100' HUP
      trap -- '100' INT

2. First operand not an integer but valid signame:

bash-4.3.39(1), dash (without patch), dash (with patch)

$ trap HUP 2; trap
trap -- '100' HUP
trap -- 'HUP' INT

3. First operand an integer and valid signo:

dash (without patch)

$ trap 1 2; trap
trap -- '100' HUP
trap -- '1' INT

bash-4.3.39(1), dash (with patch)

$ trap 1 2; trap
[no output]

Hopefully that's acceptable. I've inlined most of the format-patch below, I didn't know if attachments are welcome to this list.

Cheers,

Subject: [PATCH] trap: Implement POSIX.1-2008 trap reset behaviour

POSIX.1-2008 for trap adds the following behaviour:

    If the first operand is an unsigned decimal integer, the shell shall
    treat all operands as conditions, and shall reset each condition to
    the default value.

Historically dash has treated the first operand as an action.  In order
not to change this behaviour, only valid signal numbers will trigger the
additional clause.  This matches the behaviour of bash in this regard.
---
 src/jobs.c | 4 ++--
 src/trap.c | 9 +++++----
 src/trap.h | 2 +-
 3 files changed, 8 insertions(+), 7 deletions(-)

index c2c2332..0b1ae79 100644
@@ -259,7 +259,7 @@ usage:
 	}
 
 	if (**++argv == '-') {
-		signo = decode_signal(*argv + 1, 1);
+		signo = decode_signal(*argv + 1, 1, 0);
 		if (signo < 0) {
 			int c;
 

@@ -273,7 +273,7 @@ usage:
 					list = 1;
 					break;
 				case 's':
-					signo = decode_signal(optionarg, 1);
+					signo = decode_signal(optionarg, 1, 0);
 					if (signo < 0) {
 						sh_error(
 							"invalid signal number or name: %s",

index 82d4263..f2988bc 100644
@@ -112,12 +112,12 @@ trapcmd(int argc, char **argv)
 		}
 		return 0;
 	}
-	if (!ap[1])
+	if ((!ap[1]) || (decode_signal(*ap, 0, 1)) >= 0)
 		action = NULL;
 	else
 		action = *ap++;
 	while (*ap) {
-		if ((signo = decode_signal(*ap, 0)) < 0) {
+		if ((signo = decode_signal(*ap, 0, 0)) < 0) {
 			outfmt(out2, "trap: %s: bad trap\n", *ap);
 			return 1;
 		}

@@ -400,7 +400,7 @@ out:
 	/* NOTREACHED */
 }
 
-int decode_signal(const char *string, int minsig)
+int decode_signal(const char *string, int minsig, int numonly)
 {
 	int signo;
 

@@ -410,7 +410,8 @@ int decode_signal(const char *string, int minsig)
 			return -1;
 		}
 		return signo;
-	}
+	} else if (numonly)
+		return -1;
 
 	for (signo = minsig; signo < NSIG; signo++) {
 		if (!strcasecmp(string, signal_names[signo])) {

index 7573fd7..edbdb45 100644
@@ -49,7 +49,7 @@ void onsig(int);
 void dotrap(void);
 void setinteractive(int);
 void exitshell(void) __attribute__((__noreturn__));
-int decode_signal(const char *, int);
+int decode_signal(const char *, int, int);
 
 static inline int have_traps(void)
 {

2.4.9 (Apple Git-60)

-- 
Jonathan Perkin  -  Joyent, Inc.  -  www.joyent.com

Thanks for the patch.

I've decided to do something similar to your final patch:

---8<---
Jonathan Perkin submitted a patch to fix the behaviour of trap when the first argument is an integer. Currently it is treated as a command while POSIX requires it to be treated as a signal.

This patch is based on his idea but instead of adding an extra argument to decode_signal I have added a new decode_signum helper.

index 82d4263..edb9938 100644
@@ -79,6 +79,8 @@ int gotsigchld;
 
 extern char *signal_names[];
 
+static int decode_signum(const char *);
+
 #ifdef mkinit
 INCLUDE "trap.h"
 INIT {

@@ -112,7 +114,7 @@ trapcmd(int argc, char **argv)
 		}
 		return 0;
 	}
-	if (!ap[1])
+	if (!ap[1] || decode_signum(*ap) >= 0)
 		action = NULL;
 	else
 		action = *ap++;

@@ -400,18 +402,27 @@ out:
 	/* NOTREACHED */
 }
 
-int decode_signal(const char *string, int minsig)
+static int decode_signum(const char *string)
 {
-	int signo;
+	int signo = -1;
 
 	if (is_number(string)) {
 		signo = atoi(string);
-		if (signo >= NSIG) {
-			return -1;
-		}
-		return signo;
+		if (signo >= NSIG)
+			signo = -1;
 	}
 
+	return signo;
+}
+
+int decode_signal(const char *string, int minsig)
+{
+	int signo;
+
+	signo = decode_signum(string);
+	if (signo >= 0)
+		return signo;
+
 	for (signo = minsig; signo < NSIG; signo++) {
 		if (!strcasecmp(string, signal_names[signo])) {
 			return signo;

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt