`sh` Provider

The sh provider makes available probes that can be used to observe the behavior of bourne shell scripts.

This provider is in development and is not currently available

Probes

Probe	Description
`builtin-entry`	Fires on entry to a shell builtin command.
`builtin-return`	Fires on return from a shell builtin command.
`command-entry`	Fires when the shell execs an external command.
`command-return`	Fires on return from an external command.
`function-entry`	Fires on entry into a shell function.
`function-return`	Fires on return from a shell function.
`line`	Fires before commands on a particular line of code are executed.
`subshell-entry`	Fires when the shell forks a subshell.
`subshell-return`	Fires on return from a forked subshell.
`script-start`	Fires before any commands in a script are executed.
`script-done`	Fires on script exit.
`variable-set`	Fires on assignment to a variable.
`variable-unset`	Fires when a variable is unset.

Note that the use of non-empty module or function names in a sh* probe is undefined at this time.

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`sh` Probe Arguments

Probe	`args[0]`	`args[1]`	`args[2]`	`args[3]`	`args[4]`
`builtin-entry,command-entry,function-entry`	`char *`	`char *`	`int`	`int`	`char **`
`builtin-return,command-return,function-return`	`char *`	`char *`	`int`
`subshell-entry`	`char *`	`pid_t`
`subshell-return`	`char *`	`int`
`line`	`char *`	`int`
`script-start`	`char *`
`script-done`	`char *`	`int`
`variable-set`	`char *`	`char *`	`char *`
`variable-unset`	`char *`	`char *`

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`sh` Probe Arguments - more detail

`builtin-entry,command-entry,function-entry`

`char *`	`args[0]`	Script Name
`char *`	`args[1]`	Builtin/Command/Function Name
`int`	`args[2]`	Line Number
`int`	`args[3]`	# Arguments
`char **`	`args[4]`	Pointer to argument list

`builtin-return,command-return,function-return`

`char *`	`args[0]`	Script Name
`char *`	`args[1]`	Builtin/Command/Function Name
`int`	`args[2]`	Return Value

`subshell-entry`

`char *`	`args[0]`	Script Name
`pid_t`	`args[1]`	Forked Process ID

`subshell-return`

`char *`	`args[0]`	Script Name
`int`	{{args[1]	Return Value

`line`

`char *`	`args[0]`	Script Name
`int`	`args[1]`	Line Number

`script-start`

char * args[0] Script Name

`script-done`

`char *`	`args[0]`	Script Name
`int`	`args[1]`	Exit Value

`variable-set`

`char *`	`args[0]`	Script Name
`char *`	`args[1]`	Variable Name
`char *`	`args[2]`	Value

`variable-unset`

`char *`	`args[0]`	Script Name
`char *`	`args[1]`	Variable Name

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Examples

Some simple examples of sh provider usage follow.

Catching a variable assignment

Say we want to determine which line in the following script has an assignment to WatchedVar:

#!/bin/sh

# starting script
WatchedVar=Value
unset WatchedVar
# ending script

We could use the following script

#!/usr/sbin/dtrace -s

#pragma D option quiet

sh$target:::line { self->line = arg1; }
sh$target:::variable-set /copyinstr(arg1) == "WatchedVar"/ {
        printf("%d: %s=%s\n", self->line, copyinstr(arg1),
	    copyinstr(arg2)); }
sh$target:::variable-unset /copyinstr(arg1) == "WatchedVar"/ {
        printf("%d: unset %s\n", self->line, copyinstr(arg1)); }

$ ./watch.d -c ./var.sh
4: WatchedVar=Value
5: unset WatchedVar

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Watching the time spent in functions

#!/usr/sbin/dtrace -s

#pragma D option quiet

sh$target:::function-entry { self->start = vtimestamp }
sh$target:::function-return {
	@[copyinstr(arg1)] = quantize(vtimestamp - self->start)
}

Similar for the other entry/return probes, with the exception of subshell as the probe name is unavailable.

Wasted time using external functions instead of builtins

This script is copied from the DTrace toolkit. It's function and how it works should be relatively self explanatory.

#!/usr/sbin/dtrace -Zs
/*
 * sh_wasted.d - measure Bourne shell elapsed times for "wasted" commands.
 *               Written for the sh DTrace provider.
 *
 * $Id: sh_wasted.d 25 2007-09-12 09:51:58Z brendan $
 *
 * USAGE: sh_wasted.d { -p PID | -c cmd }       # hit Ctrl-C to end
 *
 * This script measures "wasted" commands - those which are called externally
 * but are in fact builtins to the shell. Ever seen a script which calls
 * /usr/bin/echo needlessly? This script measures that cost.
 *
 * FIELDS:
 *              FILE            Filename of the shell or shellscript
 *              NAME            Name of call
 *              TIME            Total elapsed time for calls (us)
 *
 * IDEA: Mike Shapiro
 *
 * Filename and call names are printed if available.
 *
 * COPYRIGHT: Copyright (c) 2007 Brendan Gregg.
 *
 * CDDL HEADER START
 *
 *  The contents of this file are subject to the terms of the
 *  Common Development and Distribution License, Version 1.0 only
 *  (the "License").  You may not use this file except in compliance
 *  with the License.
 *
 *  You can obtain a copy of the license at Docs/cddl1.txt
 *  or http://www.opensolaris.org/os/licensing.
 *  See the License for the specific language governing permissions
 *  and limitations under the License.
 *
 * CDDL HEADER END
 *
 * 09-Sep-2007  Brendan Gregg   Created this.
 */

#pragma D option quiet

dtrace:::BEGIN
{
        isbuiltin["echo"] = 1;
        isbuiltin["test"] = 1;
        /* add builtins here */

        printf("Tracing... Hit Ctrl-C to end.\n");
        self->start = timestamp;
}

sh$target:::command-entry
{
        self->command = timestamp;
}

sh$target:::command-return
{
        this->elapsed = timestamp - self->command;
        this->path = copyinstr(arg1);
        this->cmd = basename(this->path);
}

sh$target:::command-return
/self->command && !isbuiltin[this->cmd]/
{
        @types_cmd[basename(copyinstr(arg0)), this->path] = sum(this->elapsed);
        self->command = 0;
}

sh$target:::command-return
/self->command/
{
        @types_wasted[basename(copyinstr(arg0)), this->path] =
            sum(this->elapsed);
        self->command = 0;
}

proc:::exit
/pid == $target/
{
        exit(0);
}

dtrace:::END
{
        this->elapsed = (timestamp - self->start) / 1000;
        printf("Script duration: %d us\n", this->elapsed);

        normalize(@types_cmd, 1000);
        printf("\nExternal command elapsed times,\n");
        printf("   %-30s %-22s %8s\n", "FILE", "NAME", "TIME(us)");
        printa("   %-30s %-22s %@8d\n", @types_cmd);

        normalize(@types_wasted, 1000);
        printf("\nWasted command elapsed times,\n");
        printf("   %-30s %-22s %8s\n", "FILE", "NAME", "TIME(us)");
        printa("   %-30s %-22s %@8d\n", @types_wasted);
}

Given the following silly little script (bad.sh), we can look at the amount of time spent executing external commands and split out the time that has been spent on commands we've defined that could have been builtins.

#!/bin/sh

for i in 0 1 2 3 4 5 6 7 8 9
do      for j in 0 1 2 3 4 5 6 7 8 9
        do      /bin/echo "$i$j \c"
                /bin/date
        done
done

$ ./sh_wasted.d -c ./bad.sh
Tracing... Hit Ctrl-C to end.
00 Wed Jan  9 10:53:02 EST 2008
01 Wed Jan  9 10:53:03 EST 2008
02 Wed Jan  9 10:53:03 EST 2008
...
98 Wed Jan  9 10:53:20 EST 2008
99 Wed Jan  9 10:53:20 EST 2008
Script duration: 17998139 us

External command elapsed times,
   FILE                           NAME                   TIME(us)
   bad.sh                         /bin/date               1067426

Wasted command elapsed times,
   FILE                           NAME                   TIME(us)
   bad.sh                         /bin/echo               1040886

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Stability

The sh provider uses DTrace's stability mechanism to describe its stabilities, as shown in the following table. For more information about the stability mechanism, see Chapter 39, Stability.

Element	Name stability	Data stability	Dependency class
Provider	Unstable	Unstable	Common
Module	Private	Private	Unknown
Function	Private	Private	Unknown
Name	Unstable	Unstable	Common
Arguments	Unstable	Unstable	Common

sh Provider

sh Provider

Probes

sh Probe Arguments

sh Probe Arguments - more detail

builtin-entry,command-entry,function-entry

builtin-return,command-return,function-return

subshell-entry

subshell-return

line

script-start

script-done

variable-set

variable-unset