A string between $' and ' may contain backslash escape sequences similar to
the ones in a C string constant (except that a single-quote must be escaped
and a double-quote need not be). Details are in the sh(1) man page.
This construct is useful to include unprintable characters, tabs and
newlines in strings; while this can be done with a command substitution
containing a printf command, that needs ugly workarounds if the result is to
end with a newline as command substitution removes all trailing newlines.
The construct may also be useful in future to describe unprintable
characters without needing to write those characters themselves in 'set -x',
'export -p' and the like.
The implementation attempts to comply to the proposal for the next issue of
the POSIX specification. Because this construct is not in POSIX.1-2008,
using it in scripts intended to be portable is unwise.
Matching the minimal locale support in the rest of sh, the \u and \U
sequences are currently not useful.
Exp-run done by: pav (with some other sh(1) changes)
Note that this only applies to variables that are actually used.
Things like (0 && unsetvar) do not cause an error.
Exp-run done by: pav (with some other sh(1) changes)
In particular, this makes things like ${#foo[0]} and ${#foo[@]} errors
rather than silent equivalents of ${#foo}.
PR: bin/151720
Submitted by: Mark Johnston
Exp-run done by: pav (with some other sh(1) changes)
For backgrounded pipelines and subshells, the previous value of $? was being
preserved, which is incorrect.
For backgrounded simple commands containing a command substitution, the
status of the last command substitution was returned instead of 0.
If fork() fails, this is an error.
If the -p option is turned off, privileges from a setuid or setgid binary
are dropped. Make sure to check if this succeeds. If it fails, this is an
error which will cause the shell to abort except in interactive mode or if
'command' was used to make 'set' or an outer 'eval' or '.' non-special.
Note that taking advantage of this feature and writing setuid shell scripts
seems unwise.
MFC after: 1 week
If EV_EXIT causes an exit, use the exception mechanism to unwind
redirections and local variables. This way, if the final command is a
redirected command, an EXIT trap now executes without the redirections.
Because of these changes, EV_EXIT can now be inherited by the body of a
function, so do so. This means that a function no longer prevents a fork
before an exec being skipped, such as in
f() { head -1 /etc/passwd; }; echo $(f)
Wrapping a single builtin in a function may still cause an otherwise
unnecessary fork with command substitution, however.
An exit command or -e failure still invokes the EXIT trap with the
original redirections and local variables in place.
Note: this depends on SHELLPROC being gone. A SHELLPROC depended on
keeping the redirections and local variables and only cleaning up the
state to restore them.
This is only a problem if IFS contains digits, which is unusual but valid.
Because of an incorrect fix for PR bin/12137, "${#parameter}" was treated
as ${#parameter}. The underlying problem was that "${#parameter}"
erroneously added CTLESC bytes before determining the length. This
was properly fixed for PR bin/56147 but the incorrect fix was not backed
out.
Reported by: Seeker on forums.freebsd.org
MFC after: 2 weeks
POSIX does not require the shell to fork for a subshell environment, and we
use that possibility in various ways (command substitutions with a single
command and most subshells that are the final command of a shell process).
Therefore do not tie subshells to forking in the man page.
Command substitutions with expansions are a bit strange, causing a fork for
$(...$(($x))...) because $x might expand to y=2; they will probably be
changed later but this is how they work now.
These already worked: $# ${#} ${##} ${#-} ${#?}
These now work as well: ${#+word} ${#-word} ${##word} ${#%word}
There is an ambiguity in the standard with ${#?}: it could be the length of
$? or it could be $# giving an error in the (impossible) case that it is not
set. We continue to use the former interpretation as it seems more useful.
New features:
* proper lazy evaluation of || and &&
* ?: ternary operator
* executable is considerably smaller (8K on i386) because lex and yacc are
no longer used
Differences from dash:
* arith_t instead of intmax_t
* imaxdiv() not used
* unset or null variables default to 0
* let/exp builtin (undocumented, will probably be removed later)
Obtained from: dash
* In {(...) <redir1;} <redir2, do not drop redir1.
* Maintain the difference between (...) <redir and {(...)} <redir:
In (...) <redir, the redirection is performed in the child, while in
{(...)} <redir it should be performed in the parent (like {(...); :;}
<redir)
POSIX requires this and it is simpler than the previous code that remembered
command locations when appending directories to PATH.
In particular,
PATH=$PATH
is no longer a no-op but discards all cached command locations.
If execve() returns an [ENOEXEC] error, check if the file is binary before
trying to execute it using sh. A file is considered binary if at least one
of the first 256 bytes is '\0'.
In particular, trying to execute ELF binaries for the wrong architecture now
fails with an "Exec format error" message instead of syntax errors and
potentially strange results.
These are called "shell procedures" in the source.
If execve() failed with [ENOEXEC], the shell would reinitialize itself
and execute the program as a script. This requires a fair amount of code
which is not frequently used (most scripts have a #! magic number).
Therefore just execute a new instance of sh (_PATH_BSHELL) to run the
script.
This matches the constants from <signal.h> with 'SIG' removed, which POSIX
requires kill and trap to accept and 'kill -l' to write.
'kill -l', 'trap', 'trap -l' output is now upper case.
In Turkish locales, signal names with an upper case 'I' are now accepted,
while signal names with a lower case 'i' are no longer accepted, and the
output of 'killall -l' now contains proper capital 'I' without dot instead
of a dotted capital 'I'.
* There is no plan for an alternative to the command "set".
* Attempting to unset a readonly variable has not raised an error for quite
a while, so the order of unsetting a variable and a function with the same
name does not matter.
MFC after: 1 week
When a foreground job exits on a signal, a message is printed to stdout
about this. The buffer was not flushed after this which could result in the
message being written to the wrong file if the next command was a builtin
and had stdout redirected.
Example:
sh -c 'kill -9 $$'; : > foo; echo FOO:; cat foo
Reported by: gcooper
MFC after: 1 week
This is useful so that it is easier to exit on a signal than to reset the
trap to default and resend the signal. It matches ksh93. POSIX says that
'exit' without args from a trap action uses the exit status from the last
command before the trap, which is different from 'exit $?' and matches this
if the previous command is assumed to have exited on the signal.
If the signal is SIGSTOP, SIGTSTP, SIGTTIN or SIGTTOU, or if the default
action for the signal is to ignore it, a normal _exit(2) is done with exit
status 128+signal_number.
* Make 'trap --' do the same as 'trap' instead of nothing.
* Make '--' stop option processing (note that '-' action is not an option).
Side effect: The error message for an unknown option is different.
All builtins are now always found before a PATH search.
Most ash derivatives have an undocumented feature where the presence of an
entry "%builtin" in $PATH will cause builtins to be checked at that point of
the PATH search, rather than before looking at any directories as documented
in the man page (very old versions do document this feature).
I am removing this feature from sh, as it complicates the code, may violate
expectations (for example, /usr/bin/alias is very close to a forkbomb with
PATH=/usr/bin:%builtin, only /usr/bin/builtin not being another link saves
it) and appears to be unused (all the %builtin google code search finds is
in some sort of ash source code).
Note that aliases and functions took and take precedence above builtins.
Because aliases work on a lexical level they can only ever be overridden on
a lexical level (quoting or preceding 'builtin' or 'command'). Allowing
override of functions via PATH does not really fit in the model of sh and it
would work differently from %builtin if implemented.
Note: POSIX says special builtins are found before functions. We comply to
this because we do not allow functions with the same name as a special
builtin.
Silence from: freebsd-hackers@ (message sent 20101225)
Discussed with: dougb
