Tcl Source Code

If the name contains a slash then it must refer to an executable
reachable from the current directory.
No
.QW glob
expansion or other shell-like substitutions
are performed on the arguments to commands.
.SH "PORTABILITY ISSUES"

.SS "WINDOWS (all versions)"
.PP
Reading from or writing to a socket, using the
.QW \fB@\0\fIfileId\fR
notation, does not work.  When reading from a socket, a 16-bit DOS
application will hang and a 32-bit application will return immediately with
end-of-file.  When either type of application writes to a socket, the
information is instead sent to the console, if one is present, or is
discarded.

.PP
Note that the current escape resp. quoting of arguments for windows works only
with executables using CommandLineToArgv, CRT-library or similar, as well as
with the windows batch files (excepting the newline, see below).
Although it is the common escape algorithm, but, in fact, the way how the
executable parses the command-line (resp. splits it into single arguments)
is decisive.
.PP
Unfortunately, there is currently no way to supply newline character within
an argument to the batch files (\fB.cmd\fR or \fB.bat\fR) or to the command
processor (\fBcmd.exe /c\fR), because this causes truncation of command-line
(also the argument chain) on the first newline character.
But it works properly with an executable (using CommandLineToArgv, etc).
.PP
.RS
.PP
\fBArgument quoting\fR
.PP
The arguments of the \fBexec\fR command are mapped to the arguments of the called
program. Additional quote characters (\fB"\fR) are automatically  added around
arguments if expected. Special characters are escaped by inserting backslash
characters.
.PP
The MS-Windows environment does execute programs mentioned in the arguments and
called batch files (conspec) replace environment variables, which may have side
effects (vulnerabilities) or break any already existing quoting (for example,
if the environment variable contains a special character like a \fB"\fR).
Examples are:
.PP
.CS
% exec my-echo.cmd {test&whoami}
  test
  mylogin
% exec my-echo.cmd "ENV X:%X%"
  ENV X: CONTENT OF X
.CE
.PP
The following formatting is automatically performed on any
argument item to avoid subprogram execution:
Any special character argument containing a special character (\fB&\fR, \fB|\fR,
\fB^\fR, \fB<\fR, \fB>\fR, \fB!\fR, \fB(\fR, \fB)\fR, \fB(\fR, \fB%\fR)
is automatically enclosed in quotes (\fB"\fR). Any data quote is escaped by
insertion of backslash characters.
.PP

.IP \(bu 3
The directories listed in the path.
.PP
In order to execute shell built-in commands like \fBdir\fR and \fBcopy\fR,
the caller must prepend the desired command with
.QW "\fBcmd.exe /c\0\fR"
because built-in commands are not implemented using executables.


.SS UNIX (including Mac OS X)
.PP
The \fBexec\fR command is fully functional and works as described.
.SH "UNIX EXAMPLES"
.PP
Here are some examples of the use of the \fBexec\fR command on Unix.
To execute a simple program and get its result:
.PP
.CS