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Top Forums UNIX for Advanced & Expert Users Variable assignments specified with eval shell built-in Post 302486390 by Scrutinizer on Saturday 8th of January 2011 06:51:07 AM
Variable assignments specified with eval shell built-in

According to the POSIX specifications eval is a special shell built-in, which should imply that variable assignments specified together with it should remain in effect after the built-in completes. Thus one would expect IFS to be changed after this:
Code:
var=$'a\nb c'
$ IFS=$'\n' eval '
for i in $var; do
  echo "$i"
done'
a
b c

But it isn't:
Code:
$ set | grep ^IFS
IFS=$' \t\n'


Last edited by fpmurphy; 01-08-2011 at 11:43 AM.. Reason: fixed link
 
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exec(1) 							   User Commands							   exec(1)

NAME
exec, eval, source - shell built-in functions to execute other commands SYNOPSIS
sh exec [argument...] eval [argument...] csh exec command eval argument... source [-h] name ksh *exec [arg...] *eval [arg...] DESCRIPTION
sh The exec command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may appear and, if no other arguments are given, cause the shell input/output to be modified. The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed. csh exec executes command in place of the current shell, which terminates. eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as the result of command or variable substitution. source reads commands from name. source commands may be nested, but if they are nested too deeply the shell may run out of file descrip- tors. An error in a sourced file at any level terminates all nested source commands. -h Place commands from the file name on the history list without executing them. ksh With the exec built-in, if arg is given, the command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to mod- ify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program. The arguments to eval are read as input to the shell and the resulting command(s) executed. On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways: 1. Variable assignment lists preceding the command remain in effect when the command completes. 2. I/O redirections are processed after variable assignments. 3. Errors cause a script that contains them to abort. 4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. EXIT STATUS
For ksh: If command is not found, the exit status is 127. If command is found, but is not an executable utility, the exit status is 126. If a redi- rection error occurs, the shell exits with a value in the range 1-125. Otherwise, exec returns a zero exit status. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
csh(1), ksh(1), sh(1), attributes(5) SunOS 5.10 17 Jul 2002 exec(1)

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