Secret command Post: 302255995

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Top Forums UNIX for Advanced & Expert Users Secret command Post 302255995 by Perderabo on Friday 7th of November 2008 02:20:37 PM

11-07-2008

Administrator Emeritus

:() { something }
is attempting to define a function called ":". Not every shell is going to tolerate a function by that name.

it's a bit interesting that this works:

Code:

$ x() { echo hello & } ; x
hello
[1] 5548
[1] + Done                 echo hello
$
$

I guess the ampersand is doing double duty by backgrounding the command and introducing the start of a command. Usually I would expect:
x() { echo hello & ; }
to be correct. As you can see the end of the command simple invokes the function that was defined.

Where you get into trouble is that the function then invokes itself twice. This winds up trying to run an infinite number of processes. It can't, but it runs as much as it can and will keep this up forever.

Perderabo

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echo

ECHO(1) 						    BSD General Commands Manual 						   ECHO(1)

NAME

     echo -- write arguments to the standard output

SYNOPSIS

     echo [-n] [string ...]

DESCRIPTION

     The echo utility writes any specified operands, separated by single blank (' ') characters and followed by a newline ('
') character, to the
     standard output.

     The following option is available:

     -n    Do not print the trailing newline character.

     The end-of-options marker -- is not recognized and written literally.

     The newline may also be suppressed by appending 'c' to the end of the string, as is done by iBCS2 compatible systems.  Note that the -n
     option as well as the effect of 'c' are implementation-defined in IEEE Std 1003.1-2001 (``POSIX.1'') as amended by Cor. 1-2002.  For porta-
     bility, echo should only be used if the first argument does not start with a hyphen ('-') and does not contain any backslashes ('').  If
     this is not sufficient, printf(1) should be used.

     Most shells provide a builtin echo command which tends to differ from this utility in the treatment of options and backslashes.  Consult the
     builtin(1) manual page.

EXIT STATUS

     The echo utility exits 0 on success, and >0 if an error occurs.

SEE ALSO

     builtin(1), csh(1), printf(1), sh(1)

STANDARDS

     The echo utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'') as amended by Cor. 1-2002.

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