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The Lounge What is on Your Mind? Echo eval xargs and other siblings Post 303031498 by Corona688 on Friday 1st of March 2019 10:32:16 AM
Old 03-01-2019
Shell evaluation is done automatically, by the shell, before a command is run. None of these except eval do shell evaluation; eval can do so because it's actually part of the shell!

By the same ticket, ls abc* is not a feature of ls. abc* gets evaluated by the shell before ls is executed.

I'm not sure what your >stdin stdin> are about. eval does not use stdin or stdout especially, unless the command it's evaluating does. It has no limits at all. That's what makes it dangerous.

One unique feature of xargs is that it parses single and double quotes. Usually this is considered an annoyance and worked around, but this can be used to your advantage, i.e. to split strings containing quotes without resorting to eval.
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ENVSTORE(1)						    BSD General Commands Manual 					       ENVSTORE(1)

NAME
envstore -- save and restore environment variables SYNOPSIS
envstore command [args ...] DESCRIPTION
envstore can save and restore environment variables, thus transferring them between different shells. command must be one of clear Forget all stored variables eval Produce shell code for evaluation, restoring all saved variables list List saved variables in better readable format save variable [value] Save variable either with its current shell value or with value rm variable Remove variable from store Note: Only the first character of command is checked, so envstore e instead of envstore eval, envstore c for envstore clear, etc., are also valid. ENVIRONMENT
ENVSTORE_FILE The file in which the environment parameters are stored, /tmp/envstore-EUID by default, LIMITATIONS
Variable names or values must not contain null bytes or newlines. Due to limitations imposed by most shells, it is not possible to save parameters containing more than one consecutive whitespace. envstore will save and display them correctly, but unless you do IFS trickery, your shell will not be able to load them. The current maximum length (in bytes) is 255 bytes for the variable name and 1023 bytes for its content. AUTHOR
envstore was written by Daniel Friesel <derf@derf.homelinux.org>. Original idea and script by Maximilian Gass <mxey@ghosthacking.net>. SEE ALSO
envify(1) BSD
December 1, 2009 BSD
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