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Top Forums Shell Programming and Scripting Can I do this without eval? (zsh) Post 302990300 by Corona688 on Tuesday 24th of January 2017 12:12:07 PM
Old 01-24-2017
Quote:
Originally Posted by rovf
I like your idea, because of its simplicity. Its main drawback is that, at least according to my manpage of test, it does not work with the -N file test operator (true if file exists and its access time is not newer than its modification time)
I just tried that out of curiosity and now realize I was slightly wrong.

In most shells, test is a builtin which supports all operators the shell does.

Code:
$ test -N /etc/passwd
$ echo $?
0
$ whereis test
test: /usr/bin/test /usr/share/man/man1/test.1.bz2 /usr/share/man/man1p/test.1p.bz2
$ /usr/bin/test -N /etc/passwd
/usr/bin/test: extra argument '-N'
$

...so if your shell has it as a builtin you are set.

I definitely reccommend against injection rejection which leaves you wide open to things you don't know about and can react badly to valid things you still didn't expect. (What if a filename contains a literal backtick?) Better to not leave the door open in the first place and use something which doesn't allow for shell interpretation.

Last edited by Corona688; 01-24-2017 at 01:19 PM..
 

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TEST(1) 						      General Commands Manual							   TEST(1)

NAME
test, [ - test for a condition SYNOPSIS
test expr [ expr ] OPTIONS
(none) EXAMPLES
test -r file # See if file is readable DESCRIPTION
Test checks to see if files exist, are readable, etc. and returns an exit status of zero if true and nonzero if false. The legal operators are -r file true if the file is readable -w file true if the file is writable -x file true if the file is executable -f file true if the file is not a directory -d file true if the file is a directory -s file true if the file exists and has a size > 0 -t fd true if file descriptor fd (default 1) is a terminal -z s true if the string s has zero length -n s true if the string s has nonzero length s1 = s2 true if the strings s1 and s2 are identical s1 != s2 true if the strings s1 and s2 are different m -eq m true if the integers m and n are numerically equal The operators -gt, -ge, -ne, -le, and -lt may be used as well. These operands may be combined with -a (Boolean and), -o (Boolean or), ! (negation). The priority of -a is higher than that of -o. Parentheses are permitted, but must be escaped to keep the shell from trying to interpret them. SEE ALSO
expr(1), sh(1). TEST(1)
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