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Operating Systems Linux Red Hat Script creates additional file Post 303000816 by MadeInGermany on Thursday 20th of July 2017 07:27:02 AM
Old 07-20-2017
[[ ]] and [ ] work similar, but the implementation is different.
Code:
$ type [
[ is a shell builtin
$ type [[
[[ is a shell keyword

The [ is a builtin command. In fact it is an alias of the test command. (When run as [ the last argument must be ]. Command arguments may be redirected with < and >, and that is what caused your problem. The redirection can be prevented by quoting "<" ">" or \< \>, but the standard operators are -lt and -gt. As with all command arguments, you should use "quotes" to prevent word splitting and globbing.
The [[ ]] is a compound, built into the shell interpreter. Because it is not a command, its content can be freely designed, and in fact a < and > are valid integer comparators. And the values are not subject to globbing, and word splitting happens before variable substitution (i.e. you need to quote "two words" to be seen as one value but not $word even if it's value is "two words").
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RBASH(1)						      General Commands Manual							  RBASH(1)

NAME
rbash - restricted bash, see bash(1) RESTRICTED SHELL
If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the exception that the follow- ing are disallowed or not performed: o changing directories with cd o setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV o specifying command names containing / o specifying a filename containing a / as an argument to the . builtin command o specifying a filename containing a slash as an argument to the -p option to the hash builtin command o importing function definitions from the shell environment at startup o parsing the value of SHELLOPTS from the shell environment at startup o redirecting output using the >, >|, <>, >&, &>, and >> redirection operators o using the exec builtin command to replace the shell with another command o adding or deleting builtin commands with the -f and -d options to the enable builtin command o using the enable builtin command to enable disabled shell builtins o specifying the -p option to the command builtin command o turning off restricted mode with set +r or set +o restricted. These restrictions are enforced after any startup files are read. When a command that is found to be a shell script is executed, rbash turns off any restrictions in the shell spawned to execute the script. SEE ALSO
bash(1) GNU Bash-4.0 2004 Apr 20 RBASH(1)
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