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Top Forums Shell Programming and Scripting When does an if statement need parentheses Post 302546072 by DGPickett on Wednesday 10th of August 2011 10:22:19 AM
Old 08-10-2011
Shell if with no parens takes a single command execution string, possibly piped and subshell'd (), and a $? of 0 is true, like "if grep -q haha logfile ; then . . . ." The $? is from the last command, as I recall, so "if find . -type f|grep -q .profile ; then . . . ." tests the exit() value of grep and "if ( find . -type f >/tmp/myfiles ; grep -q .profile /tmp/myfiles ); then . . . ." also tests grep. (An extra fork() and named file open twice is probably more expensive than a pipe() call, slower because of latency and leaves a file behind.)
 

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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 file name 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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