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Full Discussion: Shell advanced syntax?
Top Forums Shell Programming and Scripting Shell advanced syntax? Post 302463829 by alister on Monday 18th of October 2010 02:21:16 PM
Old 10-18-2010
Quote:
Originally Posted by alt
because I am expecting no return from export command.
Every single command run on a UNIX/Linux/POSIX system will return an exit status. If that exit status is 0, the shell treats that as a boolean true. Any other exit status is treated as a boolean false.

Regards,
Alister

---------- Post updated at 02:21 PM ---------- Previous update was at 02:14 PM ----------

Quote:
Originally Posted by alister
That's close but not quite correct. The original version's echo executes if the export command fails. This interpretation's does not.

Regards,
Alister

Actually, export always returns a 0 exit status, so it will never fail. Scrutinizer's code should work just as the original.

That said, I'll leave my post as is since that's a very unusual corner case. In just about every other situation, a command can return a non-zero exit status and the constructs would not be logically equivalent.

Regards,
Alister
This User Gave Thanks to alister For This Post:
 

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exit(1)                                                            User Commands                                                           exit(1)

NAME
exit, return, goto - shell built-in functions to enable the execution of the shell to advance beyond its sequence of steps SYNOPSIS
sh exit [n] return [n] csh exit [ ( expr )] goto label ksh *exit [n] *return [n] DESCRIPTION
sh exit will cause the calling shell or shell script to exit with the exit status specified by n. If n is omitted the exit status is that of the last command executed (an EOF will also cause the shell to exit.) return causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command exe- cuted. csh exit will cause the calling shell or shell script to exit, either with the value of the status variable or with the value specified by the expression expr. The goto built-in uses a specified label as a search string amongst commands. The shell rewinds its input as much as possible and searches for a line of the form label: possibly preceded by space or tab characters. Execution continues after the indicated line. It is an error to jump to a label that occurs between a while or for built-in command and its corresponding end. ksh exit will cause the calling shell or shell script to exit with the exit status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing a trap, the last command refers to the command that executed before the trap was invoked. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (See set below) turned on. return causes a shell function or '.' script to return to the invoking script with the return status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a '.' script, then it is the same as an exit. On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways: 1. Variable assignment lists preceding the command remain in effect when the command completes. 2. I/O redirections are processed after variable assignments. 3. Errors cause a script that contains them to abort. 4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
break(1), csh(1), ksh(1), sh(1), attributes(5) SunOS 5.10 15 Apr 1994 exit(1)
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