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Top Forums UNIX for Advanced & Expert Users concurrency issue while Accessing Mail Box from shell script Post 302108253 by Perderabo on Sunday 25th of February 2007 12:49:08 PM
Old 02-25-2007
You don't say what os you're using, what language you're trying to use, or give much info on how the script is used (always for one particular user? for everyone on the system?). I will assume that you're using Solaris 10, trying to program in ksh, and running the script for every user on the box. If these assumptions are wrong, your mileage may vary.

There are several problems with your code. I see the comment where you claim the mailfile is always blank. But the code which is present to handle a non-blank mailfile is guaranteed to fail and should be removed. Leaving broken remnants of old code in a script is asking for trouble down the road. I have never seen syntax like:
while ( [ $mailstat -eq 0 ] )
I think that may be legal. It might even be useful with a much more complex test. The normal syntax is:
while [ $mailstat -eq 0 ]
Your parentheses are demanding that the test be preformed in a subshell. The exit code of the subshell should be the exit code of the [ command in this case. But you are starting an extra process for no good reason. More to the point, the loop is not useful. You should be doing:
1) check for existence of mail, exit if none
2) save any mail present

There is a concurrency issue here... mail may be present during step 1 and absent during step 2. Step 2 needs to accept that...it is not an error. Step 2 should be a one shot deal, not a loop. If new mail arrives immediately after the save, your script will get to it the next time it is launched. You are looping, probably not to handle newly arrived mail, but rather to handle one message at a time. That is not efficient. "save * filename" will grab all of the mail at once. It is more efficient and eliminates most of your problem.

mailx initializes itself by processing a system-wide startup script. Then it processes a user specific startup script. A -n will inhibit the former but not the latter. The mailx man page says the save command "Save the specified messages in the given file. The file is created if it does not exist. The file defaults to mbox. The message is deleted from the mailbox when mailx terminates unless keepsave is set (see also Internal Variables and the exit and quit commands). If a user has a .mailrc that sets keepsave, your script will not empty his mailbox. This is my best guess as to why you have your current problem and I don't know what to suggest. I don't think you should override a user's wishes without consulting with the user in question.
 

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mailfrom(1)						      General Commands Manual						       mailfrom(1)

NAME
mailfrom - summarize mail folders by subject and sender SYNOPSIS
status] [folder|username]... DESCRIPTION
The command reads one or more mail folders and outputs one line per message in the form: from [subject] where from is the name of the person the message is from, and subject is the subject of the message, if present. If determines that the message is from you, the from portion will read where user is the user the message was sent to. This happens when you receive a copy of a letter you sent. The default folder is your incoming mailbox, See the Operands subsection below. Options recognizes the following options: Print a brief help message summarizing the options. Number the messages using the same numbering scheme used by Very quiet mode. Only error messages are produced. This option is useful in shell scripts, where only the success or failure of the program is important, and output is not desired. Quiet mode. Output only a one-line summary for each mailbox or folder. Add a summary of the number of messages by message status in each mailbox or folder. To get the summary only, use this with the option. The summary has the form: If an item count, n, r, or u is zero, the line is omitted. Only display headers from messages with the given status. status can be one of or and are equivalent. The option can be repeated to print header information from more than one category, for example, only new and unread messages. The values can be abbreviated to their first letters. The default is all messages. Tidy mode. If the from field is long enough to displace the subject field from its normal start column, move the subject down onto the next line. Verbose mode. Print a descriptive header before listing the contents of each mailbox or folder. Operands recognizes the following optional operands: folder|username A file name or the name of a mail user on your system. You can use the format to specify a folder in your mail directory, defined by the string variable in your configuration file. searches for the value as a file name relative to your current directory. Then, if the file name is not an absolute path, it searches for the value relative to the incoming mailbox directory, The first file found is selected. You must have read access to the file. RETURN VALUE
returns the following values: Messages matching status are present. No messages matching status are present, but there are some messages. There are no messages at all. An error occurred. If multiple mailboxes or folders are specified, the exit status only applies to the last one examined. This can be used in scripts to determine what kind of mail a user has. EXAMPLES
Display header information from all the messages in your mailbox. Display header information from all new messages in your mailbox. Assuming you have the proper file permissions to read mail, print out header information from all new and unread messages in incoming mail- box. Print only a summary of how many new, unread, and read messages are in your incoming mailbox. AUTHOR
was developed by HP. FILES
Your configuration file. Directory of incoming mailboxes. SEE ALSO
elm(1), mail(1), mailx(1), readmail(1). mailfrom(1)
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