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Full Discussion: Loop breaks through ssh in script
Operating Systems AIX Loop breaks through ssh in script Post 302875015 by bakunin on Monday 18th of November 2013 09:40:00 AM
Old 11-18-2013
Quote:
Originally Posted by omonoiatis9
i use the backticks because this way i tell the script if the command inside the backticks executes successfully then proceed. else if the command fails it doesnt get into the if statement.
No, no and again: no.

First, the "if"-statement:

The if-statement is defined as:
Code:
if command ; then commandA ; else commandB ; fi

command can be any command, simple or complex. In either way its return code is used to determine if the then-branch or the else-branch is executed. If the return code ("$?") is 0 (zero), the then-branch is executed, otherwise the else-branch.

The probably most often-used command in this position is /usr/bin/test or its counterpart /usr/bin/[. Both work the same way (the difference being that "[" requires "]" as the last argument): if the tests specified as arguments add up to a boolean TRUE it returns 0, for a boolean FALSE it returns 1.

Still, the same way as you use test you can use any other command. For instance:

Code:
if grep -q EXPR /some/file ; then

will execute the then-branch if EXPR is found in /some/file and the else-branch if not, because grep will return 0 if it finds what is searched for and 1 if it doesn't.

Second: the backticks.

Even if you need process substitution (which isn't the case, see above), you should NOT use backticks - not the last 20 years or so. Even ksh88 already had "$(...)" instead of "`...`", which is not only nestable, but also the POSIX-compatible way to enclose a process. Backticks are supported only for one reason: backwards compatibility. There is absolutely no reason to use them any more, because they offer absolutely no advantage over "$(...)", only drawbacks.

I hope this helps.

bakunin
 

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LEARN ABOUT CENTOS

prdb.db0

PRDB.DB0(5)							AFS File Reference						       PRDB.DB0(5)

NAME

       prdb.DB0, prdb.DBSYS1 - Contain the Protection Database and associated log

DESCRIPTION

       The prdb.DB0 file contains the Protection Database, which maps AFS user, machine, and group names to their respective IDs (AFS UIDs and
       GIDs) and tracks group memberships. The Protection Server (ptserver process) uses the information in the database to help the File Server
       grant data access to authorized users.

       The prdb.DBSYS1 file is a log file in which the Protection Server logs each database operation before performing it.  When an operation is
       interrupted, the Protection Server replays the log to complete the operation.

       Both files are in binary format and reside in the /var/lib/openafs/db directory on each of the cell's database server machines. When the
       Protection Server starts or restarts on a given machine, it establishes a connection with its peers and verifies that its copy of the
       database matches the copy on the other database server machines. If not, the Protection Servers call on AFS's distributed database
       technology, Ubik, to distribute to all of the machines the copy of the database with the highest version number.

       Always use the commands in the pts suite to administer the Protection Database. It is advisable to create an archive copy of the database
       on a regular basis, using a tool such as the UNIX tar command.

SEE ALSO

       prdb_check(8), pts(1), ptserver(8)

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OpenAFS 							    2012-03-26							       PRDB.DB0(5)
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