Loop breaks through ssh in script Post: 302875015

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Operating Systems AIX Loop breaks through ssh in script Post 302875015 by bakunin on Monday 18th of November 2013 09:40:00 AM

11-18-2013

Registered User

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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git-merge-index

GIT-MERGE-INDEX(1)						    Git Manual							GIT-MERGE-INDEX(1)

NAME

       git-merge-index - Run a merge for files needing merging

SYNOPSIS

       git merge-index [-o] [-q] <merge-program> (-a | [--] <file>*)

DESCRIPTION

       This looks up the <file>(s) in the index and, if there are any merge entries, passes the SHA-1 hash for those files as arguments 1, 2, 3
       (empty argument if no file), and <file> as argument 4. File modes for the three files are passed as arguments 5, 6 and 7.

OPTIONS

       --
	   Do not interpret any more arguments as options.

       -a
	   Run merge against all files in the index that need merging.

       -o
	   Instead of stopping at the first failed merge, do all of them in one shot - continue with merging even when previous merges returned
	   errors, and only return the error code after all the merges.

       -q
	   Do not complain about a failed merge program (a merge program failure usually indicates conflicts during the merge). This is for
	   porcelains which might want to emit custom messages.

       If git merge-index is called with multiple <file>s (or -a) then it processes them in turn only stopping if merge returns a non-zero exit
       code.

       Typically this is run with a script calling Git's imitation of the merge command from the RCS package.

       A sample script called git merge-one-file is included in the distribution.

       ALERT ALERT ALERT! The Git "merge object order" is different from the RCS merge program merge object order. In the above ordering, the
       original is first. But the argument order to the 3-way merge program merge is to have the original in the middle. Don't ask me why.

       Examples:

	   torvalds@ppc970:~/merge-test> git merge-index cat MM
	   This is MM from the original tree.			 # original
	   This is modified MM in the branch A. 		 # merge1
	   This is modified MM in the branch B. 		 # merge2
	   This is modified MM in the branch B. 		 # current contents

       or

	   torvalds@ppc970:~/merge-test> git merge-index cat AA MM
	   cat: : No such file or directory
	   This is added AA in the branch A.
	   This is added AA in the branch B.
	   This is added AA in the branch B.
	   fatal: merge program failed

       where the latter example shows how git merge-index will stop trying to merge once anything has returned an error (i.e., cat returned an
       error for the AA file, because it didn't exist in the original, and thus git merge-index didn't even try to merge the MM thing).

GIT

       Part of the git(1) suite

Git 1.8.5.3							    01/14/2014							GIT-MERGE-INDEX(1)

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