use some part of variable value to replace ../../ values in a file Post: 302645795

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Top Forums Shell Programming and Scripting use some part of variable value to replace ../../ values in a file Post 302645795 by rbatte1 on Thursday 24th of May 2012 05:50:52 AM

05-24-2012

Moderator

I always worry about marking relative references in scripts. If something doesn't exist, a cd will just refuse and unless you carefully manage errors, then you could end up damaging important files. Consider:-

Code:

cd /etc
grep -v bankhost hosts > dr_test_hosts
cd /disaster
rm *
cp -pR /etc/* .

This would (probably in a bad way anyway) remove a sensitive remote host address from /etc/hosts in preparation for a DR test to reduce the risk of actually sending data to the bank. Of course, if you run this and /disaster does not exist then you empty /etc, which could be a little awkward, to say the least.

Could it be a better plan to have a variable made of several others, such as:

Code:

maindir=/dir1/dir2
val=${maindir}/dir3/dir4/file1
...do something...
val=${maindir}/dir3/newdir4/file2
...do something...
val=${maindir}/dir3/bigdir4/file3
...do something...

You would still have to check that these exist, of course, but it reduces the risk of a typing error and one action compounding on another.

Maybe I'm paranoid, but unless you consider every possible action and error, then it's a dangerous game. I've been bitten in the past, so I can't claim perfection, just learning from experience.

I hope that this helps,
Robin
Liverpool/Blackburn
UK

rbatte1

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LEARN ABOUT OPENSOLARIS

dircmp

dircmp(1)							   User Commands							 dircmp(1)

NAME

       dircmp - directory comparison

SYNOPSIS

       dircmp [-ds] [-w n] dir1 dir2

DESCRIPTION

       The  dircmp  command  examines dir1 and dir2 and generates various tabulated information about the contents of the directories. Listings of
       files that are unique to each directory are generated for all the options. If no option is entered, a list is output indicating whether the
       file names common to both directories have the same contents.

OPTIONS

       The following options are supported:

       -d      Compares  the  contents	of  files with the same name in both directories and output a list telling what must be changed in the two
	       files to bring them into agreement. The list format is described in diff(1).

       -s      Suppresses messages about identical files.

       -w n    Changes the width of the output line to n characters. The default width is  72.

OPERANDS

       The following operands are supported:

       dir1    A path name of a directory to be compared.
       dir2

USAGE

       See largefile(5) for the description of the behavior of dircmp when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

ENVIRONMENT VARIABLES

       See environ(5) for descriptions of the following environment variables that affect the execution of dircmp: LC_COLLATE,	LC_CTYPE,  LC_MES-
       SAGES, and NLSPATH.

EXIT STATUS

       The following exit values are returned:

       0     Successful completion.

       >0    An error occurred. (Differences in directory contents are not considered errors.)

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWesu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       cmp(1), diff(1), attributes(5), environ(5), largefile(5)

SunOS 5.11							    1 Feb 1995								 dircmp(1)