Shell Programming and Scripting

hi,

I have been trying to acheive the following task for a while now, but failed.. Need help, experts please help!

This is what I am trying to do:
- I am writing to a flat file the name of the source to be copied and the destination path as to where it is to be copied to.
Sample flat file:
Abc.scr $DESTN_PATH/test
Def.scr $DESTN_PATH/new

- I am reading the source name from this file from a shell script and replacing in the cp command. For example in the file above filename=abc.scr destn= $DESTN_PATH/test
So in shell script I am executing: cp $filename $destn

The issue I am facing here is that in the cp command the value of the environment variable $DESTN_PATH is not replaced, hence the file is copied correctly.

Please help guys!

there can be many scenarios where something is going wrong

export the DESTN_PATH variable. (it shouldn't contain / at last of the path, otherwise you will two // in your output expression)

Code:

correct ex - export DESTN_PATH=/fs/dir1/dir2
wrong ex - export DESTN_PATH=/fs/dir1/dir2/

make sure the assignment doesn't contain any space on both side of '='

it should work else post your sample code here.

That doesn't actually matter. If you can name any extant UNIX system which doesn't do the right thing when given two /'s, I'll be quite surprised.

If i remember I faced it sometimes back. Not sure if it was exact same but related to it.

First off, if this:

Code:

filename=abc.scr destn= $DESTN_PATH/test

is what you really have in your script then it will not work because of the superfluous space between "=" and "$". If it was just a copy error consider this point to be moot.

Without regard to this, if i have understood you correctly:

You have a file like this:

Code:

one.file    $DEST/new.filename
other.file   $DEST/other.newname

and you read it something like this:

Code:

DEST=/some/where
SRC=""
TGT=""

while read SRC TGT ; do
     cp $SRC $TGT
done < file

and you expect the "$DEST" to be expanded by the shell? Well, this won't work, because of the evaluation process of the shell. When it evaluates "$TGT" all the variable evaluation is done and to further evaluate the resulting "$DEST/..." would require the variable substitution process to restart. I have described this in detail in this thread.

The solution is the same as in the other thread and for the same reasons: use eval.

Still, this is a unsatisfying solution, because it is inherently problematic. You might want to create a more robust solution like this:

The first non-comment line of your input file shall be of the form "DEST=/some/path". Multiple lines of this form are allowed and change the value of "$DEST" until the next occurrence of such a line. This is parsed by your script and used to set the value of DEST:

Sample of input file:

Code:

# This is a possible input file
DEST=/some/where
first.file first.file.new

# now we change the DEST value
DEST=/else/where
second.file second.file.new
third.file third.file.new

The expected output from such an input would be like this:

Code:

cp first.file /some/where/first.file.new
cp second.file /else/where/second.file.new
cp third.file /else/where/third.file.new

Here is a sketch of such a script (replace "<spc>" and "<tab>" with the respective literal characters):

Code:

#!/bin/ksh

INFILE="$1"
DEST=""
SRC=""
TGT=""

# the sed is only to clean out comments, leading and trailing blanks and empty lines
sed 's/#.*$//
     s/^[<spc><tab>][<spc><tab>]*//
     s/[<spc><tab>][<spc><tab>]*$//
     /^$/d' $INFILE |\
while read SRC TGT ; do
     if [ "${SRC%=*}" = "DEST" ] ; then
          DEST="${SRC#=}"
     else
          if [ -z "$DEST" ] ; then
               print -u2 - "Error in input file, no \"DEST=\" clause."
               exit 2
          fi
          if [ ! -r "$SRC" -o -w "$DEST" ] ; then
               print -u2 - "Error: $SRC not readable or $DEST not writable."
               exit 1
          fi
          print - "cp $SRC $DEST/$TGT"     # remove the print if the result is as expected
     fi
done

exit 0

I hope this helps.

bakunin

Bakunin, thank you for a great answer, but this solution isnt something I want to use, the reason being that this would necessitate to know all the environment variable names that are going to be used. Any new variable added would require an update to the main script..

I will try out this option at work tomorrow, but what would really help me is something which would replace any environment variable with its value without the check and replace in the script.

To be honest i don't quite get it. Actually this is the case in your proposed solution, not in mine: just because i denominate it "DEST" in the file as well as in the variables name doesn't mean they have to be equal: try it out and rename the variable "DEST" throughout the script and you will see that it still works as expected.

I have already told you how this works: use "eval" like i explained at length in the link i gave. But be warned: this works ONLY, if the variable you use in the configuration file is predefined in the script with the exact name to match. In fact this behavior - every change to the environment will make a script change necessary - is true for your solution, because you define the value to which the variable should expand only in the script, not in the configuration file. As you can have many configuration files, but only need one script to run them, i think my solution will be more flexible than yours, but anyway, do as you like.

But maybe i got your requirement wrong (if so: please explain in detail what you want to do - the thing with "any environment variable" is obviously not part of the "i write a script to copy files" requirement, because it wouldn't be necessary for that), so please post your script and the intended input file alonw with its expected output or effect. This might help to understand better what you want to do.

I hope this helps.

bakunin