You can use variable variables inside the loop so you don’t have to repeat each if block.

To see how they work, try this:
VAR1=abc
abc=123
echo ${!VAR1}

Inside your while read loop you could do something like this:

fred=”"
for VAR in col1 col2 col3 col4; do
if [ -n "${!VAR} ] ; then
fred=$fred”${!VAR}”
fi
done

I have the following code to read in a file an process accordingly :

#/tmp/test.txt looks like this :
# 0-1|0-2|0-3|0-4
# 1-1||1-3|1-4
# |2-2|2-3|2-4
# 3-1|3-2||3-4

FILENAME=$1; #input filename
OIFS=$IFS;
IFS=’|';

while read col1 col2 col3 col4
do
if [ -n "$col1" ]; then
fred=”col1 = ‘$col1′, “;
else
fred=”";
fi
if [ -n "$col2" ]; then
fred=$fred”col2 = ‘$col2′, “;
else
fred=$fred;
fi
if [ -n "$col3" ]; then
fred=$fred”col3 = ‘$col3′, “;
else
fred=$fred;
fi
if [ -n "$col4" ]; then
fred=$fred”col4 = ‘$col4′”;
else
fred=$fred;
fi
echo $fred;
done <$FILENAME

#the output looks like this
col1 = ‘0-1′, col2 = ‘0-2′, col3 = ‘0-3′, col4 = ‘0-4′
col1 = ‘1-1′, col3 = ‘1-3′, col4 = ‘1-4′
col2 = ‘2-2′, col3 = ‘2-3′, col4 = ‘2-4′
col1 = ‘3-1′, col2 = ‘3-2′, col4 = ‘3-4′

I want to know - can I substitute ‘col1 - col4′ for a variable, since there is about 40 fields per line on the “real” file and to do more or less the same validation repetitively seems pointless.

any suggestions would be appreciated.

thanks

http://unstableme.blogspot.com/

Thanks for the tips on quoting and nulls!

You can work around the spaces problem very easily in xargs, don’t write it off so soon.

$ cat files.lst
File with spaces.txt
file2.txt

$ cat files.lst |xargs -i rm -v “{}”
removed `File with spaces.txt’
removed `file2.txt’

$cat files.lst |xargs -i echo {}
File with spaces.txt
file2.txt

Using the find command from findutils, you can also specify -print0 to print NUL characters for spaces instead of whitespace. Xargs can them interpret the whitespace via the -0 (that’s a zero) flag. find -print0 and xargs -0 should never fail because UNIX paths won’t contain NULs.

g_m.

The point isn’t to replace cat, or get find to output the files. That is just a simple example.

The intent is to demonstrate reading something line by line and acting upon it. echo can be replaced with any other command, or a series of commands and maybe some logic.

# find . -name ‘*jpg’ | while read pic ; do
convert ${pic} ${pic}.png
mv ${pic}.png /some/new/dir
done

Or you could pull pic apart and, replace the jpg with png properly, and maybe resize if it’s over X bytes, etc.

I like to escape my shell vars so I don’t get into problems with concatination. It’s a personal preference and while other methods work, this is what I like. That way I don’t accidently try something like “$PATHnewdir” which isn’t the same as “${PATH}newdir”

Thank you for the response. Your example worked just great. Thank you very much! Now I need to pass the file generated by redirecting into a file, i.e., the echo $x1 $x2 $x3 $x4 ; done > ids2.txt and passing that as an argument into another bash script. Thanks again