Bash: Pattern matchin - how to do matching on a variable?

jhwilliams · 12-08-2009, 07:30 PM

Quote:

Originally Posted by chrism01

SQADude is saying that

ls -l

always produces one 'record' per file per line of output, and anything(!) after the date/timestamp in each rec is the filename, with or without spaces in it.

So the point is just that multiple filenames don't show up in rows? Well, I suppose as someone else noted above, ls -1 (not -l) would avoid that.

chrism01 · 12-08-2009, 07:46 PM

I agree. The OP should clarify whether he needs other info as well.

SQADude · 12-08-2009, 08:02 PM

Quote:

Originally Posted by jhwilliams

So the point is just that multiple filenames don't show up in rows? Well, I suppose as someone else noted above, ls -1 (not -l) would avoid that.

Using -1tr (that's a '1', not "l") would fix my problem. All I would have to do is to take the last row and the last row would be the filename.

However, for academic sake (I'm trying to learn sed/regex), how would I do this?

Do an "ls -ltr" (not a 1 but an l) on a file and then extract its filename?

For example, let's just say that there is only one file called "foo space" in this directory. If I do an "ls -ltr foo*", I get this output:

-rw-rw-rw- 1 root root 1001 Dec 8 17:58 foo space

I want to get "foo space" in a variable called fileName.

In perl, I could do this:

Code:

my $outPut = `ls -ltr foo*`;

$outPut =~ /:..\ (.+)$/;
my $fileName = $1;
print '$fileName is: ', "$fileName \n";

BTW, the Perl code above works. I tried it.

How would I do that in BASH?

jhwilliams · 12-08-2009, 08:23 PM

In the case you have given, this would be sufficient:

Code:

filename=foo*

If there is no filename matching the glob foo*, then $filename will contain the literal string 'foo*'. So you might want to check to see that the glob has actually matched a file:

Code:

[ -f "$filename" ] || echo "$filename" is not a file.

If you are expecting multiple matches on a glob (as is probably more reasonable) you might combine the above approach with the Bash array capability.

Code:

# Get an array, with one filename per entry.
filenames=(foo*)

# Either you have 0 filenames, or 1..n filenames.
# Check the first entry of the array to see if it is a filename.
# If not, error out.
[ -f "${filenames[0]}" ] || echo "no matches" && exit 1

# Do whatever it is you have to do -- perhaps with a for loop.
for item in "${filenames[@]}"; do 
    echo "$item";
done

ghostdog74 · 12-08-2009, 09:44 PM

Quote:

Originally Posted by SQADude

In perl, I could do this:

Code:

my $outPut = `ls -ltr foo*`;

$outPut =~ /:..\ (.+)$/;
my $fileName = $1;
print '$fileName is: ', "$fileName \n";

BTW, the Perl code above works. I tried it.

How would I do that in BASH?

what is wrong with using this ?:

Code:

for file in foo*
do
 echo "do everything in this loop" 
 # if you want to check if its a file
 if [ -f "$file" ] ;then
    echo "$file"
 fi
done

quote your variables when you are using it, so that spaces are taken care of.

catkin · 12-09-2009, 01:03 AM

Quote:

Originally Posted by ghostdog74

what is wrong with using this ?:

If there are no files matching foo* then the shell will expand foo* to exactly that, foo*, unless shopt nullglob is set. It is unset (displayed as "off" by the shopt command) by default on Slackware 13.0.

catkin · 12-09-2009, 01:11 AM

Quote:

Originally Posted by jhwilliams

Well, the issue of having an \n embedded in a filename is not really a legitimate concern. Anyone who were to do this would surely be fired, and their files would be renamed by their replacement.

Wow! [irony]Nice organsation.[/irony] Typically files with "pathological" characters in their names are not created by people but by software bugs or file system corruption. There are quite a few threads on LQ posted by people needing to delete or rename such files -- and they usually have no idea how those file names were created.

ghostdog74 · 12-09-2009, 01:36 AM

Quote:

Originally Posted by catkin

If there are no files matching foo* then the shell will expand foo* to exactly that, foo*, unless shopt nullglob is set. It is unset (displayed as "off" by the shopt command) by default on Slackware 13.0.

yes that's right. nullglob should be set if that's the case (or specifically use -f to test for file existence). However that's not the point, since OP is using ls with wildcard expansion produces error as well.

Code:

for file in foo*
do
 if [ -f "$file" ];then
   echo "found..continue processing here"
 fi
done

catkin · 12-09-2009, 01:47 AM

Quote:

Originally Posted by ghostdog74

yes that's right. nullglob should be set if that's the case (or specifically use -f to test for file existence).

Sorry -- I missed that; the -f test handles it

.