Argument list with bash script

[daviddoria]

I want to loop through the arguments in a bash script (ie if I call
./MyScript *.txt
in a folder with files: a.txt b.txt c.txt
I want to operate on each of those files.)

I know the arguments are $1, $2, etc - but how do you construct a variable name like that - ie

#!/bin/bash
echo number of arguments is $#

for i in `seq 1 $#`; do
    echo argument ${i}: `$i` #this last part is the problem
done;

See what I'm trying to do? Is this how this should be approached?

Thanks,
Dave

[daviddoria]

Comment:
I know about

for i in $*; do
echo $i
done;

But then I don't have the argument's index.

Dave

[RupertPupkin]

You could do this:

#!/bin/bash
args=("$@")
for ((i=0; i < $#; i++)) {
   echo "argument $((i+1)): ${args[$i]}"
}

[daviddoria]

Good idea.

[sideways]

There are a couple of subtle but important bits in RupertPupkin's very nice and compact script

args=("$@") is superior to the sometimes seen args=($@) since the former will not create separate array elements if any of the args have spaces in them (so actually this is a pretty cool way to iterate through a directory with filenames containing spaces)

Note that the array index starts at zero, but the command line args start at one, which is why the test in the loop is 'i < $#' not 'i <= $#' and the argument index is offset by 1 in the output.

[daviddoria]

Who would ever put spaces in file names!!?? That should be punishable by death

[sideways]

I know you're joking, but most media/music directories are full of spaced filenames.

[scottro]

Spaces in filenames are quite frequent--not only in media files, but whenever users name files. Microsoft and Apple both accept spaces and have no trouble handling them, so users will make use of that.

In my past job, though, I remember an incident where there were several seemingly identically named files. It turned out that a user had at times, written the file name and hit space rather than enter, so there were files like image.jpg and image.jpg with a space after the jpg.

(Eventually, I ran cat -e on the directory, which puts a $ at the end of each line, so I could see that there were several like image.jpg$ and image.jpg $.)

Point being, especially if you're working professionally, that whether it's a bad idea or not, you may often run into it.