UNIX for Dummies Questions & Answers

Hi.

I use an alias, "homeperm" as shorthand for curl -o. Since most of what I download via cUrl is graphic image files -- jpeg files -- I'd like to be able to change this alias to a script, or use it to invoke a function, which will not only download the file but date-stamp it using Exiv2 in either (or both) the IPTC or EXIF annotation "blocks". This would save me the hassle of going back and manually entering this information after reading the mod date for file X or Y in my file manager.

if anyone is familiar with the "curl -o" command, and I suppose not a few people are, then you know that its syntax is [command][your-file-name][source-URL]. Where I'm drawing a blank in turning this alias into something fancier is: I'm not sure, having neither seen it done nor done it myself in the past, how to write a script or function that will follow this same syntax.

I've done some simple scripts that prompt for input using the echo and read commands, but what I'm looking for is a way to enter the [your-file-name] and [source-URL] parts on the same line with the "homeperm," which is how the alias works and is very much what I've grown accustomed to.

Is it possible in BASH to get the second and third parts of a string from stdin passed, just as a f'r'instance, as variable values that can be handled by a function or script like this? If so, how would one go about it?

Or is it necessary to already have a subshell running before such a thing could be done?

I'm sorry I can't offer any "crappy candidate code" to show what I mean, but if anyone needs part or all of this idea explained any more clearly, then please ask: I'll do my best.

Hoping someone can help me with this.

BZT

I dont get what you mean by "enter the [your-file-name] and [source-URL] parts on the same line with the "homeperm"

The alias works like this:

Code:

homeperm bigger-than-life-xhd.jpg http://www.wd.com/store/drives/excalibur-premium-26tb-portable-sata-hd.jpg

(just something off the top of my head)

You'll notice that the name I'm giving the file and it's source URL are on the same line as the alias. I'm positive that this is because aliases, by definition, often substitute one word for two, or are used in place of particular commands that are easily confused with others the same binary might employ. cUrl also has, on its man page, a curl -O command -- the original reason for creating this alias was that I couldn't remember which "o" did what.

Does this explain it adequately?

BZT

---------- Post updated at 14:02 ---------- Previous update was at 13:57 ----------

I know an alias invoking a function or script can be made to perform a simple task on a local file. I have another alias, ditto, that starts a script called mditto, the code of which looks like this:

Code:

	d=$(exiv2 -g Iptc.Application2.FixtureId -Pv $1 2>/dev/null)
	if [[ "d" != "" ]]; then
		exiv2 -M"set Iptc.Application2.ObjectName $d" -k $1
		echo -e "RUBBERSTAMP: $1; '$d' to ObjectName field"
		echo -e "Thank Irfan for me next time you see him!"
	else
		echo -ne "Ditto what? There's no Fixture ID data in $1."
		echo -ne "I'll pass on this one thanks."
	fi

"$1" is the variable (placeholder?) for the file to be worked on. If I had a "$1" with a value of ...I suppose I could use 'cut' or a string builtin to break it into two variables at the space, give those values to cUrl, stat (for) the date on "bigger-than-life-xhd.jpg" and pass the mod date from that to Exiv2 to annotate the file.

Does it sound like I'm on the right track? I'll try some code in a short while, test it, and if I run into a wall I'll be back round to ask where I'm coming up short.

BZT

If you want to use parameters, a function would be better than an alias. Not all shells have them but bash definitely does. You can use them like little callable scripts you put in your .bashrc

Code:

function homeperm
{
        local LOCALFILE="$1"
        local URL="$2"

        do_stuff_with_parameters
}

...and you'd just run it as homeperm parameter1 parameter2

And no, you never need to use 'cut' to do something as simple as that, the read command can do a lot for you:

Code:

$ read A B <<< "c d"
$ echo $A
c
$ echo $B
d
$

You can also split on something other than whitespace:

Code:

$ IFS="|" read A B <<< "c d|e"
$ echo $A
c d
$ echo $B
e
$

It's much more efficient than calling cut since read's a builtin and always a builtin.

I appreciate the suggestions. Likely as not I'll be coming up with some scripts very much like this one in the near future, so I'll keep this thread bookmarked.

What I failed to mention is, while I write the filenames I want into the "homeperm" or "curl -o" command, I usually paste in the source URLs from the clipboard of whatever OS I happen to be using. This gave me a bit of a headache just using $1 as input from the line, as curl only saw the filename as I typed it and didn't have anything for a URL. It wasn't until I echo'd what curl was getting for input that I gleaned what I was doing wrong.

Then I thought, "If there's a $1, shouldn't there be a $2? Single spaces are seen by BASH as a break, if not a delimiter, aren't they?" So I tried this line near the top of the script:

Code:

echo -e "$1 $2"

and invoked the script (with a standby alias, "homecourt"). Sure enough, the URL printed to stdout right after the filename as sure as dinner follows lunch. cUrl downloaded the file, and the code I had written to annotate the dates ran smooth as melted butter.

Here's the final script.

Code:

#!/bin/bash
actiondate=$(/usr/bin/date)
echo -e "$1 $2 $actiondate"
clockdate=$(date '+%d %B, %Y.')
myfile=$1
myurl=$2
curl -o $myfile $myurl
fulldate=$(stat -c %y $myfile)
shortdate=${fulldate%.*}
exiv2 -kM"set Exif.Image.DateTimeOriginal Ascii $shortdate" $myfile
exiv2 -kM"set Iptc.Application2.SpecialInstructions String Downloaded $clockdate" $myfile
exiv2 -kM"set Exif.Image.DocumentName Ascii $myurl" $myfile
echo -ne "File $myfile downloaded and annotated with date and time.\n\n"

Thanks again for the suggestions.

BZT