[SOLVED] How to use the % symbol in bash shell scripts

RedNeck-LQ · 08-11-2011, 09:31 PM

Hello,

I am curios about this special symbol I see in some bash scripts. The character is the % character.

excerpt from a script

youtube-dl http://www.youtube.com/watch?v=oef9ZnnhMzc -o "%(title)s.flv"

excerpt from a script
mv "$i" "${i%.vob}.avi"

I understand the last one, where the vob extension is replaced by the avi extention. In the instance the % character is used to delete characters from the right that matches a pattern of .vob

The "%(title)s.flv" is what I don't understand. How is the % character in this instance?

I've search google on how to use this character in shell scripts but couldn't find anything. All I find is basic shell scripting guides.

If anyone has any links or know-how on using this character in shell scripts, please explain it to me.

much obliged

paulsm4 · 08-11-2011, 09:54 PM

Hi -

I don't usually respond to something when I DON'T know the answer...

... but in this case, I think it's probably appropriate.

Because ...

"%" is *NOT* a "metacharacter" in the shell. For example, "$PATH" indicates "the value of the shell variable "PATH". The DOS equivalent is "%PATH%". But the shell metacharacter is "$", not "%". "%" is NOT a shell metacharacter.

Similarly, "%" isn't a shell wildcard, either. For example, you "ls *.txt" will find all .txt files. "ls "?.txt" will find all one-character-prefix .txt files. The shell's wildcards are more extensive and more sophisticated than DOS wildcards ... but "%" isn't a wildcard character, either.

Finally, "%" IS used to designate shell "jobs". But it DOESN'T look like that's what you're referring to.

Soooooooooo .... "%" is a metacharacter or wildcard character ... in something BESIDES the bash shell.

For example:

Code:

http://bashscripts.proboards.com/index.cgi?board=bash&action=print&thread=55

lynx --dump "http://www.youtube.com/view_play_list?p=465C6C735CEB7CBD" | grep "watch?" | awk '{print $2}' | cut -d\& -f1 | sort -u | while read link;do youtube-dl -o "%(title)s.flv" "$link";done
  <= Here, "youtube-dl" parses the "%", not the shell

EDIT:
Diantre posted the answer to your question below. The "%" in question are youtube-dl "Output Templates". They're documented here:

http://rg3.github.com/youtube-dl/documentation.html#d7

RedNeck-LQ · 08-11-2011, 10:42 PM

much obliged for the replay.

Quote:

Originally Posted by paulsm4

Soooooooooo .... "%" is a metacharacter or wildcard character ... in something BESIDES the bash shell.

So in other words, the youtube-dl app is using the % character as a wildcard and not the bash shell.

Still a bit confused...

BTW, do you know any links that explains this in more detailed.

if not, I appreciated the brief explanation you gave me.

tuxdev · 08-11-2011, 11:31 PM

I suspect the issue is that % is a magic char for URLs for escaping unicode glyphs.

Diantre · 08-12-2011, 12:08 AM

Quote:

Originally Posted by RedNeck-LQ

BTW, do you know any links that explains this in more detailed.

You can find documentation about Bash substring removal (${string%substring}) here. And documentation about youtube-dl output templates (%(NAME)s) in here.

Hope that helps.

RedNeck-LQ · 08-12-2011, 02:01 AM

Quote:

Originally Posted by Diantre

Hope that helps.

It greatly help, Diantre