BASH scripting -- command saved as variable

bioinformatics_guy · 09-09-2008, 06:45 AM

Basically, I am trying to count how many files of a certain form are in a directory and using that number as a variable I use in a for loop.

The code is as follows:

...
end=${ls 1_* -1 | wc -l};
for ((i=1;i<=$end;i+=1)); do
...

./repeat.sh: line 28: ${ls 1_* -1 | wc -l}: bad substitution

is the error I am getting

What should I do?

colucix · 09-09-2008, 07:57 AM

In bash the syntax for command substitution is $(...). You used the wrong set of parentheses. See http://www.tldp.org/LDP/abs/html/commandsub.html for details.

ChrisAbela · 09-09-2008, 07:59 AM

end=$(ls 1_* -1 | wc -l);

You might want to consider using find instead of ls. It is much more versatile.

matthewg42 · 09-09-2008, 08:00 AM

Code:

variable_name=$(command)   # like this
variable_name=${command}   # not like this

bioinformatics_guy · 09-09-2008, 08:06 AM

Ah yes! I just caught that <--- definitely belong in the newbie forum.

Why would you pick find over ls?

matthewg42 · 09-09-2008, 08:21 AM

Quote:

Originally Posted by bioinformatics_guy

Ah yes! I just caught that <--- definitely belong in the newbie forum.

Why would you pick find over ls?

find has a load of options which ls does not. For example, you can select files which have been modified in the last so many days (using the -mtime option). You can build up some quite complicated logic with the -o -a and ! boolean operators.

For example, find can list all the files modified in the last 7 days whose name matches the pattern *.txt, but not starting with "account"

Code:

find . -name '*.txt' -a \! -name 'account*' -a -mtime -7

Have a read of the find manual page to get a better idea of all the possibilities.

bioinformatics_guy · 09-09-2008, 08:45 AM

Thats definitely a great command. I program mostly with perl and love its regexp but know almost nothing about its equivalent in bash. Whats a good reference book for shell scripting/unix commands? I've heard of Unix Powertools but not sure if thats exactly what I am looking for.

matthewg42 · 09-09-2008, 08:48 AM

If you have the infotext documentation installed, you might want to look at this command:

Code:

info coreutils

Here's a nice guide on the net: http://tldp.org/LDP/abs/html/

By the way, there's a nice tool which converts find commands into a perl script which has the same functionality: find2perl.

bioinformatics_guy · 09-09-2008, 09:29 AM

Great advice from all thank you! I actually found a command I was looking for in the coreutils documenation; sort. I'm sure I'll end up submitting a question on it but this has definitely started me off in the right direction.

i92guboj · 09-09-2008, 02:35 PM

The Advanced Bash Scripting Guide that matthewg42 mentioned is specially useful if you intend to learn serious bash scripting. Regardless of the name, it's suitable for all levels, starting from beginner.

chrism01 · 09-09-2008, 08:24 PM

There's also
http://tldp.org/LDP/Bash-Beginners-G...tml/index.html
http://rute.2038bug.com/index.html.gz