[SOLVED] how to direct stdout into a file

hanansela · 10-03-2011, 06:07 AM

Hello
I have gust started to play with Linux scripts. i know that for simple commands i can add ">outfile" or ">>outfile" to direct stdout into outfile. However, i could not figure how to do that with a bit more complex line like this:

Code:

for k in $(ls *.jpg); do b=`basename ${k%.jpg}`; convert $b.jpg -colors 265 -format "%c" histogram:info: ; done

This gives an output of many lines of data describing the histogram of colors of a list of jpg files

Any help would be appreciated. Please be gentle and either give examples or detailed explanation. I am a newbie.
Thank you

colucix · 10-03-2011, 06:39 AM

Exactly the same: you can add >> outfile after the convert command or even after the entire for loop:

Code:

for k in $(ls *.jpg)
do
  b=`basename ${k%.jpg}`
  convert $b.jpg -colors 265 -format "%c" histogram:info:
done >> outfile

If you want a different output for each processed file, use the loop variable or the $b variable:

Code:

for k in $(ls *.jpg)
do
  b=`basename ${k%.jpg}`
  convert $b.jpg -colors 265 -format "%c" histogram:info: > $b.out
done

hanansela · 10-03-2011, 07:13 AM

Thank you colucix for the replay
I did what you suggested and it works fine. The >> appending signal is what i needed since it collects all the results together.

David the H. · 10-04-2011, 12:56 AM

Commands can also be grouped together with "{..}".

Code:

{ commandA && commandB || loop C ; whatever ;} > file

Notice that when everything is on a single line the final bracket needs to be separated with a semicolon.

In addition, you can also use "(..)" to run everything in a subshell, but you should really only use that when you actually need a subshell.

PS: $(..) is highly recommended over `..`

Edit: Actually, instead of basename, why not simply use another parameter substitution? Doing such things in-shell is nearly always more efficient than calling an external process.

Code:

b=`basename ${k%.jpg}`  #b=$(basename "${k%.jpg}") would be better

#change to:

b=${k%.jpg}
b=${b##*/}