bash scripting question

firehak · 12-14-2009, 08:27 PM

I'm trying to copy the .bash_history file out of each users home directory and paste it into a directory in my teachers home folder. Is there any way I could can return just the owner of a file? If I could get just that output I know I could easily write the rest of the script on my own.

ghostdog74 · 12-14-2009, 08:32 PM

Code:

set -- $(ls -l /path/to/bash_history)
echo "Owner is: $3"

firehak · 12-14-2009, 08:42 PM

Thank you so much, I've been looking around and trying various ways all day.

EDIT:
Hm. I still can't get it right. Here's my script:

Code:

#! /bin/bash

set -- $(ls -l /home/*/.bash_history)
cp /home/*/.bash_history /home/stephan/$3.history

And here is my output:

Quote:

cp: target `/home/stephan/lfs.history' is not a directory

So I apparently need more help than I thought. I'm assuming it's also only grabbing the first value found by the wildcard, but I'm trying to grab every users history. I have a linux from scratch user and my user here, but at school there is about 20 on the computer and he want's to make sure the juniors are actually doing what they're supposed to.

evo2 · 12-14-2009, 09:40 PM

In practice it is better not to parse the output of ls. I this case you can uses the stat command.
You can also use a loop, copy the files one, by one. The following should work, but is *untested*

Code:

#!/bin/bash
for f in /home/*/.bash_history ; do
  owner=$(stat --print %U $f)
  cp $f /home/stephan/${owner}.history
done

Cheers,

Evo2.

firehak · 12-14-2009, 09:46 PM

Quote:

Originally Posted by evo2

In practice it is better not to parse the output of ls. I this case you can uses the stat command.
You can also use a loop, copy the files one, by one. The following should work, but is *untested*

Code:

#!/bin/bash
for f in /home/*/.bash_history ; do
  owner=$(stat --print %U $f)
  cp $f /home/stephan/${owner}.history
done

Cheers,

Evo2.

Thank you so much, I just tested and it worked perfectly. I just need to add a "chown" or "chmod" to make it viewable for the myself and the other 2 admins now. You saved me a lot of time =D

ghostdog74 · 12-14-2009, 09:52 PM

Quote:

Originally Posted by firehak

So I apparently need more help than I thought. I'm assuming it's also only grabbing the first value found by the wildcard, but I'm trying to grab every users history. I have a linux from scratch user and my user here, but at school there is about 20 on the computer and he want's to make sure the juniors are actually doing what they're supposed to.

that piece of code is for only 1 file. to do it for many

Code:

ls -l /home/*/.bash_history | while read -r  line
do 
   set -- $line
   echo "owner: $3, file: ${@:8}"
   # cp your stuff
done

similarly, if you want to use stat like this for one invocation.

Code:

stat -c "%U:%n" /home/*/.bash_history| while IFS=":" read -r owner filename
do
  cp "$filename" "/home/stephane/${owner}.history"
done

be careful of overwriting files with the same owner though.

lastly, for your experimentation

Code:

stat -c "cp %n /home/stephen/%U.history"

evo2 · 12-14-2009, 10:01 PM

Quote:

Originally Posted by ghostdog74

that piece of code is for only 1 file. to do it for many

Code:

ls -l /home/*/.bash_history | while read -r  line
do 
   set -- $line
   echo "owner: $3, file: ${@:8}"
   # cp your stuff
done

Seriously, it is a bad idea to try to parse the output of "ls -l". One reason in this case is that the date format can be different depending on the users environment and as such the field number, in $line for the file name could change. ls should be used for human readable output, stat is a better option for parsing in scripts.

Evo2.

ghostdog74 · 12-14-2009, 10:18 PM

Quote:

Originally Posted by evo2

Seriously, it is a bad idea to try to parse the output of "ls -l". One reason in this case is that the date format can be different depending on the users environment and as such the field number, in $line for the file name could change. ls should be used for human readable output, stat is a better option for parsing in scripts.

Evo2.

true, it good to use stat in general since stat has many more features, but not for this case and other simple cases. ls -l uses the same stat library as "stat" command. if i am worried about time format, there are various ways to go around it. I can get rid of the date and time portion.

Code:

ls -lg --time-style="+" |while read -r line
do
    set -- $line
    echo "owner: $3, filename: ${@:5}"
done

therefore, the notion of "bad idea to parse ls output" is not true for this case

anyway, i have also provided stat suggestion so its up to OP

ghostdog74 · 12-14-2009, 10:19 PM

Quote:

Originally Posted by evo2

Code:

#!/bin/bash
for f in /home/*/.bash_history ; do
  owner=$(stat --print %U $f)
  cp $f /home/stephan/${owner}.history
done

why not let stat do the file parsing instead of calling stat in the for loop for each file?

evo2 · 12-14-2009, 10:30 PM

Quote:

further, if i am worried about time format, there are various ways to go around it. I can get rid of the date and time portion.

Sure, you can pass all sorts of options to ls, but the point is that it is both safer and easier, to not use it at all.

Quote:

anyway, i have also provided stat suggestion so its up to OP

Yeah, you seemed to be editing your post while I was writing mine.

Evo2.

ghostdog74 · 12-14-2009, 10:38 PM

Quote:

Originally Posted by evo2

Sure, you can pass all sorts of options to ls, but the point is that it is both safer and easier, to not use it at all.

if this principle applies to you, that's fine. But not all adheres to that notion.

evo2 · 12-14-2009, 10:45 PM

Quote:

Originally Posted by ghostdog74

if this principle applies to you, that's fine. But not all adheres to that notion.

Sure, safety and ease of use are not what everyone is looking for.

Bye,

Evo2.

ghostdog74 · 12-14-2009, 10:49 PM

Quote:

Originally Posted by evo2

Sure, safety and ease of use are not what everyone is
.

well, i am curious. What's so "unsafe" about parsing ls -l output, in THIS case, since I have shown how to get owner and filename correctly. mind giving an example?

Also "ease of use" is subjective, so i am not talking about it.

evo2 · 12-14-2009, 11:00 PM

Quote:

Originally Posted by ghostdog74

well, i am curious. What's so "unsafe" about parsing ls -l output, in THIS case, since I have shown how to get owner and filename correctly. mind giving an example?

I did. I told you about the time format issue. You then modified your script so that the date of the file was not not printed. This is exactly the sort or problem you will get when trying to parse the output of ls in scripts.

Quote:

Also "ease of use" is subjective, so i am not talking about it.

Fine by by me.

Evo2.

ghostdog74 · 12-14-2009, 11:05 PM

Quote:

Originally Posted by evo2

I did. I told you about the time format issue. You then modified your script so that the date of the file was not not printed. This is exactly the sort or problem you will get when trying to parse the output of ls in scripts.

If i know my time format and parse according to that, its not a problem. If i am going to run my script in various linux machines with different time format, then i can get rid of the timestamp and it will work as well... ok, so one aspect solved. What's the next unsafe scenario, if you may?