bash scripting question

evo2 · 12-14-2009, 11:21 PM

Quote:

Originally Posted by ghostdog74

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.

You gave that script to someone else to use and you weren't even aware of the potential problems. Later you solved a potential problem (that you had not been aware of) that you never would have encountered if you had not used ls in the first place.

Quote:

What's the next unsafe scenario, if you may?

Ok, one more just for fun: spaces in file names:

Code:

touch a.txt
touch "c b.txt"
for f in $(ls *.txt) ; do echo "File is $f" ; done
for f in * ; do echo "File is $f" ; done

If you don't want to take my advice, that's fine.
Continue using ls.

Cheers,

Evo2.

PS. If you really want to discuss using ls in this fashion login to #linux at irc.freenode.net when GNU\Colossus is online: he'll have plenty to say on the topic.

ghostdog74 · 12-14-2009, 11:40 PM

Quote:

Originally Posted by evo2

You gave that script to someone else to use and you weren't even aware of the potential problems. Later you solved a potential problem (that you had not been aware of) that you never would have encountered if you had not used ls in the first place.

i didn't say i will give my script to someone else to use. Even if i did, the problem is already taken care of.

Quote:

Ok, one more just for fun: spaces in file names:

Code:

touch a.txt
touch "c b.txt"
for f in $(ls *.txt) ; do echo "File is $f" ; done
for f in * ; do echo "File is $f" ; done

i always advocate that if you want to parse file names, don't use for loop with ls like that, since its useless use of ls. Use shell expansion. If you really want to do that, change IFS

Code:

IFS=$'\n';for i in $(ls *); do echo "$i"; done

or use a while read loop.

however, this example doesn't apply here in this problem. I am asking, what other "unsafe" scenario for this case only. I am parsing ls -l for the owner and filename like OP wanted , and i have already taken care of that. What else?

evo2 · 12-14-2009, 11:47 PM

Quote:

Originally Posted by ghostdog74

i didn't say i will give my script to someone else to use. Even if i did, the problem is already taken care of.

That is exactly what you did right here. You gave the script to the OP and only later fixed.

Anyway, I'm getting sick of this. As I said, you are welcome to ignore my advice.

Evo2.

ghostdog74 · 12-14-2009, 11:51 PM

Quote:

Originally Posted by evo2

That is exactly what you did right here. You gave the script to the OP and only later fixed.

Anyway, I'm getting sick of this. As I said, you are welcome to ignore my advice.

Evo2.

conclusion: your script is only "unsafe" if you don't know what you are doing. Good bye

catkin · 12-15-2009, 12:38 AM

Quote:

Originally Posted by ghostdog74

What's the next unsafe scenario, if you may?

File names containing non-printable characters including backspace, linend etc. More fully explained in Greg's WIKI in Why you shouldn't parse the output of ls.

EDIT: similar discussion beginning with this LQ post.

ghostdog74 · 12-15-2009, 01:22 AM

yes, thank you. That's one point to keep in mind.
To get back to topic, I only want to know what's "unsafe" for OP's problem. If i may reiterate, he just wants to get .bash_history (which no newlines or special characters in file name) and parsing ls to get the owner ( and not filename ) is alright and not "unsafe". If i do want to parse file names as well and i know it possible that my filenames can contain other chars or newlines, I won't recommend parsing ls either.

catkin · 12-15-2009, 01:52 AM

Quote:

Originally Posted by ghostdog74

I only want to know what's "unsafe" for OP's problem.

As you point out, .bash_history does not contain any unprintable characters and I do not know of any versions of ls that do not ordinarily put the user name in space-separated field 3 so your code is safe in all known circumstances -- except ls could be (and often is) an alias

Code:

c:/tmp$ alias ls='ls -Di'
c:/tmp$ ls -l
  total 8
  212610 srwxr-xr-x 1 c users    0 Dec 15 11:37 OSL_PIPE_1000_SingleOfficeIPC_f24b151f1666ce0a2d65526a3964194
  210604 drwx------ 2 c users 4096 Dec 15 11:35 ssh-CciYjZ3847
  212654 drwxr-xr-x 2 c users 4096 Dec 15 11:53 sv5pd.tmp
//DIRED// 58 119 168 182 231 240
//DIRED-OPTIONS// --quoting-style=literal
c:/tmp$ \ls -l
total 8
srwxr-xr-x 1 c users    0 Dec 15 11:37 OSL_PIPE_1000_SingleOfficeIPC_f24b151f1666ce0a2d65526a3964194
drwx------ 2 c users 4096 Dec 15 11:35 ssh-CciYjZ3847
drwxr-xr-x 2 c users 4096 Dec 15 11:53 sv5pd.tmp

firehak · 12-15-2009, 04:54 AM

Thanks to everyone who replied. This was my final result and it works perfectly and now I can use it for class today.

Code:

#!/bin/bash

echo "Please note that if you do not have sudo priviliges, you only copy your own .bash_history."
echo "Please enter your user name: "
read admin

mkdir -pv /home/$admin/history

for f in /home/*/.bash_history ; do
  owner=$(stat --print %U $f)
  cp -p $f /home/$admin/history/${owner}.history && chown $admin /home/$admin/history/*
done

evo2 · 12-15-2009, 05:02 AM

Quote:

Originally Posted by firehak

Thanks to everyone who replied. This was my final result and it works perfectly and now I can use it for class today.

Cool.

Just a couple of things. I'd probably put 'set -x' on the first line so that the script will exit if there are any errors. I'd also either move
the

Code:

chown $admin /home/$admin/history/*

to be just after the loop, or the other option is change it to

Code:

chown $admin /home/$admin/history/${owner}.history

The other thing I'm a bit confused about is that the user running the script, enters their username... the shell can get that from the $USER variable.. and that user will own the cp of the file anyway.

Cheers,

Evo2.

ghostdog74 · 12-15-2009, 05:15 AM

Quote:

Originally Posted by firehak

Thanks to everyone who replied. This was my final result and it works perfectly

for a more efficient approach using stat, see post #6.

firehak · 12-15-2009, 06:38 AM

Quote:

Originally Posted by evo2

Cool.

Just a couple of things. I'd probably put 'set -x' on the first line so that the script will exit if there are any errors. I'd also either move
the

Code:

chown $admin /home/$admin/history/*

to be just after the loop, or the other option is change it to

Code:

chown $admin /home/$admin/history/${owner}.history

The other thing I'm a bit confused about is that the user running the script, enters their username... the shell can get that from the $USER variable.. and that user will own the cp of the file anyway.

Cheers,

Evo2.

I'll try that. I used $USER at first, but when running sudo it took user root as the $USER. And for some reason running without sudo at school lets me see permission denied for every user, but running with sudo only copied 1 user, administrator, my teacher, and root.

EDIT:
And I still can't copy everyone. I get 2 people I'm actually supposed to copy, then administrator and root.

EDIT..again..
Sorry for the confusion. It did work, my teacher just told me he accidentally copied the same .bash_history to everyones folder.

firehak · 12-16-2009, 09:33 AM

Hey, if it helps anyone, I was bored in class and modified it further. It now combines all the history files into one large file, with "username"'s history above their history section and I added the lastlog command to the end and saved results to a file called login_info

Code:

#!/bin/bash

echo "Please note that if you do not have sudo priviliges, you only copy
your own .bash_history."
echo "Please enter your user name: "
read admin

mkdir -pv /home/$admin/history
rm -Rf /home/$admin/history/*


for f in /home/*/.bash_history ; do
  owner=$(stat --print %U $f)
  cp -p $f /home/$admin/history/${owner}.history
  sed -i "1i-----------------------------------\n"${owner}"'s history\n-----------------------------------\n" /home/$admin/history/${owner}.history
  chown $admin /home/$admin/history/*
done

lastlog >> /home/$admin/history/login_info

cat /home/$admin/history/*.history >> /home/$admin/history/history
rm /home/$admin/history/*.history

chrism01 · 12-16-2009, 05:48 PM

FYI: priviliges => privileges