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Script to Change file permissions

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Script to Change file permissions

 
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  #1
Jun 23rd, 2009
Hi

I am new to unix and want to learn shell scripting.
Right now I am use cygwin for windows but sooner I will switch to ubantu.

So when I wrote my first script (just copied from the book I was reading), I came to know I have to give execute permission to the script file.

So now I want to create a script which will take the file as input and will just change the permissions such that It wont effect read/write permission but only grant the execute permissions.

So I tried to write something like this (code mixed with psuedocode is written below)

Shell Scripting Syntax (Toggle Plain Text) 
  1. #GrantExPer
  2. #Usage: GrantExPer <filename>
  3.  
  4. str1='ls -la '  #first string
  5. str2=$1  # second string contains file name
  6. echo $str2   # this works
  7. comm1=$str1 $str2  #command1 by concatenating string 1 and string 2, this doesn't work for me
  8. $comm1 #execute command1
  9. var1=$1 #get output of the above command in some var1
  10. #find out current permissions using var1 and calculate some integer $newPermission (which contains new permissions)
  11. chmod $newPermission $str2 #str2 still contains file name I think
  12.  

Please guide me for:
1. How to make a right command. I tried it by concatenate 2 strings. (line 4-7)
2. Then how to execute it. (line 8)
3. Is there any command which shows me file permissions in a number format like 644 rather than -rw-r--r--. To me number format seems easier to manipulate.


Thanks
When I was in 10th i thought I knew all the maths, when I came to graduate level, I thought there is something I didn't know about, and when I completed my PhD, i knew that I don't know anything about maths.
life's like math
oh btw... I haven't done PhD
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Re: Script to Change file permissions

 
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  #2
Jun 23rd, 2009
1.
bash Syntax (Toggle Plain Text) 
  1. #!/bin/bash
  2. if [ "$1" = "" ]; then
  3.   echo "usage: $0 [filename]"
  4.   exit 1
  5. fi
  6.  
  7. if ! test -f $1
  8. then
  9.   echo "Invalid file name"
  10.   exit 1
  11. fi
  12.  
  13. chmod u+x $1

2. Put the above code in grant.sh, chmod a+x grant.sh, ./grant.sh

3.
You can use 'stat' to get octal permissions. There are a number of approaches outlined at http://www.lockergnome.com/linux/200...c-permissions/ on getting octal perms.
Scott Knake
Custom Software Development
Apex Software, Inc.
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Re: Script to Change file permissions

 
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  #3
Jun 23rd, 2009
thanks...

other than error handling there is only one line...
chmod u+x $1
and that's how we learn... I spent more than 1 hour on this....

Thank you very much...

but i still want to know: how to concatenate two strings to make a command and then how to execute that command. Or do we need to always find a workaround.
Last edited by grvs; Jun 23rd, 2009 at 10:41 am.
When I was in 10th i thought I knew all the maths, when I came to graduate level, I thought there is something I didn't know about, and when I completed my PhD, i knew that I don't know anything about maths.
life's like math
oh btw... I haven't done PhD
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Re: Script to Change file permissions

 
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  #4
Jun 23rd, 2009
Shell Scripting Syntax (Toggle Plain Text) 
  1. sk@sk:~$ STR1='i'
  2. sk@sk:~$ STR2='d'
  3. sk@sk:~$ "${STR1}${STR2}"
  4. uid=1000(sk) gid=110(wheel) groups=110(wheel),4(adm),43(utmp)

You can also use `` ticks to execute commands from output:
Shell Scripting Syntax (Toggle Plain Text) 
  1. sk@sk:~$ CURDIR=`pwd`
  2. sk@sk:~$ echo ${CURDIR}
  3. /home/wheel/sk
  4. sk@sk:~$ cd /tmp
  5. sk@sk:/tmp$ echo ${CURDIR}
  6. /home/wheel/sk
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Re: Script to Change file permissions

 
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  #5
Jun 23rd, 2009
This is a better illustration of using ticks. It evaluates the command instead of taking the literal value:
Shell Scripting Syntax (Toggle Plain Text) 
  1. sk@sk:/tmp$ CURDIR=pwd
  2. sk@sk:/tmp$ echo ${CURDIR}
  3. pwd
  4. sk@sk:/tmp$ CURDIR=`pwd`
  5. sk@sk:/tmp$ echo ${CURDIR}
  6. /tmp
Scott Knake
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Apex Software, Inc.
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Re: Script to Change file permissions

 
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  #6
Jun 23rd, 2009
thanks...

Now I understand how it works on shell prompt.
I will try to find out if this works when written in a script.

edit: it works in scripts also...
thanks again.
Last edited by grvs; Jun 23rd, 2009 at 11:58 am.
When I was in 10th i thought I knew all the maths, when I came to graduate level, I thought there is something I didn't know about, and when I completed my PhD, i knew that I don't know anything about maths.
life's like math
oh btw... I haven't done PhD
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Re: Script to Change file permissions

 
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  #7
Jun 23rd, 2009
The prompt and script are basically identical. If it works on the prompt it works in a script

There may be a few minor differences but I can't think if any. Here is an example:

Shell Scripting Syntax (Toggle Plain Text) 
  1. sk@sk:/tmp$ if test -f /etc/passwd
  2. > then
  3. > echo "it exists"
  4. > else
  5. > echo "it doesnt exist"
  6. > fi
  7. it exists
Scott Knake
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Re: Script to Change file permissions

 
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  #8
Jun 23rd, 2009
ok.... that helps..
thanks again.
When I was in 10th i thought I knew all the maths, when I came to graduate level, I thought there is something I didn't know about, and when I completed my PhD, i knew that I don't know anything about maths.
life's like math
oh btw... I haven't done PhD
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