There are three specific permissions on Unix-like (including Linux / Mac OS x) systems that apply to each user or class:
=> The read permission (r), which grants the ability to read a file. When set for a directory, this permission grants the ability to read the names of files in the directory
=> The write permission (w), which grants the ability to modify a file. When set for a directory, this permission grants the ability to modify entries in the directory. This includes creating files, deleting files, and renaming files.
=> The execute permission (x), which grants the ability to execute a file. This permission must be set for executable binaries in order to allow the operating system to run them. When set for a directory, this permission grants the ability to traverse its tree in order to access files or subdirectories, but not see files inside the directory (unless read is set).
SHELL CONDITIONAL EXPRESSIONS
You can use conditional expressions to find out file permissions. These are used by the [[ compound command and the test and [ builtin commands to test file attributes and perform string and arithmetic comparisons.
| Conditional Expression | Meaning |
| -a file | True if file exists. |
| -b file | True if file exists and is a block special file. |
| -c file | True if file exists and is a character special file. |
| -d file | True if file exists and is a directory. |
| -e file | True if file exists. |
| -f file | True if file exists and is a regular file. |
| -g file | True if file exists and is set-group-id. |
| -h file | True if file exists and is a symbolic link. |
| -k file | True if file exists and its “sticky” bit is set. |
| -p file | True if file exists and is a named pipe (FIFO). |
| -r file | True if file exists and is readable. |
| -s file | True if file exists and has a size greater than zero. |
| -t fd | True if file descriptor fd is open and refers to a terminal. |
| -u file | True if file exists and its set-user-id bit is set. |
| -w file | True if file exists and is writable. |
| -x file | True if file exists and is executable. |
| -O file | True if file exists and is owned by the effective user id. |
| -G file | True if file exists and is owned by the effective group id. |
| -L file | True if file exists and is a symbolic link. |
| -S file | True if file exists and is a socket. |
| -N file | True if file exists and has been modified since it was last read. |
Sample Shell Script
#!/bin/bash # Shell script to find out whether file has read, write and execute # permission # ------------------------------------------------------------------------- # Copyright (c) 2005 nixCraft project <http://cyberciti.biz/fb/> # This script is licensed under GNU GPL version 2.0 or above # ------------------------------------------------------------------------- # This script is part of nixCraft shell script collection (NSSC) # Visit http://bash.cyberciti.biz/ for more information. # ------------------------------------------------------------------------- echo -n "Enter file name : " read file # find out if file has write permission or not [ -w $file ] && W="Write = yes" || W="Write = No" # find out if file has excute permission or not [ -x $file ] && X="Execute = yes" || X="Execute = No" # find out if file has read permission or not [ -r $file ] && R="Read = yes" || R="Read = No" echo "$file permissions" echo "$W" echo "$R" echo "$X"
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How to write a shell script to display the specified number of lines from the given file. Accept a file name and check whether the file name entered exists and has both read and write permission for the owner and the number of lines should be > 0 and < 20. ???
echo "Executable files in the current directory...." for File in * do if [ -x $File ] then echo $File fi done echo "Directories in the current directory...." for dir in * do if [ -d $dir ] then echo $dir fi done echo "Zero sized files in the current directory...." for file in `find -type f -size 0c` do echo $file done// Coded by the Remo echo -n "Enter the file or directory name :" read name if test -f $name then echo "Its is a file and it has " if test -r $name then echo "Read permission " fi if test -w $name then echo "Write permission " fi if test -x $name then echo "Execute permission " fi elif test -d $name then echo "Its is a directory and it has " if test -r $name then echo "Read permission " fi if test -w $name then echo "Write permission " fi if test -x $name then echo "Execute permission " fi else echo "Does not find any file or directory named $name fi// Coded by the Remo echo -n "Enter the file or directory name :" read name if test -f $name then echo "Its is a file and it has " if test -r $name then echo "Read permission " fi if test -w $name then echo "Write permission " fi if test -x $name then echo "Execute permission " fi elif test -d $name then echo "Its is a directory and it has " if test -r $name then echo "Read permission " fi if test -w $name then echo "Write permission " fi if test -x $name then echo "Execute permission " fi else echo "Does not find any file or directory named $name fihow to know the files and file permissions from directory
How can I compare permission of two different files?
I need code which will give me permission for group or other on given file. does anybody has it ???
#in my current dir files are imagin
# there are 3 files …dhiraj (dhiraj _ r w x r w x r w x),yasin(_ r _ _ _ _ _ _ _),
#shell1(_r _ _ r_ x _ _ _)
#it use for all person like group,other and user
for $filename in `ls`
do
if [ -w $filename -a -r $filename -a -x $filename ]
then
echo $filename
fi
done
#output
dhiraj
echo enter the filename read file gr=` ls -li $file | cut -c13` gw=` ls -li $file | cut -c14` gx=` ls -li $file | cut -c15` if test $gr = r then echo $file has read permissoin fi if test $gw = w then echo $file has write permissoin fi if test $gx = x then echo $file has execute permissoin ficlear
echo “Enter the filename:”
read f1
if [ -f $f1 ]
then
if [ -r $f1 ]
then
if [ -w $f1 ]
echo “File is reable and writable”
else
echo “reable”
fi
else
echo “writable”
fi
else
echo “the entered name is not a file”
fi
~
~
~
Good work