Книга: Fedora™ Unleashed, 2008 edition

File Operators

File Operators

The following operators can be used as file comparison operators:

? -d — To ascertain whether a file is a directory

? -f — To ascertain whether a file is a regular file

? -r — To ascertain whether read permission is set for a file

? -s — To ascertain whether a file exists and has a length greater than zero

? -w — To ascertain whether write permission is set for a file

? -x — To ascertain whether execute permission is set for a file

Assume that a shell program called compare3 is in a directory with a file called file1 and a subdirectory dir1 under the current directory. Assume that file1 has a permission of r-x (read and execute permission) and dir1 has a permission of rwx (read, write, and execute permission). The code for the shell program would look like this:

#!/bin/sh
if [ -d $dir1 ]; then
 echo "dir1 is a directory"
else
 echo "dir1 is not a directory"
fi
if [ -f $dir1 ]; then
 echo "dir1 is a regular file"
else
 echo "dir1 is not a regular file"
fi
if [ -r $file1 ]; then
 echo "file1 has read permission"
else
 echo "file1 does not have read permission"
fi
if [ -w $file1 ]; then
 echo "file1 has write permission"
else
 echo "file1 does not have write permission"
fi
if [ -x $dir1 ]; then
 echo "dir1 has execute permission"
else
 echo "dir1 does not have execute permission"
fi

If you execute the shell program, you get the following results:

dir1 is a directory
file1 is a regular file
file1 has read permission
file1 does not have write permission
dir1 has execute permission

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