The grep utility is used to parse through existing files in search of matching strings. With its options, it can return output in a variety of ways.
Example: Finding all uses of a word To find all uses of the word "Passing" (in any case) in the file scores.txt, and write with line numbers in the commands output:
# /usr/bin/grep -i -n Passing scores.txt
Example: Finding all empty lines To find all empty lines in the standard input:
# /usr/bin/grep ^$ or # /usr/bin/grep -v .
Example: Finding lines containing strings Both of the following commands print all lines containing
strings abc or def or both:
# grep -E 'abc def'
# grep -F 'abc def'
2. List in sequence the steps to create, modify, and delete access control lists (ACLs)on files.
Access control lists provide a mechanism for finer control over the basic UNIX file permissions. They offer extended protection over and above what is provided by standard UNIX file permissions. A file has an acl set if its output in the ls has a '+' at the end of the permissions mode field.
The setfacl command is used to set a file ACL.
setfacl options acl_entry filename1 [ filename2 filename3 ... ]
For example, to give read access to another user on a file you own:
setfacl -m user:reader1:6 newtext.txt
would assign read only access to the user reader1
To verify that ACLs were set for the file, run
# getfacl
# file: newtext.txt
# owner: reader1
# group: users
user::rw-
user:reader1:r-- #effective:r--
group::r-- #effective:r--
mask:r--
other:r--
To remove an ACL from the file, run:
setfacl -d user:reader1:6 newtext.txt
