Command: cat
The cat command is used to concatenate files and print them to the standard output device. It is one of the most commonly used commands in Unix-like operating systems for viewing, creating, merging, and copying files.
Usage Rights:
All users
Syntax Format:
cat [-AbeEnstTuv] [--help] [--version] fileName
Parameter Description:
-n or --number: Number all output lines starting from 1.
-b or --number-nonblank: Similar to -n but does not number blank lines.
-s or --squeeze-blank: Replace multiple consecutive blank lines with a single blank line.
-v or --show-nonprinting: Display non-printing characters using ^ and M- symbols (except for LFD and TAB).
-E or --show-ends: Display $ at the end of each line.
-T or --show-tabs: Display TAB characters as ^I.
-e: Equivalent to -vE.
-A, --show-all: Equivalent to -vET.
Examples:
Add line numbers to textfile1 and save it to textfile2:
cat -n textfile1 > textfile2
Append contents of textfile1 and textfile2 into textfile3 without adding extra blank lines:
cat -b textfile1 textfile2 >> textfile3
Empty the contents of /etc/test.txt:
cat /dev/null > /etc/test.txt
Create an image file of a floppy disk by reading from /dev/fd0:
cat /dev/fd0 > OUTFILE
Write the image file back to the floppy disk:
cat IMG_FILE > /dev/fd0
Note:
OUTFILE refers to the name of the output image file.
IMG_FILE refers to the image file you want to write back.
Ensure that the device capacity matches when writing back to the device.
Commonly used for creating boot disks.
Command: chattr
The Linux chattr command is used to change file attributes on the ext2 file system. These attributes can control various behaviors such as preventing modification, ignoring access times, and more.
Available modes include:
- Immutable: Prevents the file from being modified.
- No access time update: Does not update the last access time.
- Compressed: Compresses the file.
- No dump: Excludes the file from being dumped.
- Append only: Allows data to be added but not deleted.
- Secure deletion: Deletes the file securely.
- Sync: Ensures immediate updates.
- Not removable: Prevents accidental deletion.
Syntax Format:
chattr [-RV][-v
Parameters:
-R: Recursively process directories.
-v: Set the version number.
-V: Verbose mode.
+
-
=
Example:
Prevent a critical file from being modified:
chattr +i /etc/resolv.conf
List the attributes of a file:
lsattr /etc/resolv.conf
This will display something like:
----i-------- /etc/resolv.conf
Make a file append-only, suitable for log files:
chattr +a /var/log/messages
Command: chgrp
The chgrp command is used to change the group ownership of a file or directory in a UNIX-like system. This allows for better management of file access permissions based on group settings.
Usage Rights:
Root user
Syntax Format:
chgrp [-cfhRv][--help][--version][group][file or directory...] or chgrp [-cfhRv][--help][--reference=
Parameters:
-c or --changes: Only show changes made.
-f or --quiet: Suppress error messages.
-h or --no-dereference: Do not follow symbolic links.
-R or --recursive: Process directories recursively.
-v or --verbose: Show detailed information.
--reference: Set the group to match that of another file or directory.
Example:
Change the group of a file to 'bin':
chgrp -v bin log2012.log
Change the group of a file to match another file's group:
chgrp --reference=log2012.log log2013.log
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