Command: cat
The cat command is used to concatenate and display the contents of files. It can also be used to create new files or append content to existing ones.
Use 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: Number non-blank lines only.
-s or --squeeze-blank: Replace multiple blank lines with a single one.
-v or --show-nonprinting: Display non-printing characters using ^ and M- notation, except for LFD and TAB.
-E or --show-ends: Show $ 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.
Instance
Add line numbers to textfile1 and save it in textfile2:
Cat -n textfile1 > textfile2
Append the contents of textfile1 and textfile2 to textfile3, without numbering blank lines:
Cat -b textfile1 textfile2 >> textfile3
Empty the contents of /etc/test.txt:
Cat /dev/null > /etc/test.txt
Cat can also be used to create disk images. For example, to create an image of a floppy disk:
Cat /dev/fd0 > OUTFILE
To write the image back to the floppy disk:
Cat IMG_FILE > /dev/fd0
Note: Ensure the device capacity matches when writing back from an image file. This is commonly used for creating boot disks.
Command: chattr
The Linux chattr command is used to change file attributes on ext2 file systems.
These attributes include: immutable, no access time update, compressed, not dumped, not changed, secure deletion, synchronous updates, and not deletable.
Syntax Format
Chattr [-RV][-v
Parameter Description
-R: Recursively process directories.
-v
-V: Display detailed information.
+
-
=
Instance
Prevent a critical file from being modified:
Chattr +i /etc/resolv.conf
Let a file only allow appending data:
Chattr +a /var/log/messages
Command: chgrp
The Linux chgrp command changes the group ownership of a file or directory.
Syntax Format
Chgrp [-cfhRv][--help][--version][group][file or directory...] or chgrp [-cfhRv][--help][--reference=
Parameter Description
-c or --changes: Show only changes made.
-f or --quiet: Suppress error messages.
-h or --no-dereference: Modify symbolic links only.
-R or --recursive: Process recursively.
-v or --verbose: Display detailed information.
--reference: Set the group based on another file.
Instance
Change the group of a file:
Chgrp -v bin log2012.log
Change the group based on a reference file:
Chgrp --reference=log2012.log log2013.log
Command: chmod
Linux/Unix file permissions are divided into owner, group, and others. Use chmod to control access to files.
Use Rights
All users
Syntax Format
Chmod [-cfvR] [--help] [--version] mode file...
Parameter Description
Mode: Permission setting string with format [ugoa...][[+-=][rwxX]...][,...].
Other parameters like -c, -f, -v, -R, etc., are available for detailed control.
Instance
Make a file readable by everyone:
Chmod ugo+r file1.txt
Set specific permissions using numeric values:
Chmod 777 file
This sets read, write, and execute permissions for all users.
Command: chown
The Linux chown command changes the owner of a file or directory.
Only root has permission to change ownership of other users' files.
Syntax Format
Chown [-cfhvR] [--help] [--version] user[:group] file...
Parameter Description
User: New owner of the file.
Group: New group of the file.
Instance
Change the owner of a file:
Chown jessie:users file1.txt
Change ownership recursively:
Chown -R lamport:users *
Command: cksum
The cksum command checks the CRC of a file to ensure its integrity during transfers.
It uses a checksum algorithm to detect errors.
Syntax Format
Cksum [--help][--version][file...]
Parameter Description
--help: Online help.
--version: Display version information.
Instance
Check the integrity of a file:
$ cksum testfile1
Output: 1263453430 78 testfile1
If the file is modified, the checksum will change.
Command: cmp
The cmp command compares two files for differences.
If the files are identical, no output is displayed. Otherwise, it shows the first differing character and position.
Syntax Format
Cmp [-clsv][-i
Parameter Description
-c: Display characters along with their decimal codes.
-i: Ignore initial characters.
-l: Display all differences.
Instance
Compare two files:
Cmp prog.o.bak prog.o
If they differ, the output might be: prog.o.bak prog.o differ: char 4, line 1.
Command: diff
The diff command compares text files line by line.
It can also compare directories, but not subdirectories.
Syntax Format
Diff [-abBcdefHilnNpPqrstTuvwy][-
Parameter Description
-c: Display all text and mark differences.
-y: Side-by-side comparison.
Instance
Compare two files:
[root@localhost test3]# diff log2014.log log2013.log
Output includes differences in lines and added/deleted content.
Command: diffstat
The diffstat command displays statistics from diff outputs, showing insertions, deletions, and modifications per file.
Syntax Format
Diff [-wV][-n
Instance
Use diff and pipe to diffstat for statistical results:
$ diff test1 test2 | diffstat
This helps in quickly understanding the changes between files.
Command: file
The file command identifies the type of a file.
Syntax Format
File [-bcLvz][-f
Parameter Description
-b: Do not display the file name.
-c: Display detailed execution steps.
-L: Display the category of the file pointed to by a symbolic link.
Instance
Identify a file's type:
[root@localhost ~]# file install.log
Install.log: UTF-8 Unicode text
[root@localhost ~]# file -i install.log
Install.log: text/plain; charset=utf-8
Command: find
The find command searches for files in specified directories.
Syntax Format
Find path -option [ -print ] [ -exec -ok command ] {} ;
Parameter Description
Options like -name, -type, -mtime, and -perm are used for filtering.
Instance
List all .c files in the current directory and subdirectories:
# find . -name "*.c"
Find all files modified within the last 20 days:
# find . -ctime -20
Delete files older than 7 days:
$ find /var/logs -type f -mtime +7 -ok rm { } ;
Command: git
The git command is a text-based file manager with an interactive interface.
It allows users to navigate, edit, and manage files easily.
Instructions
F1: View help information.
F2: List file contents.
F3: View file contents.
F4: Edit file contents.
F5: Copy files or directories.
F6: Move or rename files or directories.
F7: Create a directory.
F8: Delete files or directories.
F9: Execute make commands.
F10: Exit the git file manager.
Command: gitview
The gitview command displays file contents in both hexadecimal and ASCII formats.
Syntax Format
Gitview [-bchilv][file]
Parameter Description
-c: Display in color mode.
-h: Show help instructions.
Instance
View the contents of a file in color mode:
$ gitview -c /home/rootlocal/demo.txt
Command: indent
The indent command adjusts the formatting of C source code files.
It helps in making code more readable by applying consistent indentation and spacing rules.
Syntax Format
Indent [parameter][source file] or indent [parameter][source file][-o target file]
Parameter Description
Various options control indentation, braces placement, comment formatting, etc.
Instance
Format a C source file with default settings:
$ indent -linux program.c
Adjust indentation level to 4 spaces:
$ indent -i4 program.c
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