Master Linux Command Line: cat, chattr, chgrp, chmod, find and More Explained

cat

The cat command concatenates files and prints their contents to standard output.

Usage

All users can run the command.

Syntax

cat [-AbeEnstTuv] [--help] [--version] fileName

Options

-n

or --number: number all output lines starting at 1. -b or --number-nonblank: number non‑blank lines only. -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‑ notation, except LFD and TAB. -E or --show-ends: display $ at line ends. -T or --show-tabs: display TAB characters as ^I. -e: equivalent to -vE. -A, --show-all: equivalent to -vET.

Examples

cat -n textfile1 > textfile2

cat -b textfile1 textfile2 >> textfile3

cat /dev/null > /etc/test.txt

cat /dev/fd0 > OUTFILE   # create floppy image

cat IMG_FILE > /dev/fd0   # write image to floppy

chattr

The chattr command changes file attributes on ext2/3/4 file systems.

Syntax

chattr [-RV][-v<version>][+/-=<attr>] file...

Options

-R

: recursively process directories. -v<version>: set file version. -V: verbose output. +<attr>: add attribute. -<attr>: remove attribute. =<attr>: set exact attribute.

Examples

chattr +i /etc/resolv.conf   # make immutable

lsattr /etc/resolv.conf

chattr +a /var/log/messages   # append‑only

chgrp

The chgrp command changes the group ownership of files or directories.

Syntax

chgrp [-cfhRv][--help][--version] group file...

chgrp [-cfhRv][--help][--reference=<ref>][--version] file...

Options

-c

or --changes: report only when a change is made. -f or --quiet or --silent: suppress error messages. -h or --no-dereference: affect symbolic links themselves. -R or --recursive: recurse into directories. -v or --verbose: verbose output. --help: display help. --reference=<ref>: set group to match that of the reference file. --version: display version.

Examples

chgrp -v bin log2012.log

chgrp --reference=log2012.log log2013.log

chmod

The chmod command modifies file permission bits.

Syntax

chmod [-cfvR] [--help] [--version] mode file...

Mode format

[ugoa...][[+-=][rwxX]...][,...]

Options

-c

: report only when a change is made. -f: suppress error messages. -v: verbose output. -R: apply recursively. --help: display help. --version: display version.

Examples

chmod ugo+r file1.txt

chmod a+r file1.txt

chmod ug+w,o-w file1.txt file2.txt

chmod u+x ex1.py

chmod -R a+r *

chmod 777 file

chmod abc file   # a,b,c represent user, group, other permissions

chown

The chown command changes file owner and/or group.

Syntax

chown [-cfhvR] [--help] [--version] user[:group] file...

Options

-c

: report only when a change is made. -f: suppress errors. -h: affect symbolic links themselves. -v: verbose output. -R: recursive. --help: help. --version: version.

Examples

chown jessie:users file1.txt

chown -R lamport:users *

cksum

The cksum command computes a CRC checksum and byte count for files.

Syntax

cksum [--help][--version][file...]

Options

--help

: display help. --version: display version.

Example

cksum testfile1

Output shows checksum, byte count, and filename.

cmp

The cmp command compares two files byte by byte.

Syntax

cmp [-clsv][-i <bytes>][--help] file1 file2

Options

-c

or --print-chars: show differing characters. -i<bytes> or --ignore-initial=<bytes>: skip initial bytes. -l or --verbose: list all differences. -s or --quiet: silent mode. -v or --version: version. --help: help.

Example

cmp prog.o.bak prog.o

If files differ, the first differing byte and line are reported.

diff

The diff command compares files line by line.

Syntax

diff [options] file1 file2

Common options

-a

or --text: treat all files as text. -b or --ignore-space-change: ignore changes in whitespace. -B or --ignore-blank-lines: ignore blank lines. -c: context diff. -u or --unified: unified diff. -r or --recursive: recurse into directories. -q or --brief: report only if files differ. --help: help.

Examples

diff log2014.log log2013.log

diff -y -W 50 log2014.log log2013.log

Symbols |, <, and > indicate differences, missing lines, and extra lines respectively.

diffstat

The diffstat command summarizes the output of diff, showing insertions and deletions per file.

Syntax

diffstat [-wV] [-n <len>] [-p <len>] [-w <width>]

Example

diff -r test1 test2 | diffstat

Displays a concise change summary.

file

The file command determines the type of a file.

Syntax

file [-bcLvz] [-f namefile] [-m magicfile...] file...

Options

-b

: omit filename in output. -c: verbose (debug) output. -L: follow symbolic links. -v: version. -z: try to examine compressed files.

Example

file install.log

Output:

install.log: UTF-8 Unicode text

find

The find command searches for files and directories matching given criteria.

Syntax

find path [expression]

Common options

-name

pattern : match filename. -iname pattern : case‑insensitive name match. -type c : file type (f, d, l, etc.). -size n : file size. -perm mode : match permission bits. -mtime n : modification time. -exec command {} \\; : execute command on each match. -ok command {} \\; : like -exec but ask before execution.

Examples

find . -name "*.c"

find . -type f

find . -ctime -20

find /var/logs -type f -mtime +7 -ok rm {} \;

find . -type f -perm 644 -exec ls -l {} \;

find / -type f -size 0 -exec ls -l {} \;

git

The git command in this context refers to a text‑mode file manager offering shortcuts for common operations.

Key shortcuts

F1 – info

F2 – cat (display file)

F3 – gitview (hex/ASCII view)

F4 – vi (edit)

F5 – cp (copy)

F6 – mv (move/rename)

F7 – mkdir (create directory)

F8 – rm (delete)

F9 – make (run build commands)

F10 – exit

gitview

The gitview command displays a file in both hexadecimal and ASCII formats.

Syntax

gitview [-bchilv] file

Options

-b

: monochrome mode. -c: color mode. -h: help. -i: show program location. -l: no previous screen. -v: version.

Example

gitview -c /home/rootlocal/demo.txt

indent

The indent command reformats C source code according to specified style options.

Syntax

indent [options] source.c [-o output.c]

Selected options

-bad

or --blank-lines-after-declarations: add blank line after declarations. -bap or --blank-lines-after-procedures: add blank line after functions. -bl or --braces-after-if-line: place { on a new line after if. -i<n> or --indent-level<n>: set indentation width. -kr or --k-and-r-style: use Kernighan & Ritchie style. -gnu or --gnu-style: use GNU style (default). -ut or --use-tabs: indent with tabs. -ts<n> or --tab-size<n>: set tab size.

Example

indent -gnu -i4 -ut source.c -o formatted.c