ls command examples, Introduction to ls command in Linux, How to: Use ls in Linux

ls is a command used to list files and folders within a directory or folder

1 ls command

ls
ls
ls

2 Use long listing format

ls -l

-l: Long listing format

ls with long listing format
ls with long listing format

Column 1: drwxr-xr-x:

The first d means it’s directory if it’s – rather than d means it’s file, if it’s not d or – but l means it’s symbolic link.

Following 9 characters represents the file permission. First 3 rwx represents the file owner’s permission, Second 3 rwx represents the group’s file permission, Third 3 rwx represents others’ file permission

Column 2: 26: How many symbolic link points to this file

Column 3: abc: File/Directory owner

Column 4: abc: File/Directory group

Column 5: 4096: File/Directory size in bytes. For directories, it will always show 4096 bytes

Column 6: Mar 2 22:50: Last time the file was modified

Column 7: annaconda3: File/Directory name

For more information on permission/ Privilege, refer to: Unix/Linux (Ubuntu, Debian, Kali Linux etc.) Privilege Management

3 Show file size

ls -hl
 
or
 
ls -lsi

-h: human readable units (1024)

-si: human readable units (1000)

ls - hl
ls – hl
ls -lsi
ls -lsi

4 Sort the results by size

ls -hlS

-S: sort by file size, largest first

ls -hlS
ls -hlS

5 Specify units

ls -l --block-size=G
K = Kilobyte
M = Megabyte
G = Gigabyte
T = Terabyte
P = Petabyte
E = Exabyte
Z = Zettabyte
Y = Yottabyte
ls -l --block-size=G
ls -l –block-size=G

6 Show hidden files

In Linux, files begin with “.” are hidden. we can use -a switch with ls to show them

ls -a
ls -a
ls -a

7 Only list directories

ls -d */
Only list directories
Only list directories

8 Do not list owner

ls -g
Do not list owner
Do not list owner

9 Do not list group names in a long listing

ls -lG
Do not list group names in a long listing
Do not list group names in a long listing

10 Show UID and GID

ls -n
Show UID and GID
Show UID and GID

11 Print without colour

ls --color=never
Print without colour
Print without colour

12 Show index number of each file (inode)

ls -li
Show index number of each file (inode)
Show index number of each file (inode)

13 Append / indicator to directories

ls -p
Append / indicator to directories
Append / indicator to directories

14 Reverse sorting results

ls -r
Reverse sorting results
Reverse sorting results

15 List subdirectories recursively

ls -R
List subdirectories recursively
List subdirectories recursively

16 Sort alphabetically by entry extension

ls -lX
Sort alphabetically by entry extension method 1
Sort alphabetically by entry extension method 1

OR

ls -sort=extension
Sort alphabetically by entry extension method 2
Sort alphabetically by entry extension method 2

17 Sort by modification time (Latest at the top)

ls -lt
Sort by modification time (Latest at the top)
Sort by modification time (Latest at the top)

18 List folders/files for home directory

ls ~
List folders/files for home directory
List folders/files for home directory

19 List folders/files for parent directory

ls ../
List folders/files for parent directory
List folders/files for parent directory

List directory/files for parent of parent directory

ls ../../
List directory/files for parent of parent directory
List directory/files for parent of parent directory

20 Show ls version information

ls -version
Show ls version information
Show ls version information

Help page of ls

Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
Mandatory arguments to long options are mandatory for short options too.
  -a, --all                  do not ignore entries starting with .
  -A, --almost-all           do not list implied . and ..
      --author               with -l, print the author of each file
  -b, --escape               print C-style escapes for nongraphic characters
      --block-size=SIZE      with -l, scale sizes by SIZE when printing them;
                               e.g., '--block-size=M'; see SIZE format below
  -B, --ignore-backups       do not list implied entries ending with ~
  -c                         with -lt: sort by, and show, ctime (time of last
                               modification of file status information);
                               with -l: show ctime and sort by name;
                               otherwise: sort by ctime, newest first
  -C                         list entries by columns
      --color[=WHEN]         colorize the output; WHEN can be 'always' (default
                               if omitted), 'auto', or 'never'; more info below
  -d, --directory            list directories themselves, not their contents
  -D, --dired                generate output designed for Emacs' dired mode
  -f                         do not sort, enable -aU, disable -ls --color
  -F, --classify             append indicator (one of */=>@|) to entries
      --file-type            likewise, except do not append '*'
      --format=WORD          across -x, commas -m, horizontal -x, long -l,
                               single-column -1, verbose -l, vertical -C
      --full-time            like -l --time-style=full-iso
  -g                         like -l, but do not list owner
      --group-directories-first
                             group directories before files;
                               can be augmented with a --sort option, but any
                               use of --sort=none (-U) disables grouping
  -G, --no-group             in a long listing, don't print group names
  -h, --human-readable       with -l and -s, print sizes like 1K 234M 2G etc.
      --si                   likewise, but use powers of 1000 not 1024
  -H, --dereference-command-line
                             follow symbolic links listed on the command line
      --dereference-command-line-symlink-to-dir
                             follow each command line symbolic link
                               that points to a directory
      --hide=PATTERN         do not list implied entries matching shell PATTERN
                               (overridden by -a or -A)
      --hyperlink[=WHEN]     hyperlink file names; WHEN can be 'always'
                               (default if omitted), 'auto', or 'never'
      --indicator-style=WORD  append indicator with style WORD to entry names:
                               none (default), slash (-p),
                               file-type (--file-type), classify (-F)
  -i, --inode                print the index number of each file
  -I, --ignore=PATTERN       do not list implied entries matching shell PATTERN
  -k, --kibibytes            default to 1024-byte blocks for disk usage;
                               used only with -s and per directory totals
  -l                         use a long listing format
  -L, --dereference          when showing file information for a symbolic
                               link, show information for the file the link
                               references rather than for the link itself
  -m                         fill width with a comma separated list of entries
  -n, --numeric-uid-gid      like -l, but list numeric user and group IDs
  -N, --literal              print entry names without quoting
  -o                         like -l, but do not list group information
  -p, --indicator-style=slash
                             append / indicator to directories
  -q, --hide-control-chars   print ? instead of nongraphic characters
      --show-control-chars   show nongraphic characters as-is (the default,
                               unless program is 'ls' and output is a terminal)
  -Q, --quote-name           enclose entry names in double quotes
      --quoting-style=WORD   use quoting style WORD for entry names:
                               literal, locale, shell, shell-always,
                               shell-escape, shell-escape-always, c, escape
                               (overrides QUOTING_STYLE environment variable)
  -r, --reverse              reverse order while sorting
  -R, --recursive            list subdirectories recursively
  -s, --size                 print the allocated size of each file, in blocks
  -S                         sort by file size, largest first
      --sort=WORD            sort by WORD instead of name: none (-U), size (-S),
                               time (-t), version (-v), extension (-X)
      --time=WORD            with -l, show time as WORD instead of default
                               modification time: atime or access or use (-u);
                               ctime or status (-c); also use specified time
                               as sort key if --sort=time (newest first)
      --time-style=TIME_STYLE  time/date format with -l; see TIME_STYLE below
  -t                         sort by modification time, newest first
  -T, --tabsize=COLS         assume tab stops at each COLS instead of 8
  -u                         with -lt: sort by, and show, access time;
                               with -l: show access time and sort by name;
                               otherwise: sort by access time, newest first
  -U                         do not sort; list entries in directory order
  -v                         natural sort of (version) numbers within text
  -w, --width=COLS           set output width to COLS.  0 means no limit
  -x                         list entries by lines instead of by columns
  -X                         sort alphabetically by entry extension
  -Z, --context              print any security context of each file
  -1                         list one file per line.  Avoid '\n' with -q or -b
      --help     display this help and exit
      --version  output version information and exit
The SIZE argument is an integer and optional unit (example: 10K is 10*1024).
Units are K,M,G,T,P,E,Z,Y (powers of 1024) or KB,MB,... (powers of 1000).
The TIME_STYLE argument can be full-iso, long-iso, iso, locale, or +FORMAT.
FORMAT is interpreted like in date(1).  If FORMAT is FORMAT1<newline>FORMAT2,
then FORMAT1 applies to non-recent files and FORMAT2 to recent files.
TIME_STYLE prefixed with 'posix-' takes effect only outside the POSIX locale.
Also the TIME_STYLE environment variable sets the default style to use.
Using color to distinguish file types is disabled both by default and
with --color=never.  With --color=auto, ls emits color codes only when
standard output is connected to a terminal.  The LS_COLORS environment
variable can change the settings.  Use the dircolors command to set it.
Exit status:
 0  if OK,
 1  if minor problems (e.g., cannot access subdirectory),
 2  if serious trouble (e.g., cannot access command-line argument).
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation at: <https://www.gnu.org/software/coreutils/ls>
or available locally via: info '(coreutils) ls invocation'

Man page of ls

LS(1)                                    User Commands                                   LS(1)
NAME
       ls - list directory contents
SYNOPSIS
       ls [OPTION]... [FILE]...
DESCRIPTION
       List  information about the FILEs (the current directory by default).  Sort entries al‐
       phabetically if none of -cftuvSUX nor --sort is specified.
       Mandatory arguments to long options are mandatory for short options too.
       -a, --all
              do not ignore entries starting with .
       -A, --almost-all
              do not list implied . and ..
       --author
              with -l, print the author of each file
       -b, --escape
              print C-style escapes for nongraphic characters
       --block-size=SIZE
              with -l, scale sizes by SIZE when printing  them;  e.g.,  '--block-size=M';  see
              SIZE format below
       -B, --ignore-backups
              do not list implied entries ending with ~
       -c     with -lt: sort by, and show, ctime (time of last modification of file status in‐
              formation); with -l: show ctime and sort by name; otherwise: sort by ctime, new‐
              est first
       -C     list entries by columns
       --color[=WHEN]
              colorize  the  output;  WHEN  can  be  'always' (default if omitted), 'auto', or
              'never'; more info below
       -d, --directory
              list directories themselves, not their contents
       -D, --dired
              generate output designed for Emacs' dired mode
       -f     do not sort, enable -aU, disable -ls --color
       -F, --classify
              append indicator (one of */=>@|) to entries
       --file-type
              likewise, except do not append '*'
       --format=WORD
              across -x, commas -m, horizontal -x, long -l, single-column -1, verbose -l, ver‐
              tical -C
       --full-time
              like -l --time-style=full-iso
       -g     like -l, but do not list owner
       --group-directories-first
              group directories before files;
              can  be augmented with a --sort option, but any use of --sort=none (-U) disables
              grouping
       -G, --no-group
              in a long listing, don't print group names
       -h, --human-readable
              with -l and -s, print sizes like 1K 234M 2G etc.
       --si   likewise, but use powers of 1000 not 1024
       -H, --dereference-command-line
              follow symbolic links listed on the command line
       --dereference-command-line-symlink-to-dir
              follow each command line symbolic link
              that points to a directory
       --hide=PATTERN
              do not list implied entries matching shell PATTERN (overridden by -a or -A)
       --hyperlink[=WHEN]
              hyperlink file names; WHEN can be 'always'  (default  if  omitted),  'auto',  or
              'never'
       --indicator-style=WORD
              append  indicator  with  style  WORD to entry names: none (default), slash (-p),
              file-type (--file-type), classify (-F)
       -i, --inode
              print the index number of each file
       -I, --ignore=PATTERN
              do not list implied entries matching shell PATTERN
       -k, --kibibytes
              default to 1024-byte blocks for disk usage; used only with -s and per  directory
              totals
       -l     use a long listing format
       -L, --dereference
              when showing file information for a symbolic link, show information for the file
              the link references rather than for the link itself
       -m     fill width with a comma separated list of entries
       -n, --numeric-uid-gid
              like -l, but list numeric user and group IDs
       -N, --literal
              print entry names without quoting
       -o     like -l, but do not list group information
       -p, --indicator-style=slash
              append / indicator to directories
       -q, --hide-control-chars
              print ? instead of nongraphic characters
       --show-control-chars
              show nongraphic characters as-is (the default, unless program is 'ls' and output
              is a terminal)
       -Q, --quote-name
              enclose entry names in double quotes
       --quoting-style=WORD
              use  quoting  style  WORD for entry names: literal, locale, shell, shell-always,
              shell-escape, shell-escape-always, c, escape (overrides  QUOTING_STYLE  environ‐
              ment variable)
       -r, --reverse
              reverse order while sorting
       -R, --recursive
              list subdirectories recursively
       -s, --size
              print the allocated size of each file, in blocks
       -S     sort by file size, largest first
       --sort=WORD
              sort by WORD instead of name: none (-U), size (-S), time (-t), version (-v), ex‐
              tension (-X)
       --time=WORD
              with -l, show time as WORD instead of default modification time: atime or access
              or  use  (-u);  ctime  or  status  (-c);  also use specified time as sort key if
              --sort=time (newest first)
       --time-style=TIME_STYLE
              time/date format with -l; see TIME_STYLE below
       -t     sort by modification time, newest first
       -T, --tabsize=COLS
              assume tab stops at each COLS instead of 8
       -u     with -lt: sort by, and show, access time; with -l: show access time and sort  by
              name; otherwise: sort by access time, newest first
       -U     do not sort; list entries in directory order
       -v     natural sort of (version) numbers within text
       -w, --width=COLS
              set output width to COLS.  0 means no limit
       -x     list entries by lines instead of by columns
       -X     sort alphabetically by entry extension
       -Z, --context
              print any security context of each file
       -1     list one file per line.  Avoid '\n' with -q or -b
       --help display this help and exit
       --version
              output version information and exit
       The SIZE argument is an integer and optional unit (example: 10K is 10*1024).  Units are
       K,M,G,T,P,E,Z,Y (powers of 1024) or KB,MB,... (powers of 1000).
       The TIME_STYLE argument can be full-iso, long-iso, iso, locale, or +FORMAT.  FORMAT  is
       interpreted  like  in  date(1).  If FORMAT is FORMAT1<newline>FORMAT2, then FORMAT1 ap‐
       plies to non-recent files and  FORMAT2  to  recent  files.   TIME_STYLE  prefixed  with
       'posix-'  takes  effect only outside the POSIX locale.  Also the TIME_STYLE environment
       variable sets the default style to use.
       Using  color  to  distinguish  file  types  is  disabled  both  by  default  and   with
       --color=never.   With  --color=auto,  ls emits color codes only when standard output is
       connected to a terminal.  The LS_COLORS environment variable can change  the  settings.
       Use the dircolors command to set it.
   Exit status:
       0      if OK,
       1      if minor problems (e.g., cannot access subdirectory),
       2      if serious trouble (e.g., cannot access command-line argument).
AUTHOR
       Written by Richard M. Stallman and David MacKenzie.
REPORTING BUGS
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report ls translation bugs to <https://translationproject.org/team/>
COPYRIGHT
       Copyright  ©  2018 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or
       later <https://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There  is  NO  WAR‐
       RANTY, to the extent permitted by law.
SEE ALSO
       Full documentation at: <https://www.gnu.org/software/coreutils/ls>
       or available locally via: info '(coreutils) ls invocation'
GNU coreutils 8.30                        August 2019                                    LS(1)

Simple usage of xargs, tr, head, tail commands

1 xargs

Similar to -exec

Delete .txt files from current folder

find . -name "*.txt" | xargs rm

Count line numbers in all .txt files

find . -name "*.txt" | xargs wc -l

2 tr

Replace

Replace capital with small case

echo "THIS IS A TEST" | tr "A-Z" "a-z"
 
#Result this is a test

ROT13 Encrypt

echo "Test" | tr "a-zA-Z" "n-za-mN-ZA-m"
 
# Result: Grfg

ROT13 Decrypt

echo "Grfg" | tr "a-zA-Z" "n-za-mN-ZA-m"
 
# Result: Test

Remove digits from the string

echo "This 3 is 1831 a tes2t" | tr -d "0-9"
 
# Result: This  is  a test

Remove redundant space

echo "This is  a       test message     " | tr -s ' '
 
# Result: This is a test message

Remove redundant empty lines form text file

cat text.txt | tr -s '\n'

3 head

Print first 10 lines

head my.log -n 10

4 tail

Print last 10 lines

tail my.log -n 10

Different ways to search in Linux/Debian/Ubuntu/Kali Linux/CentOS/RHEL etc.

locate – Locate files

It can find files quickly but it depends on updatedb to update the index, updatedb runs once everyday but we can run it manually.

# Update the index manually if necessary
sudo updatedb
 
# Find/Search for "myfile"
locate myfile

whereis, which – Locate command/executable files

whereis ProgramName
 
which ProgramName

whereis: Will search for executable, source code and documents from default installation folder (Usually, it’s the default folder when installing with root)

Default folders are:

/bin
/sbin
/usr/bin
/usr/lib
/usr/local/ma
etc.

which: Will show results from environment variables, it’s very useful for finding where the actual program/executable located

e.g. Copy source code to current directory without typing complete path

cp 'which myScript.sh'

If which ProgramName returns /usr/bin/which: no ProgramName in (/home/usr/bin:/bin), it means the ProgramName is not located in environment variables, it can’t be executed directly by it’s name

find – Find files with multiple conditions

Search by folder

# Find files with name "myFile" under root directory
find / -name myFile

If executing the above command with non-root user, it will return many errors (Permission denied), we can use following command to ignore all errors but keep normal output

find / -name 2>/dev/null

What is 2>/dev/null ?: Refer to “I/O redirection in Linux” section in Linux – Basics, Useful Terminal commands and Basic File manipulation, (QuickStart)

Search by time

Show log files which were modified within 5 minutes in current working directory

find . -name '*.log' -mmin -5

(To show log files which were modified within 1 day in current working directory)

find . -name '*.log' -mtime -1

Search by Size

e.g. Search all jpg and bmp files

find . \( -name "*.jpg" -o -name "*.bmp" ) | less
 
or
 
find . -regex ".*\(\.jpg\|\.bmp\)$"
 
# Find files over 10G
find . -type f -size +100G

Limit search folder depth

Search for any .txt files within maximum 3 folder depth

find . -maxdepth 3 -name *.txt

Search for files which are not…

Search for files which are not .txt files

find . -not -name *.txt

find, grep Search for file contents

To list name of all .txt files with Mytext in the content

find . -name *.txt -exec grep -l 'Mytext' {} \;
 
or
 
find . -name *.txt | xargs grep -l 'Mytext'
 
or
 
grep -rl 'Mytext'

To view matched previous 2 lines and next 3 lines

grep -A 3 -B 2 'Mytext' a.txt

To view match counts

# Exact match
grep -c 'Mytext' a.txt
 
# Ignore case
grcp -ci 'Mytext' a.txt

Count number of series in FASTA and FASTQ

grep '^>' test.fa
 
grep '^+$' test.fq

^: Start with …

$: End with …

Match/Show unmatched lines

grep -v 'Mytext' a.txt

Regular Expression

By default, grep uses basic regular expression, add -E switch to use extended regular expression, add -P switch to use perl format regular expression

e.g. Remove all blank lines from text file

grep -v '^$' a.txt >a-without-blank-lines.txt

Extended reading

More about “find” command can be found here: How to: Use “find” command in Linux (Debian, Ubuntu, Kali Linux, CentOS, RHEL/RedHat etc.)

Other techniques related to grep can be found here: How to: Search in Linux, How to: Use grep command, How to: Use grep to search

More on whereis, which commands: Linux, Ubuntu etc. How to find where the program is installed


Basic/Common Special symbols/Special characters in Linux

Home Directory ~

# Back to home directory
cd ~
 
# Change to sub directory within home directory
cd ~/Desktop

Current Directory .

ls -al
ls -al

. in above image means current directory

# Run script.sh in current directory
./script.sh

Parent Directory ..

cd ..
cd ..
cd ..
# Change to /test/ folder in parent folder directory
cd ../test/

Path Separator, System root folder /

ls /etc
# Change to system root folder
cd /

Comment #

#Comments are ignored by Bash shell
Comment
Comment

We can also comment part of the string from variable

# Define variable
test_string="abc def"
 
# echo the variable with abc being commented out
echo ghi ${test_string#abc}
 
# echo full variable
echo $test_string
Comment part of the string/variable
Comment part of the string/variable

Single Character Wildcard ?

? Can be used for this purpose

ls file?.txt
ls file?.txt
ls file?.txt

Since file.txt doesn’t have any characters right after file, it is not in the result.

To match exactly how many characters with ?, we use corresponding number of ?

ls ????.txt
ls ????.txt
ls ????.txt

Wildcard *

Match any character including space

ls file*
ls file*
ls file*

Match any type of files

ls file.*

Character Set Wildcard []

Match at least one of the characters in the []

ls file0[123].txt
ls file0[123].txt
ls file0[123].txt
ls file[012][012].txt
ls file[012][012].txt

Shell Command Separator (Run till the last one anyway) ;

command 1; command 2; command 3
command 1; command 2; command 3
command 1; command 2; command 3

When using Shell Command Separator “;” no matter the previous command succeeded or not, it will run till the last command

Shell Command Separator (Stop if there is error/failed) &&

command 1 && command 2 && command 3
command 1 && command 2 && command 3
command 1 && command 2 && command 3

Background Process &

Add & behind the command to run the command in the background

command &
Run the command in the background
Run the command in the background

1709 is the process ID of this background task

Input Redirection <

command < file
sort test file
sort test file
wc test
 
wx < test

(< does not display source filename)

Output Redirection >

ls > ListOfFiles.txt
 
# To read the file again
cat ListOfFiles.txt

It can be used with stderr, stdin, stdout (See bottom of this page)

cat test.txt 2> err.txt
Use with stderr
Use with stderr

Pipe |

command 1 | command 2 | command 3
cat test | grep [Aa] | sort -r
Demo or pipe
Demo or pipe

1 Use cat to read test, pip to grep command

2 Use grep to filter the test, only left with text including A and a, pipe to sort command

3 Use sort to reverse sort the text

Pipeline logical NOT and History Operator !

[ ! -d ./testfolder ] && echo "Folder testfolder does not exist"

[ ! -d ./testfolder ]: Check if the folder named testfolder exists

If does not exist, echo the text Folder testfolder does not exist

Run history command

!number
 
# e.g.
!210
Run history command
Run history command
# Run last command
!!
Run last command
Run last command

Variable Expressions $

In Bash shell, $ usually means variables

We can use echo to view the values of the variable

echo $PATH
 
echo $USER
 
echo $HOME
Show values in variables
Show values in variables

We can define variables in following ways

year=2020
MyName=Fred
Define variable

We can use {} to perform other advanced manipulation of text

# Define variable
string=12345qwert
 
# Output the string
echo ${string}
 
# Output text begin from index of 3 (Begin from 0)
echo ${string:3}
 
# Output 3 characters begin from index 0
echo ${string:0:3}
 
# Output 2 characters begin from index 2
echo ${string:2:2}

Quoting Special Characters “” ”

Use “” to stop special character functions (But not $)

echo "$string"
Double quotes
Double quotes

Use single quotes ” to disable all special character’s function

echo '$string'
Single quotes
Single quotes

We can also use backslash \ to prevent the following character to be functioning as a special character

echo "\$string"
Backslash
Backslash

Extend Reading

More on redirection, pipeline,stdin,stdout,stderr | Linux – Basics, Useful Terminal commands and Basic File manipulation, (QuickStart)

More on flow control, if else, loop, variable Linux Bash/Shell simple, basic flow control


Powerful Linux Interactive shell

fish (friendly interactive shell) is a smart and user-friendly command line shell for Linux, macOS, and the rest of the family.

Autosuggestions

Autosuggestion Thumbnail

fish suggests commands as you type based on history and completions, just like a web browser. Watch out, Netscape Navigator 4.0!

Glorious VGA Color

Colors Thumbnail

fish supports 24 bit true color, the state of the art in terminal technology. Behold the monospaced rainbow.

Sane Scripting

Scripting Thumbnail

fish is fully scriptable, and its syntax is simple, clean, and consistent. You’ll never write esac again.

Web Based configuration

Web Config Thumbnail

For those lucky few with a graphical computer, you can set your colors and view functions, variables, and history all from a web page.

Man Page Completions

Man Page Completions Thumbnail

Other shells support programmable completions, but only fish generates them automatically by parsing your installed man pages.

Works Out Of The Box

Works Out of the Box Thumbnail

fish will delight you with features like tab completions and syntax highlighting that just work, with nothing new to learn or configure.

fish can be installed easily on most Linux distros with their default package manager.

Linux

# Debian/Ubuntu/Kali Linux etc.
sudo apt install fish
 
# RHEL/CentOS/Fedora
sudo dns install fish
or, for older version
sudo yum install fish
 
# Archlinux
pacman -S fish
 
# gentoo Linux
emerge fish
 
# void-Linux
xbps-install fish-shell
 
# NixOS
nix-env -i fish
 
# Guix
guix package -i fish
 
# Solus
eopkg install fish
 
# Hombrew
brew install fish

BSD

# FreeBSD
pkg install fish
 
# OpenBSD
pkg_add fish

Windows

# Cygwin
fish is available in setup, in the Shells category.
 
# Windows Subsystem for Linux
sudo apt install fish
or
depend on the Linux distro you've chose, refer to the above "Linux" part to find correct command to use
 
# MSYS2
pacman -S fish

masOS

# Homebrew
brew install fish
 
# MacPorts
sudo port install fish
 
# Installer
https://github.com/fish-shell/fish-shell/releases/download/3.1.0/fish-3.1.0.pkg
 
10.6+: Installs to /usr/local/

Bonus

  • To use, type fish in the terminal then hit Enter key

To check fish version

echo $FISH_VERSION

HTML version help document

help

To switch default shell to fish

sudo chsh -s /usr/bin/fish

To switch back to default bash shell

sudo chsh -s /bin/bash

(If your default shell is zsh)

sudo chsh -s /usr/zsh

How to: Check/Change/Set/Modify Linux (Debian/Ubuntu/Kali Linux) date/time/timezone etc. (and Calculate past/future date/time) in Terminal

Check/Calculate time

Show current time

date
date
date

Calculate past/future time

date --date="1 day ago"
 
date --date="2 hours ago"
 
date --date="3 days"
 
date --date="2 hours"
Calculate dates/time
Calculate dates/time

timedatectl
 
timedatectl status
timedatectl
timedatectl
timedatectl status
timedatectl status

Show/Change timezone

Show timezone

timedatectl list-timezones

Set timezone

timedatectl set-timezone Africa/Abidjan

Change time by using “timedatectl”

(HH:MM:SS, in 24 hour format)

sudo timedatectl set-time 00:00:00
Use timedatectl set-time to change time
Use timedatectl set-time to change time

Change time by using “date”

(HH:MM:SS, in 24 hour format)

sudo date +%T -s "23:00:00"

(12 hour format)

sudo date +%T%p -s "2:00:00AM"
 
sudo date +%T%p -s "2:00:00PM"

Change date

Set the date and time to 03 Feb 2001, 01:00:00

sudo date --set="20010203 01:00:00"
 
sudo timedatectl set-time '2001-02-03 01:00:00'

Set date

sudo timedatectl set-time 2001-02-03
 
sudo date --date="2001-02-03"

Create custom date format (+)

sudo date +"Year : %Y Day : %d Month : %m"
 
# Output
Year : 2001 Day : 03 Month : 02
 
sudo +%D
 
# Output
02/03/01
 
sudo date +"%a %b %d %y"
 
# Output
Sat Feb 03 01
 
sudo date +"%A %B %d %Y"
 
# Output
Saturday February 03 2001
 
sudo date +"%A %B %d %Y %T"
 
# Output
Saturday February 03 2001 00:27:30
 
sudo date +"%A %B-%d-%Y %c"
 
# Output
Saturday February-03-2001 Sat 03 Feb 2001 00:28:17 EST

%D: Year/Month/Day format.

Show CMOS Time

sudo hwclock
hwclock
hwclock

How to: Switch Desktop Environments for Kali Linux easily

By default, Kali Linux uses XFCE as desktop environment, it is lightweight and quick.

Sometimes we want to switch to other desktop environment like GNOME, here is how (Switch to other desktop environment will have similar steps)

We can Install GNOME desktop environment with tasksel. (Easier)

1 Launch tasksel

sudo tasksel
sudo tasksel
sudo tasksel

2 Make sure “GNOME” is selected (Use Up/Down Arrow keys to navigate through the list, Space key to select/deselect)

tasksel
tasksel

3 Use tab key to highlight “<Ok>”, then hit “Enter” key to confirm and install GNOME

tasksel - OK
tasksel – OK

4 After the installation is done, we need to use following command to change default desktop environment

sudo update-alternatives --config x-session-manager
sudo update-alternatives --config x-session-manager
sudo update-alternatives –config x-session-manager

5 Enter correct number which represents corresponding desktop environments (In this case we enter 1, then press Enter key again)

We select GNOME desktop environment
We select GNOME desktop environment

6 We reboot the system

sudo reboot

7 Login to the system

8 Now we can see Kali Linux is using GNOME as desktop environment

sudo update-alternatives --config x-session-manager
sudo update-alternatives –config x-session-manager

To switch back, we just simply repeat step 4 to step 7 again, but use different number, e.g. number for xfce4 is 2 this time in above image.

To switch to other desktop environments, the steps are very similar, we just need to install different desktop environment first then make sure selecting the correct desktop environment for x-session-manager.


How to: Upgrade Roundcube webmail easily with terminal/command

Roundcube is an open source web/online MUA (mail user agent)

Note!: Don’t forget to change the download link and folder name for wget and Install/Update (Step 2 and 4)

#1 Switch to /tmp directory
cd /tmp
 
#2 Download the package with wget
wget https://github.com/roundcube/roundcubemail/releases/download/1.4.3/roundcubemail-1.4.3-complete.tar.gz
 
#3 Extract the package
tar xf roundcubemail-*.tar.gz
 
#4 Install/Update
./roundcubemail-1.4.3/bin/installto.sh /destinationFolder/roundcube

Extended Reading

MUA (mail user agent) Is used for users to read, compose, and send email. Examples of MUAs are Roundcube, SquirrelMail, pine, Microsoft Outlook etc.

MTA (mail transfer agent) Is used for the transport, delivery, and forwarding of email. Examples of MTAs like SMTP servers are POSTFIX, sendmail etc.


How to: Run Linux commands with time limit/timeout (Kill process/command after some time)

Sometimes we want to stop or kill the command after a period of time, so that we don’t get stuck with that command and wasting resources etc. To specify timeout or time limit for Linux command, we can use timeout command

Command Usage/Parameters

timeout [OPTION] DURATION COMMAND [ARG]...

DURATION is integer or floating point with unit

s: Seconds (Default)

m: Minutes

h: Hours

d: Days

Without units appended, by default it is considered as seconds.

If the DURATION is 0, the timeout is disabled.

Basic Usage

Timeout ping command after 3 seconds

timeout 3 ping 127.0.0.1
timeout 3 ping 127.0.0.1
timeout 3 ping 127.0.0.1

Timeout ping command after 3 minutes

timeout 3m ping 127.0.0.1

Timeout ping command after 3 days

timeout 1d ping 127.0.0.1

Timeout ping command after 3.2 seconds

timeout 3.2s ping 127.0.0.1

Send specific signal after timeout

By default if signal is not specified, timeout command will use “SIGTERM” signal after timeout. We can use -s (-signal) switch to specific which signal to send after timeout

e.g. Send SIGKILL signal to ping command after 3 seconds

sudo timeout -s SIGKILL 3s ping 127.0.0.1
sudo timeout -s SIGKILL 3s ping 127.0.0.1
sudo timeout -s SIGKILL 3s ping 127.0.0.1

We can use the name of the signal or the number of the signal

e.g. We can use 9 as SIGKILL to achieve same result

sudo timeout -s 9 3s ping 127.0.0.1
sudo timeout -s 9 3s ping 127.0.0.1
sudo timeout -s 9 3s ping 127.0.0.1

To list all acceptable signal, we can use kill -l to find out

kill -l
[email protected]:~# kill -l
 1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL       5) SIGTRAP
 6) SIGABRT      7) SIGBUS       8) SIGFPE       9) SIGKILL     10) SIGUSR1
11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM
16) SIGSTKFLT   17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ
26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR
31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3
38) SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7
58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2
63) SIGRTMAX-1  64) SIGRTMAX
kill -l
kill -l

Stop frozen process

SIGTERM, the default signal can be ignored by some processes, thus the program will keep running. To make sure the process is killed, we can use -k (–kill after) switch with specified time. When the time limited reached, force to kill the process.

e.g. Let the shell script run for 2 minutes, if it did not exit, then kill after 5 seconds

timeout -k 5s 2m sh test.sh

By default the timeout command will run in background, if we want to run it in foreground, refer to following example

timeout --foreground 2m ./test.sh

timeout help

Usage: timeout [OPTION] DURATION COMMAND [ARG]...
  or:  timeout [OPTION]
Start COMMAND, and kill it if still running after DURATION.
Mandatory arguments to long options are mandatory for short options too.
      --preserve-status
                 exit with the same status as COMMAND, even when the
                   command times out
      --foreground
                 when not running timeout directly from a shell prompt,
                   allow COMMAND to read from the TTY and get TTY signals;
                   in this mode, children of COMMAND will not be timed out
  -k, --kill-after=DURATION
                 also send a KILL signal if COMMAND is still running
                   this long after the initial signal was sent
  -s, --signal=SIGNAL
                 specify the signal to be sent on timeout;
                   SIGNAL may be a name like 'HUP' or a number;
                   see 'kill -l' for a list of signals
  -v, --verbose  diagnose to stderr any signal sent upon timeout
      --help     display this help and exit
      --version  output version information and exit
DURATION is a floating point number with an optional suffix:
's' for seconds (the default), 'm' for minutes, 'h' for hours or 'd' for days.
A duration of 0 disables the associated timeout.
If the command times out, and --preserve-status is not set, then exit with
status 124.  Otherwise, exit with the status of COMMAND.  If no signal
is specified, send the TERM signal upon timeout.  The TERM signal kills
any process that does not block or catch that signal.  It may be necessary
to use the KILL (9) signal, since this signal cannot be caught, in which
case the exit status is 128+9 rather than 124.
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation at: <https://www.gnu.org/software/coreutils/timeout>
or available locally via: info '(coreutils) timeout invocation'