Thursday, January 02, 2014

GNU-Linux bash shell commands


Linux is the kernel of the operating system on top of which other programs are built. A detailed list of GNU core utilities is available under the command :
info coreutils

 Files 

determine file type and encoding
file filename
list a directory
ls
ls -R #list subdirectories recursively
ls -lh #sizes in human readable format
Find files in subdirectories of the current directory (Quotes are requited to prevent shell command expansion).
find . -name "*.pdf"
find . -mtime 0 # modified in the last 24 hours
Find files in the whole system
locate filename

File and folder compression

Decompress a file
 gunzip file.gz
How do I compress a whole directory?
tar -zcvf archive-name.tar.gz directory-name
Where
  • -z: Compress archive using gzip program
  • -c: Create archive
  • -v: Verbose i.e display progress while creating archive
  • -f: Archive File name
To extract content from the archive in the current directory
tar -zxvf archive-name.tar.gz

Rename files

For example to rename all upper-case .JPG extension into lower-case .jpg extension.
rename 's/\.JPG$/\.jpg/' *.JPG
Change file permission:
chmod a=rwx filename
chmod 777 filename 
Change file permissions recursively:
chmod 755 directoryname
Chmod instructions can be given with characters or numbers, chmod 777 or chmod a=rwx is a question of preference.
  • Some prefer 755 over 777 because giving write access to group and other users could be a security risk. 755 leaves read and execute rights to groups and other users. 755 is visible as "rwxr-xr-x" in ls -l. 
  • The default for document files on Debian seems to be chmod 644, visible as "-rw-r--r--" in ls -l.

Text files

Count the number of lines in a file
wc -l filename.txt
Count occurrences of a word in a file
grep -roh word filename.txt  | wc -w
Remove duplicated lines from a file
awk '!a[$0]++' input.txt
Search with Grep
 grep "text" file.txt
Awk tutorial, for example  filter a large file for lines that have a third field (product code) starting with 44, keep the header line:
awk -F, '$3 ~ /^44/||NR==1' nc201501.dat|less
Regexp match begining of and end of line with ^ and $.

Follow the end of a log file as it is written 
tail -f

Manipulate strings in files

Replace strings
first="I love Suzy and Mary"
second="Sara"
first=${first/Suzy/$second}
Replace strings with sed

sed -i  's/pattern/replacement/g' bli.txt
sed -i  's/^.*\://g' input_file.txt # edit file in place
grep EMAIL input_file.txt |sed  's/^.*\://g' > output_file.txt
Replace strings with perl in a git repository

git grep -lz 'readcsvfromgauss'| xargs -0 perl -i'' -pE "s/readcsvfromgauss/readcsvfromgauss0/g"

PDF files

Commands based on the poppler library for PDF manipulation.
Search a text pattern in all PDF files present in a directory:
pdfgrep pattern *.pdf
 Merge multiple PDF into one:
pdfunite in-1.pdf in-2.pdf in-n.pdf out.pdf
Alternatively, pdftk can be used to merge PDF files
pdftk input1.pdf input2.pdf cat output output.pdf

Videos and audio

Install youtube-dl using pip:
 sudo pip install --upgrade youtube_dl
Download a video from youtube :
youtube-dl video_url
Download only the audio in an .mp3 format
youtube-dl --extract-audio --audio-format mp3 video_url

Users

Check your user id
id 
What group do you belong to as a user
groups
Add a user to the super users
adduser username sudo
That user needs to re-log into the shell for the change to take effect.
Add a new user
useradd username
Set a password for the new user
passwd username
Delete a user
userdel username
Show all users
getent passwd
Show all groups
getent group

System

OS release
less /etc/os-release
Disk usage
du -h
Display available space on drives
df -h
Display available RAM memory
less /proc/meminfo

Install a program
sudo apt-get install
 System name
uname -a
file /sbin/init
hostname -f
Start and quit a super user session
su
exit
Last time the system was started
last reboot 
last

Job handling

List
jobs
Bring a job to the foreground
fg job_number
Run a job in the background. A command followed by an & will run in the background.

Stop a job
CTRL ^ Z
Quit a job
 CTRL ^ C
Kill a malfunctionning program:
kill process_id
Find a program id with:
ps aux
Kill a graphical program, by clicking on it:
 xkill

Users

Create a new user
adduser user_name
Temporary log in as that user
su user_name
Delete a user
userdel user_name

Secure shell

log into a remote machine
ssh user@remote_machine
Copy a local file to a file on the remote machine
scp local_file_name user@remote_machine:path_to_file/file_name
Copy a file from the remote machine to a local file
scp user@remote_machine:path_to_file/file_name  local_file_name
Copy a full directory (dmouraty) from the remote machine:
 scp -rp user@dest:/path destdirectory

Alias

alias ll="ls -lh"

Based on how can i sort du-h output by size
alias du='du -hd1 | sort -h -r'

You can place those commands in your ~/.bashrc to create a permanent alias.
bashrc:
"You may want to put all your additions into a separate file like ~/.bash_aliases, instead of adding them here directly."

.bash_profile and .bashrc

These are places where a user can turn of the system BEEP :
setterm -blength 0
.bash_profile is executed on login shell, when you login in another tty or when you access a system through ssh. .bashrc is executed on non-login shells when you open a terminal window in Gnome.

Debian Dotfiles
"Now, since bash is being invoked as a login shell (with name "-bash", a special ancient hack), it reads /etc/profile first. Then it looks in your home directory for .bash_profile, and if it finds it, it reads that."
[...] "You may have noted that .bashrc is not being read in this situation. You should therefore always have command source ~/.bashrc at the end of your .bash_profile in order to force it to be read by a login shell.  "
In .bashrc a user can set environment variables, define alias (see above).

Keyboard

bash french blogger recommended a simple shell command to change keyboard layout :
sudo loadkeys fr
fr-keyboard on Debian wiki for a more permanent system configuration and use in GUI apps. Switching between keyboads can then be done with:
setxkbmap de
setxkbmap fr

Information about the system

  • cat /proc/meminfo
  • cat /proc/cpuinfo
  • cat /etc/debian_version
  • lsb_release -a

Shortcuts

Keyboard shortcuts for bash  for example Ctrl+A to go to the beginning of a line.

Documentation

No comments: