aslamnotes

Shell

2 min read

Definitions

A Shell is a computer program often represent itself as a computer program via GUI or CLI that provides you with a interface between the user and the OS.

  • CLI shells (bash, zsh, PowerShell) → thin. They parse input and launch programs.
  • GUI shells (GNOME Shell, Windows Explorer) → thicker. They manage windows, panels, compositors, widgets.

Interactive vs Non-interactive shell

Interactive: As the term implies: Interactive means that the commands are run with user-interaction from keyboard. E.g. the shell can prompt the user to enter input.

Non-interactive: the shell is probably run from an automated process so it can’t assume, it can request input or that someone will see the output. E.g., maybe it is best to write output to a log file.

Login vs Non Login shells

Login: Means that the shell is run as part of the login of the user to the system. Typically used to do any configuration that a user needs/wants to establish his work environment.

Non-login: Any other shell run by the user after logging on, or which is run by any automated process which is not coupled to a logged in user.

GNOME Shell, Windows, OSx are graphical shells that is configured to start when I boot the system, so it makes it a login shell.

Viewing file sizes

The du command display the file size or “disk usage” of the given argument

du -sh file

s - each entry for specified file, if not each file in the directory or printed h - human readable

The same can be achieved via long list ll -lh

Archiving Files with Tape Archive

Create a tar ball

tar -cf test.tar file1 file2

Create a tar ball with gzip

tar -zcf test.tar file1 file2

List the files in a tarball (or —list)

tar -tf test.tar

Compressing files

gzip, bzip2, xz - Popular compression utilities gunzip, bunzip2, unxz - Un -zip them zcat, bzcat, xzcat - Read without uncompressing

Searching files and directories

Find the files with name city.txt locate city.txt

search within a file (os.stdint, pipe, regular files) grep -r to search within a directory recursively

grep -w to search a word

Redirect IO

redirect stdin > or 1> redirect stderr 2> redirect stdout 3>

Graph View