Index

• Command interpret history
  • TTY
  • Shell
  • Bash
  • Zsh
• How to "chain" command
  • Flux and piping
  • && AND gate
  • BONUS: || OR gate
• Brace Expansion

Command interpret history

TTY

TTY virtual device in the computer that allow an user to interact with the system

i think ALL command interpreter (Shell, Bash , zsh ...) use TTY to send and recevied command from the system

Shell

Shell is the first command interpreter that appears with first unix systems, created by Thompson Shell in 1971

Bash

(kind default shell) Bash appear first with the first free implementation of GNU/Linux

BASH (aka Bourne Again shell) is an enhanced, compatiable with, version of shell in some later version of sh and on certain Operating system the /bin/sh is link to /bin/bash. so it's barrely the some on purpose

Zsh

ZSH (aka Z-Shell) is an upgrade to bash, it included pulgins themes and many features.

How to "chain" command

Flux and piping

in most Linux distribution command interpreter can redirecte output(1) to input(0) for another programs, with the character |. like so, the following is possible: cat filename | grep "word"

&& AND gate

like piping, it's possible to pipe the error(2)(returned value) to a logic operator instead of |, && is used to do an logic AND, so the previous statement have to return a true to go for the second command, exemple:

gcc -Wall -Werror -Wextra main.c -o main && ./main

two command and one logic operator:

• the first command compile the main.c and output it to main
• the && check if the compilation have been successfully or not
• execute ./main only if the compilation was a success

that prevent to launch a programm that was not changed or just not here

Silent error

you can redirect the stderr fd (2) with the folling exemple

# find command with a lot of errors
bash$ find / -name "*.txt"

# wihtout errors
bash$ find / -name "*.txt" 2>/dev/null

/dev/null is the place were nothing append, you redirect any file descriptor to it and it will accept it

BONUS: || OR gate

let's take the exemple above and to it a condition were the compilation failed:

gcc -Wall -Werror -Wextra main.c -o main && ./main || echo "Compilation Failed"

two command and two logic operator:

• like the exemple the first command compile the main.c
• the && check if the compilation have been successfully or not
• execute ./main only if the compilation was a success
• The || OR check if the previous command was NOT executed :)
• echo command only append if the ./main was NOT executed

juste lil' trick outder u know

Brace Expansion

basisc of lists

list can be crafted with brace seperated with comma

bash$ echo {1,2,3}
> 1 2 3
bash$ echo test_{1,2,3}
> test_1 test_2 test_3
bash

this can be user to rename things

bash$ echo test{,_COMPLETE}
> test test_COMPLETE

bash$ mv test{,_COMPLETE}
# equivalent to mv test test_COMPLETE

bash$ mv test{_COMPLETE,_FINISHED}
# equivalent to mv test_COMPLETE test_FINISHED

bash$ echo test_{1,2,3}{_BONUS,_EXTANDED}
test_1_BONUS test_1_EXTANDED test_2_BONUS test_2_BONUS ...

Search and replace

with brace expansion we can search and replace strings within a variable

# '%' remove from the end
bash$ filename="file.txt"
bash$ echo ${filename%.txt}
> file

# '#' remove from the begin
bash$ filename="file.txt"
bash$ echo ${filename#file}
> .txt

# Search and replace on all the string
bash$ string="long_string_name_with_a_THINGS_i_want_to_remove"
bash$ echo ${string/_THINGS/}
> long_string_name_with_a_i_want_to_remove
bash$ echo ${string/o/}
> lng_string_name_with_a_THINGS_i_want_to_remve