2.1 KiB
Basics
Basics of the Linus Shell
Streams
The linux shell (this will usually be bash) works using different streams
The main three streams that are used on the command line are STDIN (Standard input), STDOUT (Standard output), STDERR (Standard Error)
STREAM ID STREAM NAME STREAM USE
0 STDIN Used to send input to the program
1 STDOUT Used to receive output from the program
2 STDERR Used to receive errors from the program
Standard Input
Standard input is how we send input to an application it is also how we interact with the command line shell (Usually bash)
Whenever a linux program asks for input this is sent to the program using the STDIN stream
The STDIN stream can also be refrenced by the '-' char in a command line application cat - will print what comes into STDIN (The terminal)
One thing that makes the linux command line so powerfull is the suite of commands that is provided all work using STDIN, STDOUT and STDERR you can pipe information from one stream to another (i.e the STDOUT from one program can be in STDIN to another)
Input Redirection
You can use redirection to send information to a program using the '<' symbol i.e cat < file this will push the contents of 'file' to cat using STDIN
Standard Output
Standard output is how we get the output from a program, usually this is printed directly to the terminal
Output Redirection
You can redirect the STDOUT of a application is a few ways you can use the '>' symbol to push the information from the programs output and saves it in a file for example ls > filelist will take the output of ls and saves it in the filelist file
You can also redirect the STDOUT of one program to another programs STDIN using the '|' symbol doing this you can combine muliple programs in different ways
For example you can use ls -alh | grep filename this will list the files in the current directory and then passes the STDOUT to the STDIN for grep, this causes grep to use the output of ls as the input data to work with so the output of ls is searched for the string 'filename'