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Basic Linux Tutorial

Introduction – What is it? Why to learn? Linux installation directory structures Boot process Run levels in Linux Desktop Environments Different shells BASH Internal and External Commands Basic Linux Commands Important files and directories in Linux Environmental and Shell Variables Command history in Linux Character classes in Linux Text editors vim nano Searching files Creating new files Viewing File Contents File commands File permissions and ownership WildCards (Globbing) in files File compression Directory commands xargs command in Linux Comparing files Searching patterns using grep command Translating the characters using tr command Extracting data using cut command Stream editing using sed command Data extraction and reporting using awk command Sorting the file or string input uniq command in Linux Difference between grep, tr, cut, sed and awk commands Hardware commands Hard disk and memory space commands Working with Processes Managing Jobs Working with cron jobs Service command in Linux Network commands Managing Users and Groups Other Popular commands Standard streams and Redirection Pipes Package Managers in Linux

streams in linux shell

In linux, we have 3 standard streams.
  • Standard input stream – 0 – Keyboard
  • Standard output stream – 1 – Shell terminal display
  • Standard error stream – 2 – Shell terminal display
When we type any characters from the keyboard, it goes into the standard input stream. When program executes and displays output, it is pushed into the output stream (Terminal Display) . Any error information is pushed into the error stream (Terminal Display). But we don’t want input or output to go into standard stream at all times. For example – input required for the program may be available in the file. So instead of reading from the keyboard(standard input stream – 0), we can read it from file itself. Similarly, output generated by the program may be redirected to file stream or any other stream instead of standard output stream (1 – Terminal Display). We have below redirection operators in linux.
 
> – redirects standard output to some file
>> – redirects the output to the file (Appends)
< – redirects standard input to some file
Examples –
 
cat abc.txt > xyz.txt
Above command will copy data from abc.txt to xyz.txt
 
cat abc.txt >> xyz.txt
Above command will copy data from abc.txt and append it into xyz.txt
 
wc -l < xyz.txt
Above command will read data from xyz.txt and print total number of lines in that file. Tee command redirects output to the file as well as sends data in output stream /dev/null is a special device. If you try to to redirect your data in that device, nothing will be stored.

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