BASH IO redirection

IO redirection:

IO redirection will capture a file , commands, program, scripts’s output, and send it to another file, commands and scripts.

Background: every script has three standard file discriptor:

       stdin: standard input

       stout: standard output

       stderr: standard error output

IO redirection example:

Output redirection

> file: output to the target file, it will overwrite the file content.

>> file: output to the target file, it will append the content at the end of the file

>| file : override the file even with noclobber option

stderr redirection

2>newfile: redirect the stderr to the newfile, for example: ls –al zz 2>newfile.

              If no file matched. The error msg will be written to newfile

stdin redirection

script < file: use file as my stdin instead of default stdin

<<delimiter – redefine the delimiter

For example

#cat > mytest<<GO

>this is my test

>it is ok

>let’s GO

>GO

#cat mytest

this is my test

it is ok

let’s GO

block redirction

> outputfile and < input file. It can used to change the stdin or stdout temporarry.