Recipe: Playing with file descriptors and redirection

Saving output to a file
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$ echo "This is a sample text 1" > temp.txt


Appending output to a file
==========================
$ echo "This is sample text 2" >> temp.txt

$ cat temp.txt
This is sample text 1
This is sample text 2


Redirecting error using 2> and 2>&1
===================================
$ ls + 2> out.txt


$ cmd 2>&1 output.txt 

$ $ cmd &> output.txt

tee
===
$ ls + 2>&1 |  tee out.txt
$: command not found

$ cat out.txt
$: command not found

Duplicating with tee
====================
$ echo who is this | tee -
who is this 
who is this 

Redirection from file
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$ cmd < file

$ cat < file


Custom file descriptors
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$ exec 4>input.txt # open for writing
$ echo hello >&4 # Concatenate hello to input.txt
$ exec 3<input.txt # open for reading
$ cat <&3 # Reading from descriptor associated file (Similar to Section 2)
hello