Difference between revisions of "Opening the file descriptors for reading and writing"

From Linux Shell Scripting Tutorial - A Beginner's handbook
Jump to navigation Jump to search
(Created page with 'Bash supports the following syntax to open file for both reading and writing on file descriptor: <pre>exec fd<>fileName</pre> * File descriptor 0 is used if fd is not specified. …')
 
m
Line 17: Line 17:
 
echo "Anger leads to hate. Hate leads to suffering." >&3
 
echo "Anger leads to hate. Hate leads to suffering." >&3
 
echo "--- Zoda" >&3
 
echo "--- Zoda" >&3
 
# Read the same file using while loop
 
while IFS= read -u 3 -r line
 
do
 
  echo $line
 
done
 
  
 
# close fd # 3
 
# close fd # 3
 
exec 3>&- </source>
 
exec 3>&- </source>
 
[[Category:Redirection]][[Category:Commands]]
 
[[Category:Redirection]][[Category:Commands]]

Revision as of 22:45, 19 September 2009

Bash supports the following syntax to open file for both reading and writing on file descriptor:

exec fd<>fileName
  • File descriptor 0 is used if fd is not specified.
  • If the file does not exist, it is created.
  • This syntax is useful to update file.

Example

Create a shell script called fdreadwrite.sh

#!/bin/bash
FILENAME="/tmp/out.txt"
# Opening file descriptors # 3 for reading and writing
# i.e. /tmp/out.txt
exec 3<>$FILENAME

# Write to file
echo "Today is $(date)" >&3
echo "Fear is the path to the dark side. Fear leads to anger. " >&3
echo "Anger leads to hate. Hate leads to suffering." >&3
echo "--- Zoda" >&3

# close fd # 3
exec 3>&-