| Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting | ||
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| Prev | Chapter 16. I/O Redirection | Next |
The exec <filename command redirects stdin to a file. From that point on, all stdin comes from that file, rather than its normal source (usually keyboard input). This provides a method of reading a file line by line and possibly parsing each line of input using sed and/or awk.
Example 16-1. Redirecting stdin using exec
#!/bin/bash # Redirecting stdin using 'exec'. exec 6<&0 # Link file descriptor #6 with stdin. exec < data-file # stdin replaced by file "data-file" read a1 # Reads first line of file "data-file". read a2 # Reads second line of file "data-file." echo echo "Following lines read from file." echo "-------------------------------" echo $a1 echo $a2 echo; echo; echo exec 0<&6 6<&- # Now restore stdin from fd #6, where it had been saved, #+ and close fd #6 ( 6<&- ) to free it for other processes to use. # # <&6 6<&- also works. echo -n "Enter data " read b1 # Now "read" functions as expected, reading from normal stdin. echo "Input read from stdin." echo "----------------------" echo "b1 = $b1" echo exit 0 |