Shell Redirection with Exec command in Unix / Linux
Lets see an example to perform Shell Redirection with Exec
In Unix shells exec is a builtin command. Here is how to check if a command is a shell builtin.
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$ builtin exec $ echo $? 0 |
The $? when evaluated by the shell results in the exit status of the previous command. A zero return value indicates that the command executed successfully. Execute the same set of commands above, but with builtin ls and see what happens.
Back to exec, it can redirect input and output of the current shell when executed without a command.
Standard output redirection:
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$ exec > output # the standard output is redirected to file foo $ ls # output of ls is written to file foo |
Standard error redirection:
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exec 2> error # the standard error is redirected to file error $ ls no-such-file # output is written to file error $ cat error > /dev/tty # prints contents of file error to terminal |
So, exec is useful when writing a shell script that needs to log output of commands to different files.
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$ exec 3>web.log # open web.log for writing using file descriptor 3 $ exec 4>uptime.log # open uptime.log for writing using file descriptor $ curl google.com >& 3 # the '>& 3' syntax redirects standard out to fd 3 $ uptime >& 4 |
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About Author
manju
I Manjunath is a self confessed addict of Java and a strong supporter of OpenSource Technologies. I live in Bangalore, India.