Every now and then I have a need to redirect all output, both standard and error, within a shell script (bash) to a file. There are two ways — the obvious
beginners’ one and the elegant
gurus’ one.
For starters let’s have a very simple script
test.sh that generates both standard output (
stdout) and error message (
stderr):
#!/bin/sh
echo "Going to run /non/existent"
/non/existent
That will produce an expected result when run:
~$ ./test.sh
Going to run /non/existent
./test.sh: line 4: /non/existent: No such file or directory
~$
Now the question is
how to redirect both messages into a logfile? The poor man’s approach is to create a wrapper-script
test-wrapper.sh:
#!/bin/sh
exec ./test.sh > test.log 2>&1
Running that will send all the output into
test.log logfile:
~$ ./test-wrapper.sh
~$ cat test.log
Going to run /non/existent
test.sh: line 4: /non/existent: No such file or directory
~$
Works a treat, but do we
really need two scripts to solve such a simple problem? Of course we don’t. Let’s modify
test.sh this way:
#!/bin/sh
exec > test2.log
exec 2>&1
echo "Going to run /non/existent"
/non/existent
Run it and enjoy the output redirected to a log file
test2.log:
~$ ./test.sh
~$ cat test2.log
Going to run /non/existent
./test.sh: line 7: /non/existent: No such file or directory
~$
Voilà, here you go. Self contained script that sets up the redirection internally. No need for stupid wrappers anymore ;-)
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