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user1091344
Asked: 2013-12-29 02:27:06 +0800 CST

Use logger in shell script

  • 772

How can I use logger in a shell script?

If I run

ntpd -qnp pool.ntp.org 2> >(logger)

in console, it works as expected.

If I put it into a shell script

#!/bin/sh
ntpd -qnp pool.ntp.org 2> >(logger)

I get following error:

line 2: syntax error: unexpected redirection
exited with code 2

What is wrong in the shell script?

linux

4 Answers

  1. Best Answer

    The shebang is correct as both #!/bin/sh and #!/bin/bash can be used*, however, IIRC, you should use pipes not redirect for logger as it's a program not a file.

    Try this script:

    
#!/bin/sh
ntpd -qnp pool.ntp.org 2>&1 |logger

    *If you use #!/bin/sh for your scripts, they are supposed to be posix compliant, ie run well on solaris and AIX. If ever you use some bash specific features, #!/bin/bash have to be used because there's no more portability.

    • 6

  2. What's wrong is that you're using bash-ism's while your hash-bang is saying /bin/sh. Change it to #! /bin/bash and it will work.

    • 2

  3. I actually had to check what the line ntpd -qnp pool.ntp.org 2> >(logger) does:

    1. Run ntpd -qnp pool.ntp.org
    2. Redirect its stderr using 2> to ... where exactly? Well....
    3. >(logger)
      1. Creates a named pipe (see Mechanism), call it /dev/fd/pipe100
      2. Starts process logger reading its STDIN from that pipe
      3. Substitutes the name /dev/fd/pipe100 into the command
    4. ...thus running ntpd -qnp pool.ntp.org 2> /dev/fd/pipe100
    5. ...while process logger reads from that pipe: logger < /dev/fd/pipe100

    The above should work nicely in bash.

    However, I tried to run it using "sh" explicitly, which yields:

    script.sh: line 3: syntax error near unexpected token `>'

    So, as the other commenters noted, you are probably not using the bash here.

    Indeed, Busybox uses the Almquist Shell by default.

    • 2

  4. Most likely you have a different shell with /bin/sh than your default shell (probably bash)

    To check try to run the script with /bin/sh ./yourscript or put the same shell as $SHELL into your script

    Which shell is used for /bin/sh is probably distribution dependent plus if you are on Solaris, it is something completely different.

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