Thursday, February 3, 2011

An SQLite/STDIN Conundrum, Specific to AIX

Hi there!

I'm been playing around with SQlite at work, specifically with trying to get the sqlite3 command line tool to accept stdin instead of a file. Sounds easy enough, on linux you can execute a command like:

echo 'test' | sqlite3 test.db '.import /dev/stdin test'

unfortunately - our machines at work run AIX (5 & 6) and as far as I can tell, there is no equivalent to the virtual file /dev/stdin. I managed to hack together an equivalent command that works on AIX using a temporary file.

echo 'test' | cat - > /tmp/blah ; sqlite3 test.db '.import /tmp/blah test' ; rm /tmp/blah

Now, does it need to use STDIN? isn't this temporary file thing enough? Probably, but I was hoping someone with better unix-fu had a more elegant solution.

note: the data I would like to import is only provided via STDOUT, so that's what the echo 'test' command is all about.

Clarification - I only have control over commands on the Right Hand Side of the pipe shown above. The data is being processed, and then passed to my command via stdin/stdout. the echo 'test' command is illustrative only.

  • If you're actually using Bash and AIX supports process substitution (which I believe is platform dependent), this might work for you:

    Demo:

    cat <(echo 'test')
    

    Your command:

    sqlite3 test.db '.import '<(echo test)' test'
    
    mikfreedman : the echo test bit unfortunately isn't another unix command line tool - it's some random program that communicates via stdin/stdout, but has a convoluted execution framework that wouldn't allow it to be called that way, if that makes sense.
    Dennis Williamson : @mikfreedman: I don't understand. If it can be called in a pipeline, it can be called using process substitution. Also, in your second command in your question why use `cat -`? Why not `echo 'test' > /tmp/blah`?
    mikfreedman : in the program I am using, I can enter a unix command that the program will write to, the only requirement is this program can only write to STDOUT.. so, it's arriving at my arbitrary command via a pipe, but the order must be as I described. For reference the program I am using is Infosphere DataStage.

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