I’ve been trying to optimise some Neo4j import queries over the last couple of days and as part of the script I’ve been executed I wanted to redirect the output of a couple of commands into a file to parse afterwards.
I started with the following script which doesn’t do any explicit redirection of the output:
#!/bin/sh ./neo4j-community-2.2.3/bin/neo4j start
Now let’s run that script and redirect the output to a file:
$ ./foo.sh > /tmp/output.txt Unable to find any JVMs matching version "1.7". $ cat /tmp/output.txt Starting Neo4j Server...WARNING: not changing user process [48230]... waiting for server to be ready.... OK. http://localhost:7474/ is ready.
So the line about not finding a matching JVM is being printed to stderr. That’s reasonably easy to fix:
#!/bin/sh ./neo4j-community-2.2.3/bin/neo4j start 2>&1
Let’s run the script again:
$ ./foo.sh > /tmp/output.txt $ cat /tmp/output.txt Unable to find any JVMs matching version "1.7". Starting Neo4j Server...WARNING: not changing user process [47989]... waiting for server to be ready.... OK. http://localhost:7474/ is ready.
Great, that worked as expected. Next I extended the script to stop Neo4j, delete all it’s data, start it again and execute a cypher script:
#!/bin/sh ./neo4j-community-2.2.3/bin/neo4j start 2>&1 rm -rf neo4j-community-2.2.3/data/graph.db/ ./neo4j-community-2.2.3/bin/neo4j start 2>&1 time ./neo4j-community-2.2.3/bin/neo4j-shell --file foo.cql 2>&1
Let’s run that script and redirect the output:
$ ./foo.sh > /tmp/output.txt Unable to find any JVMs matching version "1.7". real 0m0.604s user 0m0.334s sys 0m0.054s $ cat /tmp/output.txt Unable to find any JVMs matching version "1.7". Another server-process is running with [50614], cannot start a new one. Exiting. Unable to find any JVMs matching version "1.7". Another server-process is running with [50614], cannot start a new one. Exiting. +---------+ | "hello" | +---------+ | "hello" | +---------+ 1 row 4 ms
It looks like our stderr -> stdout redirection on the last line didn’t work. My understanding is that the ‘time’ command swallows all the arguments that follow whereas we want the redirection to be run afterwards.
We can work our way around this problem by putting the actual command in a code block and redirected the output of that:
#!/bin/sh
./neo4j-community-2.2.3/bin/neo4j start 2>&1
rm -rf neo4j-community-2.2.3/data/graph.db/
./neo4j-community-2.2.3/bin/neo4j start 2>&1
{ time ./neo4j-community-2.2.3/bin/neo4j-shell --file foo.cql; } 2>&1$ ./foo.sh > /tmp/output.txt $ cat /tmp/output.txt Unable to find any JVMs matching version "1.7". Another server-process is running with [50614], cannot start a new one. Exiting. Unable to find any JVMs matching version "1.7". Another server-process is running with [50614], cannot start a new one. Exiting. Unable to find any JVMs matching version "1.7". +---------+ | "hello" | +---------+ | "hello" | +---------+ 1 row 4 ms real 0m0.615s user 0m0.316s sys 0m0.050s
Much better!
| Reference: | Unix: Redirecting stderr to stdout from our JCG partner Mark Needham at the Mark Needham Blog blog. |
