script

How to read and write from a file in a Linux bash shell script

I’m currently writing a complicated Linux bash shell script where I need to keep a counter in an external file, and to do so, I need to be able to write to a file and then read from that file.

In short, this is how I write my counter to that file:

# create a variable to represent the filename
COUNTER_FILE="counter.tmp"

# write to the file
echo "0" > $COUNTER_FILE

Later in the code I increment the counter and write it to the file like this:

How to run a Unix shell script from the Mac Finder

If you ever want to create a Unix shell script that you can give to someone else so they can double-click it and run it through the Mac OS X Finder, all you have to do is (a) name the file with the ".command" extension and (b) make it executable. So, just name your Mac/Unix script like this:

ShowProcesses.command

Then make it executable, like this:

chmod +x ShowProcesses.command

You can also leave out the usual #!/bin/sh part on the first line.

Setting the classpath in a Scala script (Scala shell script)

Scala script FAQ: How do I set the CLASSPATH in a Scala shell script?

If you need to set the CLASSPATH when executing a Scala script, use the exec command as shown in the following example:

#!/bin/sh
exec scala -classpath "lib/htmlcleaner-2.2.jar:lib/scalaemail_2.9.1-1.0.jar:lib/stockutils_2.9.1-1.0.jar" "$0" "$@"
!#

As you can see from that code, I'm adding three jar files to my classpath at the beginning of my Scala shell script.

Reading Scala command line arguments

Scala command line FAQ: How do I read command line arguments (args) in a Scala shell script?

If your Scala shell script is very short, and you're not using an object or class declaration -- i.e., you have no main method -- you can access the script's command line arguments through the default args array, which is made available to you by Scala.

For instance, you can create a one-line Scala script named hello.scala like this:

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