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bashm4

M4: How to drop leading whitespace from script followed by file?

If I have an m4 script with many commands:

define(this, that)
define(or,this)
define(other,thing)

And I call: 

$: m4 script.m4 my_file

The output is:

# N newlines for the N commands in the script
# first line of my file

Is it possible to suppress the N newlines resulting from the script read-in when calling m4, or do I have to wrap this in some set of calling commands (like sed or grep)?

Solution

  • You can use the dnl macro to delete new lines for defines. E.g. from this tutorial:

    The define macro itself – including its two arguments – expands to an empty string, that is, it produces no output. However the newline at the end of the AUTHOR definition above would be echoed to the output. If a blank line added to the output is a problem then you can suppress it using the “delete to newline” macro:

     define(AUTHOR, W. Shakespeare)dnl

    There is no space between the end of the macro and the dnl: if there were then that space would be echoed to the output.