How can I specify how far/deep the 'file' command should search in a file to locate a match on a "search" definition ?
I am trying to create a universal specification in "/etc/magic" for multi-flavoured Prolog, so that I could do mass-transformation of imported predicate libraries for re-targeting to my personal environment for a project.
Having reviewed a number of the "target" files, I believe I would need to search within the first 3K characters of a file for this to be deemed reasonably successful as an approach.
So far I've tried these 2 flavours/definition, with no success:
[1] 0 search/3072 [Pp][Rr][Oo][Ll][Oo][Gg] Prolog Predicate File (ISO-Compliant Prolog), ASCII text
and
[2] 0 search [Pp][Rr][Oo][Ll][Oo][Gg] Prolog Predicate File (ISO-Compliant Prolog), ASCII text
This second one is successful but only if the pattern is found in the first line of the file.
Also, I tried the following definitions:
[3] 0 search :- Prolog Predicate File (Non-Specific :-)
and
[4] 0 string % Prolog Predicate File (Non-Specific %), ASCII text
However, when I enter either of [3] or [4], below the entry for line [2], these seem to override the effectiveness of [2]. Also, for some reason, regardless of order of precedence in the file, [3] seems to "overcome" any instance that, in my view should match up with [4].
This leads me to the question: How to tell the "file" command to exit on the first match encountered in my magic file and report that?
I have also defined this initial set of other specifications to normalize the files which will be massaged to conform:
0 string %%Prolog Prolog Predicate File (Non-Specific)
0 string %%gprolog Prolog Predicate File (GNU Prolog)
0 string %%swipl Prolog Predicate File (SWI-Prolog)
0 string %%yap Prolog Predicate File (YAP Prolog)
0 string %%eclipse Prolog Predicate File (ECLiPSe)
0 string %%bprolog Prolog Predicate File (B-Prolog)
0 string %%poplog Prolog Predicate File (Poplog)
0 string %%lpaprolog Prolog Predicate File (LPA Prolog)
0 string %%isoprolog Prolog Predicate File (ISO-Compliant Prolog)
I have created this last definition so that I may specifically tag those predicate files which I have confirmed as compliant with ISO Prolog specifications.
I do NOT want to use the "shebang" (i.e. #!/bin/gprolog) notation for first line auto-detection for execution.
[Additional] I just discovered a gotcha. How can I configure the installation to ensure any standard/builtin "shebang" notation is evaluated before my customized /etc/magic entries, but at the same time have my /etc/magic definitions be evaluated before any other magic sequences?
Guidance on search depth specification would be greatly appreciated.
