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BSD 4.3tahoe

.TI F77/ERROR "Sep. 15, 1984"
Using the 'error' Command for Syntax Errors

This help file describes the use of the UNIX 'error' command with
syntax error messages;  for execution errors, see "help f77 error_msgs"
and for debugging, see "help f77 debugging".

Normally, f77 writes syntax error messages on the screen, you
copy them down and then edit the source file(s) and correct the
errors.  If you use the 'error' command, instead of having the error
messages displayed on the screen, they are inserted by the appropriate
lines in the source file.

As an example, suppose prog.f contains:

.nf
		print, " hi "
		sqr2p = sqrt(2.0)
		sqr2e = 2.0^0.5
		print *, "square root of 2.0 is", sqr2p, sqr2e
		end
.fi

Compiling prog.f generates these messages:

.nf
	% f77 prog.f
	prog.f:
	   MAIN:
	Error on line 1 of prog.f: syntax error
	Error on line 3 of prog.f: syntax error
	
	Error.  No assembly.
	% 
.fi

These can be piped to the error utility (piping both standard output
and standard error):

.nf
	% f77 prog.f |& error
	
	1 file contains errors "prog.f" (2)
	
	File "prog.f" has 2 errors.
		2 of these errors can be inserted into the file.
	You touched file(s): "prog.f"
.fi

The output to your terminal notes that two error messages have been
inserted into the file prog.f.  Prog.f now contains:

.nf
	C###1 [f77] Error on line 1 of prog.f syntax error%%%
		print, " hi "
		sqr2p = sqrt(2.0)
	C###3 [f77] Error on line 3 of prog.f syntax error%%%
		sqr2e = 2.0^0.5
		print *, "square root of 2.0 is", sqr2p, sqr2e
		end
.fi

Each of the syntax errors has been inserted in the file in front of
the line causing the error.  They are inserted as Fortran comments,
so they will not cause new syntax errors if you forget to remove them.

You can use the editor and look for `###' in the error messages,
and then fix the errors.  If the ``-v'' flag is used:

	% f77 prog.f |& error -v

error will finish by invoking the visual editor, vi, with
the first source file containing errors.

It is easier to see what error does by using it than to understand
it by looking at examples.  Error is particularly useful when
there are few errors in a large source program.
If there are too many errors, such as if a dimension statement is missing,
the inserted errors can be overwhelming; however:

	:g /###/d

will eliminate them (along with any other lines containing ``###'').

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