Once invoked, edhead responds to a number of commands. These include help, which gives a summary of the commands and their formats; exit, which causes program termination; NNN (a non-negative decimal integer), when alone causes edhead to retreive the header for that data bin and display it. NNN (a bin number) followed by a header keyword and one or more arguments requests that the specified header variable(s) be set to the new values supplied. edhead maintains a notion of the current bin, which is the last bin accessed, in a manner similar to line-oriented text editors. Hence, it is not necessary to precede header keywords with the bin number if the alteration is to be made on the current bin. In addition, one can type * in place of NNN if one wishes to alter all the bins in the data file. In the description which follows, [NNN] refers to an explicitly typed bin number (witout the square brackets), an *, or possibly nothing if the appropriate bin number is the current bin. Headers can only be altered if the -w flag was included in the invocation and the file is a disk file. The header keywords are exactly those printed out when a header is displayed on the screen.
There are four classes of header variables: those containing single integer values, those containing an array of integer values, those containing a single descriptor string, and those which contain an array of descriptor strings.
Header variables which are single integers include: event, epoch, chans, sums, tpfuncs, pp10uv, verpos, odelay, totevnt, clktick, timehi, timelo, condcode, presampling, trfuncs, totrawrecs, totrejects, binnumber, and cprecis. The command format for these is:
Currently the only header variable which consists of an array of integers is rejcounts. To change one element of this array, enter:
Four header variables consist of strings of up to 39 characters. These are : expdesc, subdesc, condesc, and bindesc. These can the replaced with two consecutive lines beginning with:
The final class of header variables is the arrays of descriptors. One element in one of these arrays can be altered by employing a command of the form:
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