SUSORT - sort on any segy header keywords

susort <stdin >stdout [[+-]key1 [+-]key2 ...]

Susort supports any number of (secondary) keys with either
ascending (+, the default) or descending (-) directions for
each. The default sort key is cdp.

Note: Only the following types of input/output are supported
Disk input --> any output
Pipe input --> Disk output

Note: If the the CWP_TMPDIR environment variable is set use
its value for the path; else use tmpfile()

Example:
To sort traces by cdp gather and within each gather
by offset with both sorts in ascending order:

susort <INDATA >OUTDATA cdp offset

Caveat: In the case of Pipe input a temporary file is made
to hold the ENTIRE data set. This temporary is
either an actual disk file (usually in /tmp) or in some
implementations, a memory buffer. It is left to the
user to be SENSIBLE about how big a file to pipe into
susort relative to the user's computer.


Credits:
SEP: Einar, Stew
CWP: Shuki, Jack

Caveats:
Since the algorithm depends on sign reversal of the key value
to obtain a descending sort, the most significant figure may
be lost for unsigned data types. The old SEP support for tape
input was removed in version 1.16---version 1.15 is in the
Portability directory for those who may want to input SU data
stored on tape.

Trace header fields modified: tracl, tracr