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Top Forums Shell Programming and Scripting Understanding ampersand (&) usage in the command Post 302422338 by zaxxon on Tuesday 18th of May 2010 06:33:10 AM
Old 05-18-2010
You are right but I guess that this is just a typo and missing a 2nd adjacent & like marked bold here:
Code:
who && echo "Total number of users are `who|wc -l`"

This works then like if the 1st who is successful, the command following will be executed, maybe to check if "who" itself is available and working. Sending "who" in the background and then following up the rest of commands would make no sense.
 

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keyhead(1)						      General Commands Manual							keyhead(1)

Name
       keyhead - Change FITS or IRAF header keyword names

Synopsis
       keyhead [-hknv] <FITS or IRAF file> kw1=kw1a kw2=kwd2a ... kwn=kwdna

Description
       Change the names of keywords in FITS or IRAF image headers.  Each current image keyword whose entry is to be modified should be followed by
       an equal sign and a second keyword, with no intervening spaces.	If the -r option is used, the value of the second keyword is transfered to
       that  of the first. Otherwise, the name of the first keyword is changed to the second keyword.  To change keywords in a list of files, sub-
       stitute @<listfile> for the file names on the command line.  To change a lot of keywords, put them, one pair separated by an = sign with no
       spaces  per  line, in a file and substitute @<keylistfile> on the command line.	If two @ commands are present, the program will figure out
       which contains file names and which contains keywords.  Lines in a keyword list file which do not contain an = are ignored.

Options
       -h     Write HISTORY line into output header with sethead version, current date and time, and names of keywords set.

       -k     Write KEYHEAD keyword into output header with the keyhead version, current date and time, and names  of  keywords  whose	names  are
	      changed.	If a KEYHEAD keyword already exists, move the old value to a HISTORY line before writing the new value

       -n     Write a new file with an added "e" before the extension.

       -r letter
	      Replace  value of 1st keyword with value of 2nd keyword instead of changing the name of the 1st keyword to the 2nd keyword.  The 2nd
	      keyword remains in the header.  If the 1st keyword does not exist in the header, it is created.

       -v     Print confirmations of each keyword change.

Web Page
       http://tdc-www.harvard.edu/software/wcstools/keyhead.html

Author
       Doug Mink, SAO (dmink@cfa.harvard.edu)

6 July 2001							     WCSTools								keyhead(1)
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