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Mark G. Sobell

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Mark G. Sobell, author of many best-selling books, including A Practical Guide to Fedora and Red Hat Enterprise Linux, Sixth Edition, A Practical Guide to Ubuntu Linux, Third EditionA Practical Guide to Linux Commands, Editors, and Shell Programming, Third Edition (all from Prentice Hall), has more than thirty years of experience working with UNIX and Linux. He is the president of Sobell Associates Inc., a consulting firm that designs and builds custom software applications for UNIX and Linux systems and provides training and support.

Mr. Sobell started working with computers part time after high-school where he worked on the Dartmouth Time-sharing system where they developed the BASIC programming language and on IBM OS/360 systems. He start ...more

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Mark G. Sobell's Blog

Mark G. Sobell isn't a Goodreads Author (yet), but they do have a blog, so here are some recent posts imported from their feed.

Use := to Assign a Default Value to an Unset Variable

You can change the value of a null or unset variable to its default in a script using the := modifier:

${name:=default}

When the shell expands the expression ${name:=default}, it sets the value of name to the expanded value of default. If a script contains a line such as the following and LIT is unset or null at the time this line is executed, the shell assigns LIT the value /home/max/literature:

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Published on May 03, 2012 15:20

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Mark G. Sobell’s books

Average rating: 3.95 · 586 ratings · 44 reviews · 36 distinct works • Similar authors

	A Practical Guide to Linux Commands, Editors, and Shell Programming 4.02 avg rating — 330 ratings — published 2005 — 21 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to Ubuntu Linux 3.88 avg rating — 90 ratings — published 2007 — 14 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to Fedora and Red Hat Enterprise Linux 3.78 avg rating — 87 ratings — 22 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to Linux really liked it 4.00 avg rating — 33 ratings — published 1997 — 6 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to Red Hat Linux: Fedora Core and Red Hat Enterprise Linux 3.92 avg rating — 26 ratings — published 2004 — 4 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to the UNIX System (3rd Edition) 3.89 avg rating — 19 ratings — published 1984 — 4 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to Solaris 3.67 avg rating — 18 ratings — published 1999 — 3 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	UNIX System V: A Practical Guide (3rd Edition) 3.71 avg rating — 17 ratings — 5 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	Hands-On Unix: A Practical Guide With the Essentials of Coherent 3.50 avg rating — 4 ratings — published 1994 — 4 editions	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars
	A Practical Guide to Red Hat Linux 8 0.00 avg rating — 0 ratings	Error rating book. Refresh and try again. Rate this book Clear rating 1 of 5 stars 2 of 5 stars 3 of 5 stars 4 of 5 stars 5 of 5 stars