What does ‘touch’ stand for

I'd gander a guess that it's there for FAT, File Allocation Table. But if you look at Wikipedia the "f" stands for "fixed" as in "fixed disks".

excerpt - http://en.wikipedia.org/wiki/Fdisk

For computer file systems, fdisk (for "fixed disk") is a command-line utility that provides disk partitioning functions. In versions of the Windows NT operating system line from Windows 2000 onwards, fdisk is replaced by more advanced tool called diskpart. Similar utilities exist for Unix-like systems.

Window's fdisk?

Granted the above has more to do with the Windows/DOS variant but the term "fixed disk" makes a lot of sense, since hard drives were often termed "fixed" in the olden days.

"fixed disk" definition

The definition of "fixed disk" also says the same.

excerpt - http://www.thefreedictionary.com/fixed+disk

Noun 1. fixed disk - a rigid magnetic disk mounted permanently in a drive unit

Other sources saying the same thing:

• http://www.computerhope.com/jargon/f/fixeddis.htm
• http://www.wisegeek.org/what-is-a-fixed-disk.htm#slideshow
• http://en.wikipedia.org/wiki/Hard_disk_drive

Original origins of "fixed disk"

Wikipedia's page on Hard Disk Drives also had this nugget:

excerpt

In 1961 IBM introduced the model 1311 disk drive, which was about the size of a washing machine and stored two million characters on a removable disk pack. Users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Non-removable HDDs were called fixed disk drives.

touch creates a new, empty file if the file doesn't exist because that's what it was designed to do. The utility has to contain code to handle that case specifically. The utility appeared in Unix V7; its manual described it thus:

touch — update date last modified of a file

touch attempts to set the modified date of each file. This is done by reading a character from the file and writing it back. If a **file* does not exist, an attempt will be made to create it unless the -c option is specified.

(I don't know what touch did if the file was empty. The underlying system call came later.)

I don't know for sure why touch was designed to make the file exist, but I suspect it's because of make. Why would you want to set a file's modification time to the current time? There are cases where it could be useful to set the modification time to a particular time, but that ability came later, the original touch could only set the modification time to the current time. A reason to do that is to re-run a make rule that depends on the file.

That is, suppose you have a file foo, and a makefile that declares a command to generate bar from foo. When you type make bar, the command is executed and bar is created. If bar exists and is newer than foo, make bar does nothing, because make assumes that bar has already been generated. However, if bar is older than foo, make thinks that bar is not up-to-date and needs to be regenerated.

But what if the rules to generate bar have changed? Then you have two options:

• rm bar; make bar
• touch foo; make bar

You would need foo to exist in order to generate bar, otherwise the command would typically not work.

The “touch” terminology was also present in the make utility: make -t bar would only pretend to run the commands, that is, it would set the modification time of bar to the current time without actually running the command to generate bar (you would do this if you thought that the changes to foo shouldn't affect bar). The touch utility was therefore a standalone version of the make -t feature.