What does the character , mean in bash?

Question

What does , mean in bash? For example what would the , in "accurev update -9 2>,update 1>&2" mean? (accurev is a version control software)

Sorry for the lame question, I just dunno how to google for special characters.

Answer 1

It has no special meaning. The command redirects to a file called ,update.

Answer 2

A comma can be used in brace expansion, but there are no braces in the example you show.

This command would store its output in two files, one called "def" and the other called "abcdef":

echo hello | tee {,abc}def

or this one in "file1" and "file2":

echo hello | tee file{1,2}

Commas can be used to separate commands in an arithmetic operation in a let statement or the equivalent (()) construction:

let a=1,b=2    # no spaces permitted
(( a = 1 , b = 2 ))
(( ++c, --d, e+=4 ))

You can use commas in a for statement to work with additional variables besides the primary index rather than putting the variable manipulation in the body of the for. It's probably bad programming practice to do this:

for ((i=1,j=4; i<4,j<7; i++,j+=2)); do echo $i $j; done

Commas can also be used in Bash 4 to change a string to lowercase (only a couple of variations are shown):

$ words="This is a TEST"
$ echo ${words,,}  # the whole string is lowercased
this is a test
$ echo ${words,}   # only the first character
this is a TEST

Answer 3

Dennis is right in general, but your specific example runs accurev update -9, and puts the stderr output into a file called ,update (with , as part of the filename), then puts stdout to the same place that stderr goes to (the file named ,update in this case).

Answer 4

there is a comma operator in bash that will run two commands but I don't believe it is used by your example check out the advanced bash scripting guide http://tldp.org/LDP/abs/html/ops.html

an example:

for ((a=1, b=1; a <= LIMIT ; a++, b++))
do  # The comma chains together operations.
  echo -n "$a-$b "
done