Dennis Williamson

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Profile: I'm a Unix/Linux sysadmin

	2,618 reputation	bio	website	blog.denniswilliamson.us	visits	member for	2 years, 9 months
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Mar 4	comment	determining path to sourced shell script @clacke: I find that in all the versions of Bash that I tested from 2.05b to 4.2.37, including 4.1.9, that `.` and `source` worked identically in this regard. Note that `$_` must be accessed in the first statement in the file, otherwise it will contain the last argument of the previous command. I like to include the shebang for my own reference so I know what shell it's supposed to be for and for the editor so it uses syntax highlighting.
Feb 5	comment	How can I scroll within the output of my watch command? @xav0989: You would need to wrap your chain in curly braces or it will only `tail` the last command: `{ command1 && command2 && command3; } \| tail` - don't forget the spaces (after the opening and before closing brace) and semicolon after the last command. Remember, the whole chain will be executed each time `watch` reruns it.
Jan 23	comment	Is there a way to run 'screen' in read-only mode? @StephaneChazelas: I don't see any indication in the question that the OP is concerned about writability in other instances of a multiply-attached session. Besides, the `aclcng` command can specify particular users, particular commands and/or particular windows so that's fairly fine granularity. So that's not "everywhere".
Jul 20	comment	Why does this compound command report errors when copying directories? By "redirected" I assume you mean aliased. The `-i` option shouldn't cause the problem you're seeing. Is dir2 a symlink? That shouldn't matter, though.
Jul 20	comment	Why does this compound command report errors when copying directories? Do you get an error without `-a`? What happens if you use `-d` instead? Is dir2 a symlink?
Jul 20	comment	Why does this compound command report errors when copying directories? There's nothing wrong with the command line you posted. Check to see if either command is aliased or redefined as a function: `type -a rm cp`.
Jul 1	comment	Storing output of command in shell variable I forgot to say @Patrick in that last comment.
Jun 28	comment	What does dash “-” at the end of a command mean? "redundant and slightly weird" - Sometimes being explicit aids in clarity.
Jun 28	comment	Storing output of command in shell variable Piping `sleep` to `cat` is nonsensical, but perhaps useful for some types of testing. If pipes and redirection were the same, then piping into `while` wouldn't set up a subshell. Also, process substitution uses named pipes or `/dev/fd`. So, now try your tests, but add `& echo $!` at the end and do `ls -l /proc/PID/fd` in another teminal, substituting the PID that was echoed. Seriously, just try it.
Jun 28	comment	Storing output of command in shell variable @Patrick: No, they don't. They do have similarities, but they're different.
Jun 28	comment	Storing output of command in shell variable @Patrick: That's not a pipe, it's redirection. It's process substitution redirected into `done`.
Jun 4	comment	In linux, would it be possible to run a script every day 3 minutes later than the previous day? Here's a script I wrote to reschedule `at` jobs. It's not pertinent to the question, but it's tangentially related.
Jun 4	comment	In linux, would it be possible to run a script every day 3 minutes later than the previous day? @KeithThompson: But then you have to keep a counter and increment it.
Jun 4	comment	In linux, would it be possible to run a script every day 3 minutes later than the previous day? @Elmer: Oops! You are correct (except that you can't do running addition). I'll edit my answer.
May 31	comment	bash using a file name as input `echo "opening '$first_u_file'"` - you don't need to escape the single quotes and the variable gets properly quoted.
Mar 28	comment	Accessing bash [internal] brace expansion iteration number/variable Bash has some special variables/parameters, but nothing like Perl's `$_`. As I said before, "What are you really trying to accomplish?" See the `echo` example in l0b0's answer. There's no internal or implied variable. The expansion gets expanded all at once. The iteration is performed over the completed expansion by a `for` statement using a variable you supply. Bash has no concept of iterators in the sense that Python or Perl have.
Mar 28	comment	Accessing bash [internal] brace expansion iteration number/variable And, ultimately, the question is "Why?". What are you really trying to accomplish?
Mar 28	comment	Accessing bash [internal] brace expansion iteration number/variable "As you can see, bash is setting the iteration to $a" - because you're using a `for` loop.
Mar 28	comment	Accessing bash [internal] brace expansion iteration number/variable The output you're showing is not the actual output. It's more like `mv 1.something.1 1.something.2 1.something.3 1.something.4 1.something.5 2.something.1 2.something.2 2.something.3 2.something.4 2.something.5 3.something.1 3.something.2 3.something.3 3.something.4 3.something.5 4.something.1 4.something.2 4.something.3 4.something.4 4.something.5 5.something.1 5.something.2 5.something.3 5.something.4 5.something.5 ..something`. In other words the brace expansion is expanded completely and not iterated over. You must use a `for` loop for iteration.
Jan 22	comment	How do I redefine a bash function in terms of old definition? Instead of `eval`, you can use indirection: `local VAL=$(echo ${!1})`