small programs used on the command line to do a specific job
30
votes
2answers
6k views
What does “--” (double-dash) mean?
I have seen -- used in the compgen command.
For example:
compgen -W "foo bar baz" -- b
What is the meaning of the --.
21
votes
6answers
2k views
Linux tools to treat files as sets and perform set operations on them
Does anyone know of any linux tool specifically designed to treat files as sets and perform set operations on them? Like difference, intersection, etc?
85
votes
16answers
38k views
Repeat a Unix command every x seconds forever
There's a builtin Unix command repeat whose first argument is the number of times to repeat a command, where the command (with any arguments) is specified by the remaining arguments to repeat. For ...
21
votes
5answers
2k views
Is there any option with 'ls' command that I see only the directories?
Sometimes, I need to check only the directories not files. Is there any option with the command ls? Or is there any utility for doing that?
EDIT: I'm using Mac OS X, and ls -d gives me . even though ...
13
votes
9answers
6k views
Tool in UNIX to subtract dates
Is there any tool in Solaris UNIX (so no GNU tool available) to subtract dates? I know that in Linux we have gawk that can subtract one date from another. But in Solaris the maximum we have is nawk ...
3
votes
4answers
8k views
How to recover data from a bad SD card?
I have a 4GB SD card with some family pictures on it that I need to recover. When I insert the card into my card reader, it shows up as an unknown 32MB device (as /dev/sde) and cannot be mounted. When ...
11
votes
2answers
215 views
`test` and `[` - different binaries, any difference?
I noticed while answering another question that test and [ are different binaries, but the [ manpage pulls up test's. Besides the requirement for an ending ], is there any difference? If not, why are ...
5
votes
4answers
567 views
A standard tool to convert a byte-count into human KiB MiB etc; like du, ls1
Is there a standard tool which converts an integer count of Bytes into a human-readable count of the largest possible unit-size, while keeping the numeric value between 1.00 and 1023.99 ?
I have my ...
26
votes
4answers
2k views
What is the difference between a builtin command and one that is not?
Is there any intrinsic difference between a builtin command and another command which can nominally do the same thing?
eg. Do builtins get "special" treatement? ... is there less overhead running ...
12
votes
3answers
1k views
Why use superflous dash (-) to pass option flags to tar?
To create a tar file for a directory, the tar command with compress, verbose and file options can be typed thus:
$ tar -cvf my.tar my_directory/
But it also works to do it this way:
$ tar cvf ...
10
votes
1answer
329 views
What do all the pictures on the front of the “Unix and Linux System Administration Handbook” represent?
I'm a newcomer to Unix and Linux, and I've been trying to get up to speed on everything. One of the guides I've used is the "Unix and Linux System Administration Handbook"
It's a pretty great book, ...
6
votes
1answer
246 views
Is there a way to make perl -i not clobber symlinks?
A friend of mine points out that if you do:
perl -pi.bak -e 's/foo/bar/' somefile
when "somefile" is actually a symlink, perl does just what the docs say it will do:
It does this by renaming ...
4
votes
2answers
835 views
Combine input from multiple files/pipes without clobbering lines or blocking?
Is there a tool that will take input from multiple files or pipes and write it to stdout, without blocking on reads, such that individual input lines come out intact? I basically want to multiplex a ...
18
votes
4answers
599 views
Are Linux utilities smart when running piped commands?
I was just running a few commands in a terminal and I started wondering, does Unix/Linux take shortcuts when running piped commands?
For example, let's say I have a file with one million lines, the ...
9
votes
3answers
404 views
Doing two things with output from a command
I have a program texcount that outputs the number of words in my LaTeX document. I can also pipe the output of this to sed to make the newlines TeX linebreaks and write this to a file which I can then ...
11
votes
4answers
2k views
Usage of dash (-) in place of a filename
For a command, if using - as an argument in place of a file name will mean STDIN or STDOUT.
But in this example, it creates a file with the name -:
echo hello > -
How can I make - in this ...
1
vote
3answers
115 views
How to check which process is using a given file descriptor?
Somewhere in the middle of my application, the framework I'm using (ROOT) gives me the following error:
*** Break *** write on a pipe with no one to read it
SysError in ...
