Questions tagged [unix-shell]
131 questions
44
votes
5 answers
Faking the date for a specific shell session
I'm certainly trying to achieve something weird here, but I want to fake the date locally for a shell session on GNU/Linux.
I need to black-box test how a program behaves at different dates, and modifying the system-wide date can have unwanted side…
nicoulaj
- 1,245
43
votes
6 answers
compressing dd backup on the fly
Maybe this will sound like dumb question but the way i'm trying to do it doesn't work.
I'm on livecd, drive is unmounted, etc.
When i do backup this way
sudo dd if=/dev/sda2 of=/media/disk/sda2-backup-10august09.ext3 bs=64k
...normally it would…
Phil
- 2,119
34
votes
4 answers
Append an echo to file?
In linux, how do I do something like
echo 'hello world' > log.txt
but instead of overwriting the contents of log.txt, it appends to the end of of log.txt?
learningtech
- 7,769
31
votes
2 answers
When to use single quotes, double quotes, or no quotes in grep?
While trying to search for a simple pattern "hello" in a file, all the following forms of grep work:
grep hello file1
grep 'hello' file1
grep "hello" file1
Is there a specific case where one of the above forms work but others do not.
Does it make…
TheLameProgrammer
20
votes
8 answers
portable unix way to join strings with separator
Is there a portable unix shellscripting way of joining a number of strings together with a given separator, like so:
$ strjoin --- foo bar baz quux
foo---bar---baz---quux
Sure I could use a $scripting_language one liner or an ugly explicit loop in…
JanKanis
- 603
16
votes
7 answers
In *nix, how to determine which filesystem a particular file is on?
In a generic, modern unix environment (say, GNU/Linux, GNU/Solaris, or Mac OS X), is there a good way to determine which mountpoint and filesystem-type a particular absolute file path is on?
I suppose I could execute the mount command and manually…
smokris
- 715
14
votes
2 answers
cp -p will preserve times for some files but not all?
I have a source directory on a machine with a bunch of files, all with the same permissions, that I want to copy to another directory, that is mounted via SMB.
[tmark@dexter JR09141045 roche_454_transfer]$ ls -l /source_dir
total 71348
-rwxrwxrwx 1…
tmark
- 141
14
votes
5 answers
Copy file permissions, but not files in Unix
(From : https://stackoverflow.com/questions/15245144/copy-file-permissions-but-not-files, closed because off-topic)
I have two copies of the same directory tree. They almost have the same files in both (one version may have a couple extra or missing…
Mariano Paniga
- 261
14
votes
8 answers
Deleting a UNIX directory with a hyphen in the name
Through a boneheaded maneuver on my part, I accidentally created a directory called (for instance) -A, and ended up filling it with files.
I want to delete said directory. I've tried:
rmdir -- -A
but it then tells me that the directory still has…
Kate Bertelsen
- 243
13
votes
6 answers
How do i find out which Fedora version I'm running from the cli (not uname -a)?
I want to know if the box is Fedora Core 4 or Redhat 9, or CentOS, etc... not if it has Kernel 2.6.x
Zak
- 1,042
12
votes
9 answers
'Argument list too long' error while copying a large number of files
I am using the following command:
\cp -uf /home/ftpuser1/public_html/ftparea/*.jpg /home/ftpuser2/public_html/ftparea/
And I am getting the error:
-bash: /bin/cp: Argument list too long
I have also tried:
ls…
icelizard
- 732
10
votes
1 answer
Using a shell script to check if rsync made any changes
I've got a bash script that rsync's two directories. Sometimes there's a change, odds are there's nothing.
I want to run a command only if rsync actually made a change (add/update a file). Otherwise I want to just skip it. Is there a return…
raccettura
- 141
7
votes
2 answers
When do file extensions override shebang lines on Linux?
Some PHP cron jobs started failing on a shared server recently. They had been working without error and no updates for nearly a year, but now would no longer run due to syntax errors. What was going on?
It turns out these scripts were suddenly now…
drench
- 205
6
votes
2 answers
How do I prevent bash $ substitution?
I'm trying to preserve $if below and
would like the following to output
$if
bash is getting in the way by doing
$ substitution
$ sed -e 's:\\$:\\$:g' < $if
> ENDOFFILE
or
$ tr '$' '\$' < $if
> ENDOFFILE …
user27164
5
votes
2 answers
Kill all currently running cron jobs
For some reason my cron job scripts aren't exiting cleanly and they're backing up my server. There are currently a couple hundred processes running for one of my users. I can use the following command to kill all processes by that user, but how can…
