The shell is unix's command-line interface. You can type commands in a shell interactively, or write scripts to automate tasks. Use this tag for questions applying to /bin/sh and most compatible shells (ash, bash, ksh, zsh, …).

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2
votes
1answer
347 views

awk function with a number parameter for the column you want to print

I want to use my awk shortcut as a function, so that I can pass the column number which then prints me the output. My aliases are: alias A="| awk '{print \$1}' alias G="| grep -i' Instad of typing: ...
4
votes
1answer
656 views

What's the conf file reading between login and non-login shell?

I found that those are .bash_profile, .bashrc, .bash_login, .profile. What's the reading sequence between them?
2
votes
2answers
968 views

Timeout doesn't occur when reading from fifo using `read`

Look at this code: while read -t 3 line; do echo ${line} done < /opt/data.log data.log is a fifo. One process is writing to this, and this code should be reading it to show to the user. But ...
4
votes
3answers
3k views

Sending the output from 'dd' to awk/sed/grep

I'm trying to approximate the computer's write speed using dd: dd if=/dev/urandom of=/dev/null bs=1K count=10000 which gives the following output 10000+0 records in 10000+0 records out 10240000 ...
2
votes
2answers
1k views

How to convert a group of video files using FFMPEG?

I have several video files in a directory and I want to convert all of them into other video formats. Is there any way that I can convert all of them in just one go using FFMPEG. I mean without having ...
1
vote
2answers
201 views

How do I specify which version of a program to run?

Here's my situation: I have two versions of postgres installed, and with the two versions, come two different psql interactive terminals. One is located at /usr/bin/psql, and starts when I run # ...
0
votes
2answers
213 views

Why does this compound command report errors when copying directories?

if one executes the following two commands in one line, as follows, rm -rf dir ; cp -r dir2 dir it may complain that cp can not create directory dir/subdir: File exists but if these two commands ...
18
votes
6answers
12k views

How can I set my default shell to start up tmux

I would like my default bash shell to go straight into tmux instead of my always having to type tmux every time.
3
votes
6answers
6k views

Difference between “echo $SHELL” and “which bash”

I am trying to determine the location of bash interpreter on my Solaris system and I am a bit confused. When I type: echo $SHELL The resulting path is: /bin/bash And when I type: which bash I ...
16
votes
1answer
7k views

what do you mean by interactive shell?

UNIX: The Complete Reference, Second Edition by Kenneth H. Rosen et al. You can start another shell after you log in by using the name of the shell as a command; for example, to start the ...
2
votes
1answer
930 views

Time validation with regex

I'd like to make validation about time stamp of one of my log file. But it seems I have problem on my expression in case statement. TIME value might be something like 11:49 or 2011. And I just want ...
2
votes
1answer
157 views

How do I create history files with date automatically attached?

E.g. at the end of the session for each day I want to create a history file with the date attached at the end. So, say, history > history07162012.txt or something like that.
18
votes
1answer
956 views

Is there a standard command that always exits with a failure?

I want to test my script with a command that fails. I could use an existing command with bad arguments. I could also write a simple script that immediately exits with a failure. Both of these are easy ...
2
votes
2answers
485 views

How to copy/move/delete files from the shell?

It's surely easy to do while using a graphical environment, but when I'm using the shell I have no idea on how to do that, I already tried to use copy, move, delete, and I discovered that these word ...
13
votes
3answers
5k views

How to set window size and location of an application on screen via command line?

I want Firefox window to be opened in a specific size, and location on screen using a shell command, for example: firefox myfile.html size 800x600 location bottom-left Is there such a command?
1
vote
1answer
783 views

Shell script running two Perl scripts based on input

I am new to shell script. I have two Perl scripts for text processing based on two different input files. I would like to have one shell script that runs based on conditions. If (input file) matches ...
2
votes
2answers
468 views

How come lvextend allocates less than the specified amount of space?

I am trying to extend a volume, let's call it /dev/vol1. I see the initial volume size is 500MB when I call: df --block-size=M /dev/vol1 then to extend it 100MB more I call: lvextend -L+100M ...
23
votes
6answers
4k views

Using VI keys to edit shell commands in UNIX

I used to have a co-worker who was really good at UNIX. He showed me how to use Vi key bindings to edit my shell commands. He placed the command in a file that ran every time I logged in. Since ...
6
votes
3answers
701 views

Get a list of 3 letter commands on Mac OS X

How can I either create or find a list of 3-letter unix commands on Mac OS X? I'd like to create a new program/command for a project. I'd like to make it a 3-letter name, but I don't want to conflict ...
2
votes
2answers
392 views

Bash Process Substitution does not work as 'root' on OS X

OS X 10.6.8, if I use Bash Process Substitution as 'root', it just doesn't work. Is it supposed to be so? Why? Note: here's what I mean... "<(list)" mysql -D robottinosino < <(echo ...
2
votes
1answer
508 views

remote execution via ssh doesn't follow links?

ssh server ls /var/lib/edumate/backup/weekly/*DBB* returns one file /var/lib/edumate/backup/weekly/DBB.0.db2inst1.NODE0000.CATN0000.20120610020013.001 but ssh server ls /data/backup/weekly/*DBB* ...
0
votes
1answer
757 views

Create a fake shell in Linux?

I am not talking about shell programming or making a whole new shell like Bourne or Korn Shell.... I just want a user accessing ftp through port 21 to be directed to this shell which can support some ...
7
votes
4answers
923 views

Iterate over n files?

I've got something fairly simple I want to do. I want to use montage on a directory that contains thousands of images, with very few options, namely: me@home$ montage -size 256x256 DSC01*.JPG.svg ...
18
votes
2answers
7k views

Are there naming conventions for variables in shell scripts?

Most languages have naming conventions for variables, the most common style I see in shell scripts is MY_VARIABLE=foo. Is this the convention or is it only for global variables? What about variables ...
11
votes
2answers
1k views

Can git configuration be set across multiple repositories?

Git seems to support configuration values at three levels: Per-system global settings (stored in /etc/git-core) Per-user global settings (stored in ~/.gitconfig) Per-repository local settings ...
20
votes
5answers
7k views

Make `rm` move to trash

Is there a Linux script / application which, instead of deleting files, moves them to a special “trash” location? I’d like this as a replacement for rm (maybe even aliasing the latter; there are pros ...
7
votes
1answer
3k views

Korn Shell: End, pgup, pgdown, and delete key not working

So basically my End, Pageup/Pagedown, and Delete key are not working in ksh93. I'm running FreeBSD by the way. My arrow keys are working, and so is my home key. Those keys work when I put this in my ...
30
votes
2answers
13k views

What does “3>&1 1>&2 2>&3” do in a script?

I saw this line in a script: DEVICE=`dialog --inputbox "Festplatten-Laufzeit auslesen. Gebe Sie das gewünschte Device an: " 0 70 "" 3>&1 1>&2 2>&3` What is 3>&1 ...
-1
votes
3answers
324 views

Duplicate bash prompts

I'm having an interesting issue with XFCE Terminal/Gnome Terminal (not reproducible in XTerm), where executing bash or logging in using login or su will open a new Bash instance inside a Bash instance ...
1
vote
3answers
11k views

How to change the working directory for a shell script

I have a Python script that looks files up in a relative directory. For example: the Python script is in /home/username/projectname/. I have a file that is being called within the Python script that ...
3
votes
4answers
640 views

Prevent a command from being executed after another command

I would like the shell to warn me for potential errors I'm about to make. How can I prevent a command cmd2 from being executed after cmd1. For example: $ tar tf file.tar $ rm !$ Here, I just ...
6
votes
3answers
14k views

Automating textual input from a bash script without using EOF

I'm running Ubuntu Linux. Suppose there is a program called myprogram. This program prompts the user for input; specifically, the user must type an integer when prompted and press Enter. I would ...
17
votes
2answers
4k views

Does redirecting output to a file apply a lock on the file?

If I have a command $ ./script >> file.log that gets called twice, with the second call occurring before the first one ends, what happens? Does the first call get an exclusive lock on the ...
12
votes
1answer
956 views

Can I restrict a user to use special programs?

Is it possible to add a user and restrict him to run special programs? For example after this user logs in, he can only open Firefox to use Internet and no other programs can be run by this user. For ...
3
votes
2answers
917 views

Search for files with a specific size inside recursive zipped archives

I have a folder with several files. These files are either .xml or .zip files. These .zip files contain .xml and/or .zip files. These .zip contains also .xml or .zip, and so on... until we finally ...
3
votes
1answer
1k views

Evaluating the return value of a command line

How do I evaluate or calculate the return value of a command line? For exemple, I count the number of lines with a grep and I want to know if that value is above X. If so, I want to print the number ...
2
votes
4answers
722 views

Stripping all vowels but the first from a set of strings

I have a string comprised of multiple substrings, separated by underscores. For example: AbcdAEfd_hEgdgE_AbAAAAA. I need to remove all vowels except the first from each substring. So: AbcdAEfd -> ...
6
votes
1answer
2k views

A couple arithmetic related commands, Dash, POSIX shell, sh, Increment

When pre/post incrementing a variable, in POSIX Shell, what is the difference between these two examples. They seem like they would have the same consequences, but would they be used differently? ...
3
votes
1answer
4k views

Shell script hangs on mail command

I'm finding that a call to the mail command is causing a script to suspend without error. To close the script I have to ctrl-c or issue a kill command on the process id. The pertinent section of ...
4
votes
1answer
7k views

shell backup script, missing `]`

I'm putting together a simple backup script that will tar contents of a folder, then move that file to a backup server. The script makes sure that the tar file exists and is not zero bytes before ...
18
votes
6answers
823 views

How stable are Unix shell “stdin/stdout APIs”?

grepping, awking, sedding, and piping are day-to-day routine of a user of any Unix-like operating system, may it be on the command line or inside a shell script (collectively called filters from now ...
2
votes
1answer
159 views

Restoring an option at the end of a function in zsh

I'm writing a zsh shell function (as opposed to a script) where I would really like the extended_glob option to be enabled. But since the function runs in the caller's context, I don't want to clobber ...
8
votes
3answers
32k views

How can I delete all files with a particular extension in a particular folder?

If I set the current/working directory (navigating to it using cd) to some particular directory and then type: rm *.xvg What will this command do? Is it true that the above command will only delete ...
5
votes
1answer
835 views

How to define a `bc` function for later use?

I've always found bc kind of mysterious and intriguing. It was one of the original Unix programs. And it's a programming language unto itself. So I gladly take any chance I can find to use it. Since ...
5
votes
3answers
1k views

Auto-completion of words from the terminal buffer

In editors like vim and emacs, one can use hotkeys like C-p (vim) or M-/ (emacs) to perform auto-completion on the current word using other words in the same buffer. Is it possible to achieve the ...
31
votes
2answers
9k views

What does dash “-” at the end of a command mean?

Given the following command: gzip -dc /cdrom/cdrom0/file.tar.gz | tar xvf – What does the - at the end of the command mean? Is it some kind of placeholder?
6
votes
1answer
555 views

Ksh features incorporated into Zsh?

I have been a user of Bash for some time. I want to learn at least one other shell now, so I have been picking up the Korn Shell. However, it doesn't look like Ksh has had major updates for almost ...
4
votes
2answers
2k views

delete first line of file only if blank using sed

I have a solution for this in awk: awk '{if (NR==1 && NF==0) next};1' somefile but was unable to find one that worked in sed. E.g., sed -i.bak '/^$/{1,1d;}' somefile ended up deleting ...
22
votes
4answers
27k views

How to copy some, but not all files?

So, you can use the * as a wild card for all files when using cp within context of a directory. Is there a way to copy all files except x file?
1
vote
1answer
564 views

Detached screen on a remote host

I have a local script that runs a remote script via ssh. The local script is minecraft.php: ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -i {$this->pemkey} {$this->ssh_user} ...