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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7
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6answers
8k views

What's the best way to count the number of files in a directory? [duplicate]

If parsing the output of ls is dangerous because it can break on some funky characters (spaces, \n, ... ), what's the best way to know the number of files in a directory? I usualy rely on find to ...
6
votes
2answers
3k views

Manipulate file name piped from find command

I'm relatively new to Bash and am trying to do something that on the surface seemed pretty straightforward - run find over a directory hierarchy to get all of the *.wma files, pipe that output to a ...
5
votes
6answers
2k views

Portable way to find inode number

At first I used stat -c %i file (to help detect the presence of a jail), which seemed to work on any Linux distribution under the sun. On OS X' I had to use ls -i file | cut -d ' ' -f 1. Is there ...
22
votes
4answers
24k 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 ...
19
votes
5answers
5k views

How can I create an alias for a git [action] command (which includes spaces)?

Most of my my aliases are of this form: alias p='pwd' I want to alias git commit so that it does git commit -v But trying to create an alias with a space gives an error: $ alias 'git commit'='git ...
13
votes
3answers
21k views

Why I can't escape spaces on a bash script? [duplicate]

I'm trying to escape the space char for a path in Bash, but neither using a backslash or quotes works. .sh script: ROOT="/home/hogar/Documents/files/" FILE=${ROOT}"bdd.encrypted" ...
13
votes
2answers
10k views

/dev/tcp listen instead of nc listen

With a netcat listener like: nc -l <port> < ~/.bashrc I can grab my .bashrc on a new machine (doesn't have nc or LDAP) with: cat < /dev/tcp/<ip>/<port> > ~/.bashrc My ...
13
votes
1answer
5k 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 ...
12
votes
3answers
5k views

How to “send” variable to sub-shell?

I run the following script: VAR="Test" sh -c 'echo "Hello $VAR"' But I get : # ./test.sh Hello How can I "send" the variable VAR of my script to the shell created with sh -c?
10
votes
2answers
2k views

Closing a file descriptor, >&- vs <&-

In the bash tutorial I am reading, it says that if you open a file descriptor for reading, i.e. exec 3< echolist Then you must close it like this, exec 3<&- However, if you open a file ...
9
votes
1answer
257 views

Security Implications of using unsanitized data in Shell Arithmetic evaluation

In a comment to a recent question, Stéphane Chazelas mentions that there are security implications to double parentheses arithmetic such as: x=$((1-$x)) on most shells. My Google skills seem to be ...
9
votes
2answers
2k views

Use HERE file and redirect output of command

I have the following code in a batch script: mpirun -np 6 ./laplace <<END 100 100 100 0.01 100 3 2 1 END | tail -n 1 > output But it isn't working. What I want it to do is to use the HERE ...
8
votes
2answers
4k views

Can files be created with permissions set on the command line?

When creating directories, mkdir -m <mode> <dir> provides for creating one or more directories with the given mode/permissions set (atomically). Is there an equivalent for creating files, ...
8
votes
2answers
6k views

How to make exported shell variables permanent?

export LD_PRELOAD=/usr/lib/libtsocks.so It's ok that I can export in this way, but how can I make it permanent? I want LD_PRELOAD to still be changed after a reboot. I'm using Ubuntu and Fedora
7
votes
3answers
627 views

why for loop doesn't raise “argument too long” error?

I found that this would raise the "argument too long" error: ls *.* And this would not raise it: for file in *.* do echo $file done Why?
6
votes
3answers
476 views

Understanding environmental variables in different contexts

Trying to understand the behaviour of the environment in Linux (Ubuntu 13.04 concretely), I've find different situations where setting envirionment variables are used or defined for/in different ...
6
votes
2answers
2k views

How to trigger error using Trap command

I am using Ubuntu 12.04.2. I am trying to use "trap" command to capture abnormal or error in my shell script but I am also trying to manually trigger "Error" exit. I have tried exit 1, but it won't ...
5
votes
2answers
209 views

How can I force bash to deallocate a brace expanded variable without name?

For benchmarking, I ran the command: for i in {1..100000000}; do echo "$i" line >> file done Bash expanded the braces and stored the list 1 2 3 4 5 6 ... 100000000 in memory. I thought ...
5
votes
5answers
17k views

How to start a program in the background

The program Boblight does not run in background. There is no noticeable difference between executing sudo boblightd and sudo boblightd& How can I solve this problem that the console will ...
5
votes
4answers
2k views

Where do I change my shell?

If I wanted to use zsh, for instance, rather than bash, where would I make this change for the current user?
3
votes
7answers
740 views

Batch renaming of files [duplicate]

I have a directory full of images: DSCN4749.JPG DSCN4750.JPG DSCN4892.JPG ... And I would like a one-liner to rename them to (say). dscn4749.jpg dscn4750.jpg dscn4892.jpg ... How do I do this? ...
15
votes
4answers
4k views

Why do some commands 'hang' the terminal until they've finished?

Sometimes you run a program from the terminal, say, lxpanel†. The terminal won't drop you back to the prompt, it'll hang. You can press Ctrl+C to get back to the prompt, but that will kill ...
12
votes
3answers
13k views

Confusing use of && and || operators

I was skimming through an /etc/rc.d/init.d/sendmail file (I know this is hardly ever used, but I'm studying for an exam), and I've become a bit confused about the && and the || operators. ...
8
votes
5answers
1k views

Convert file contents to lower case

I have temp file with some lower-case and upper-case contents. Input Contents of my temp file: hi Jigar GANDHI jiga I want to convert all upper to lower. Command I tried the following command: ...
8
votes
1answer
7k views

How to hide commands typed in a Linux shell?

Is there a way to hide what I'm typing in a shell, so the terminal doesn't echo my keystrokes, while still keeping the output of the command? For example, if I run ip addr show, the only thing on the ...
8
votes
5answers
3k views

`highlight` command

Is there a command which can be used to easily highlight (with colors, bold text or inverted back-/foreground) specific strings in stdin while passing the entire string to stdout? I'm thinking of ...
7
votes
2answers
1k views

What is word splitting? Why is it important in shell programming?

I'm getting confused about the role word splitting plays in zsh. I have not been exposed to this concept when programming in C, Python or MATLAB, and this has triggered my interest of why word ...
6
votes
5answers
4k views

Convert linux sysuptime to well format date

I want to display /proc/uptime in well format as: DD:HH:MM:SS /proc/uptime give me up time of system in seconds, is there a standard solution that convert seconds to this format?
6
votes
1answer
6k views

Changing the default shell without chsh or administrator priviledges

I saw the following snippet in this thread: How to change from csh to bash as default shell sleep 2 if (-x /usr/local/bin/bash) then exec /bin/sh -c '. ~/.profile; exec /usr/local/bin/bash' endif ...
6
votes
4answers
16k views

Why is echo ignoring my quote characters?

The echo command isn't including the complete text that I give it. For example, if I do: $ echo ' echo PARAM=` grep $ARG /var/tmp/setfile | awk '{print $2}' ` ' It outputs: echo PARAM=` ...
6
votes
3answers
393 views

“mkdir foo; svn mv * foo”

I often want to do some variant of this idiom: $ mkdir 2010 $ svn mv * 2010 Of course, I get an error because the glob matches 2010 as well: svn: Cannot copy path '2010' into its own child ...
6
votes
1answer
343 views

Can I have my shell history record how wildcards expanded?

If I run: $ ls * foo bar buzz $ history | tail -1 ls * You can see that in my shell history it remembers that I ran ls * rather than ls foo bar buzz. Ideally, I'd like to record both in separate ...
5
votes
2answers
537 views

Why doesn't my loop over the output of ls work?

I am trying to feed Directory names into a for loop. My code is as follows: td='/Test/TopDir/' cd "$td" for x in $(ls -d */ | cut -f1 -d'/'); do echo x=$x done The top directory I run this on ...
5
votes
4answers
150 views

Is it shell portable to run a command on the same line after variable assignment?

Is there any standard that covers the portability of running a command after variable assignment on the same line? APPLE="cider" echo hi How portable is something like that? Where will it work and ...
5
votes
2answers
6k views

Trouble in script with spaces in filename

I've got a script that scp's a file from remote host back to local. Sometimes the file names contain spaces. scp does not like spaces in its file names. For some reason my attempts at handling the ...
5
votes
2answers
5k views

How to get a clean environment in a ksh shell?

I need to get rid of all the environment variables in a Ksh shell. I can fork a new instance, but it will inevitably source some init files (as far as I know .profile, .kshrc). Is there a way to ...
5
votes
1answer
1k views

How to pipe the result of 'date' command to 'mv' command

I want to rename my file to the current timestamp.I know how to get the current timestamp("date +%s") but how can I pipe it to 'mv' command?
4
votes
2answers
630 views

List files created on Sundays

How do I list/find all the files created on Sundays or Mondays? How do I use the date parameter to display them? Something like : ls -f date + %a or find -type f | date +%A or find -type f ...
4
votes
1answer
6k 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 ...
4
votes
5answers
2k views

Padding a number in a filename to a fixed length

I have a directory of files such as: file.1.png file.2.png … file.10.png … file.1000.png file.1001.png … How can I pad the number to 4 digits? It should end up like this: file.0001.png ...
4
votes
3answers
4k views

In a regular expression, which characters need escaping?

In general, which characters in a regular expression need escaping? For example, the following is not syntactically correct: echo '[]' | grep '[]' grep: Unmatched [ or [^ This, however, is ...
3
votes
3answers
247 views

How do I find a file with a name which depends on the current date (and a random component)?

I have to check a particular path every day and find the file with a name of the form: StaticData_Sets_yyyymmdd-232550.txt The date in the name after the string StaticData_Sets_ is updated every ...
3
votes
2answers
919 views

Changing tmux .bash_profile behavior

I have a script in my .bash_profile that prompts for X sessions to boot. When I launch tmux, I get this prompt that I had only intended for the TTY login. Is there something I can put in ...
3
votes
4answers
459 views

Piping paths with different types of quotes for slash substitution

I would like to use sed to convert a path with backslashes to the same path with forward slashes: E.g. I would like to pipe \\path\to\file\ and obtain /path/to/file None of the following commands ...
3
votes
1answer
1k views

creating abbreviations for commonly used paths

I am new to linux and was wondering whether it is possible to create abbreviations that can be used in terminal. I know about alias command, but am not sure whether that can be used for what I am ...
3
votes
2answers
2k views

Change directory with -d in shell script

I am trying to give the option to the users to run the script in a different directory. However when the script changes the directory, the mkdir does not work. I change the directory like this: case ...
2
votes
2answers
1k views

Changing user to root when connected to a linux server and copying files

My script is coded in a way that doesn't allow you to connect to a server directly by root. This code basically copies files a server to my computer and it works but I don't have access to many files ...
0
votes
1answer
6k views

mounting problem during installation of archlinux on dell xps one

I've been trying to install archlinux on xps one. the screen doesn't work because it has intel g45/g43 express chipset. I had to use nomodeset option as mentioned in the installation guide. Arch ...
19
votes
6answers
697 views

Why is aliasing over standard commands not recommended?

For example, a common alias I've seen in the ~/.bashrc file (or equivalents) is alias rm='rm -i' However, I've seen people recommend against this because the alias might not exist on another ...
12
votes
3answers
3k views

How do you process an entire command as sudo that involves redirecting or piping?

I am trying to follow what I assume is best practises of using sudo instead of root account. I am running a simple concat file operation such as: sudo echo 'clock_hctosys="YES"' >> ...