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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11
votes
2answers
294 views

Why does cat x >> x loop?

The following bash commands go into an infinte loop: $ echo hi > x $ cat x >> x I can guess that cat continues to read from x after it has started writing to stdout. What is confusing, ...
1
vote
2answers
117 views

Find doesn't want to find *.sh in certain level [duplicate]

I have a problem with find. It doesn't find *.sh files if I am in certain directory level. It does, however, find *.sql files. /path$ cd do_not_upload/updates/1.1.1/ ...
4
votes
3answers
216 views

How do I capture stdin to a variable without stripping any trailing newlines?

In a shell script... How do I capture stdin to a variable without stripping any trailing newlines? Right now I have tried: var=`cat` var=`tee` var=$(tee) In all cases $var will not have the ...
48
votes
5answers
2k views

cd by just typing the directory's name?

I either had this somewhere 20 years ago or I dreamed about it. Basically: If if type blobblob I get blobblob: command not found Fair enough. I would like it so that when my shell gets those ...
9
votes
2answers
5k views

What is the significance of single and double quotes in environment variables?

I defined some environment variables in my .profile like this: MY_HOME="/home/my_user" but the variable does not seem to evaluate unless I strip off the quotes and re-source the file. I believe ...
12
votes
6answers
1k views

What is the reverse of echo -e?

If I have a string with nonprintable characters, new lines, or tabs, is there a way I can use echo to print this string and show codes for these characters (e.g., \n for new line, \b for backspace)?
1
vote
1answer
79 views

Is autocompletion for applications done by shell?

When I type evince, and then hit tab, the bash shell will list all files that can be opened by evince, which seems to be based on the ext part of the filename. Is this done by shell or the ...
4
votes
2answers
1k views

how to make alias to make grep command shorter [duplicate]

In my coding, I always do grep -rnIi "abcabc" . --color But, how to make an alias that can let me type only one word with my search string? Is that possible?
5
votes
5answers
4k views

Check if script is started by cron, rather than invoked manually

Is there any variable that cron set when it's running a program ? If the script is running by cron, I'll skip some parts; otherwise invoke those parts. How can I know if the bash script is started by ...
2
votes
1answer
290 views

Can you change timestamp format for history command on tcsh

When I run history command (on tcsh), it only prints the TIME portion of the timestamp and omits the date: 3 15:07 echo $PATH 4 15:07 ls -la In bash, you can use HISTTIMEFORMAT ...
2
votes
1answer
11k views

unexpected EOF while looking for matching `"' - bash script

I just wrote a bash script (im a Newbie to shell-scripting ;) ) and always getting this EOF-Error. So here is my script (only works on OS X): #!/bin/bash #DEFINITIONS BEGIN en_sq() { echo -e ...
4
votes
1answer
161 views

How to catch a signal in command line?

I asked this question. SIGPIPE signal is generated to stop the execution of the command as told in the answer. But how do I capture this signal and gracefully terminate the command? The command exits ...
1
vote
5answers
104 views

Is there a way to find out the number of lines from a command output?

I am trying to compare command outputs between two servers. I want to find out the number of lines from the output of commands such as ls -l. Is there a way to do so? So far I have not found anything. ...
1
vote
2answers
94 views

Run command on startup for one user

I made a new user on my server. The user is not logged into the bash shell on startup. To do this I can run /bin/bash --login and it works. Where do I place this command so that it runs ...
1
vote
1answer
168 views

$PATH environment variable does not seem to be recognized

I've made a fresh install of Debian Wheezy, and installed zsh to it. Few days after, I've done a vanilla installation of TeX Live 2014, so I added the necessary binary paths to my $PATH. Now I started ...
0
votes
2answers
72 views

Find an archive and extract it in the directory where it is located

I want to find a tar file which is presented in any directory and un-archive it in a one line command. I am able to find it separately from home directory. but only can extract it from directory ...
5
votes
2answers
260 views

echo of a string with an exclamation point

Here are what I put in bash and the results I got about 'echo': $ echo '!$' !$ $ echo "!$" echo "'!$'" '!$' I'd like to know how 'echo' deals with the second input. It seems to me that ...
2
votes
2answers
124 views

Regarding getting Date - n days Date

Suppose I have a particular date stored in a variable (date_m) . I want ((date_m)-25) date. For eg: I have 15/09/2014 stored in my variable , then I want 21/08/2014 returned if I subtact 25 from the ...
1
vote
0answers
282 views

Cannot SSH after switching to Netgear router

I have Comcast Xfinity internet. When I was sent their Wifi router/Cable modem combo box, I was able to use SSH perfectly. However, since the Wifi from the box was weak, I decided to buy my own ...
5
votes
2answers
128 views

bash crashed with for loop [duplicate]

The question may be trivial but with this simple for loop for i in {1..10000000}; do echo "$i" line >> file done my shell crashed after some elaboration time (the tab in the terminal emulator ...
2
votes
3answers
87 views

When was the script started?

What I want is, -bash-3.2$ ps -aef | grep 29137 jeeadm 9794 1190 0 09:22 pts/2 00:00:00 grep 29137 jeeadm 29137 1 0 Sep02 ? 00:00:21 Java Second Row, Fifth Column entry, as in ...
15
votes
3answers
1k views

why 'echo --help' doesn't give me help page of echo?

I tried 'man echo' in Bash and it told me that 'echo --help' will display help then exit, and similarly, that 'echo --version' will output version and exit. But why it doesn't work ? 'echo --help' ...
1
vote
3answers
434 views

Execute a file if a command is not found

When I try to execute files in Linux, I'm always annoyed by the need to write ./executablefile instead of just executablefile. I get why it's done, so it won't have an ambigous input, one that is a ...
1
vote
2answers
63 views

Difference in output from shell script

I am running a simple shell script which has a for loop and kicks off 16 threads in the back ground and waits for each of them to finish before moving on the next commands. Here is the shell: ...
0
votes
1answer
83 views

in Shell Scirpt I want to use ::ssu <USERNAME>

I want to ssu or alternate command in shell script. However it's asking for password in middle of shell script. I don't want to do that. Any alternate command or suggestion? E.g. ssu ...
7
votes
3answers
2k views

How to stop Fork Bomb out of memory error - RHEL 6

I set up test VM to test the effect of fork bombs. So I edited the limits.conf as follows for root user: root hard nproc 512 Now I drop a fork bomb like so: :(){ :|:& };: After ...
11
votes
5answers
19k views

Is there a way to set the size of the history list in bash to more than 5000 lines?

No matter how much I set the HISTSIZE environment variable to be larger than 5000, when printing the history list with the history builtin, it prints only the last 5000 commands. I need that because I ...
1
vote
0answers
621 views

Load a background image or set the background color if Konsole/Shell is running SSH

I want to set my laptop to load an image in the shell's background or set the background color to red if I'm connected via SSH. How can this be done? With a bash function in .bashrc? I have: Set the ...
24
votes
6answers
11k views

determining path to sourced shell script

Is there a way for a sourced shell script to find out the path to itself? I'm mainly concerned with bash, though I have some coworkers who use tcsh. I'm guessing I may not have a ton of luck here, ...
1
vote
4answers
200 views

why do we not need export here?

$ IFS=";" $ read first second i am;a_i b c $ echo $first i am $ echo $second a_i b c $ echo $IFS Am I right that read first second is a subprocess of the current shell process? If yes, why don't ...
1
vote
2answers
197 views

Apply given rsync exclude patterns on given directory

I have a setup where I use rsync to mirror some source directory to a (remote) destination except for some files and locations defined witch rsync exclude patterns: # Useless files - thumbs.db - *.~ ...
1
vote
1answer
57 views

Can I start a background process with a specific working directory?

Say I have this structure /masterscript /a/script1 /a/b/script2 In masterscript I spawn the other scripts as background processes: "/a/script1" & "/a/b/script2" & The problem is that ...
0
votes
1answer
198 views

Running shell script on cluster in parralel

I thought dsh(Distributed Shel) will be a good option but when i ran my shell script across my nodes, I didnt get expected output, dsh -aM -c bash /home/cloudera/bash_script.sh server2@x.x.x.110: ...
22
votes
1answer
27k views

How to loop over the lines of a file?

Say I have this file: hello world hello world This program #!/bin/bash for i in $(cat $1); do echo "tester: $i" done outputs tester: hello tester: world tester: hello tester: world I'd ...
2
votes
1answer
320 views

How to sort files based on the json property value inside the file?

I've downloaded list of videos via youtube-dl and each file has corresponding .json file containing certain properties. So I would like to sort the files based on the selected json property which is ...
0
votes
1answer
111 views

How to automate ktutil to immediately list keytab entries?

I use MIT ktutil a lot on Linux and I am fed up using the following sequence, even if command shortcuts and file name completion are here to help: ktutil rkt my.keytab l Isn't there a way to get ...
5
votes
3answers
481 views

cd to directory of a symbolically linked file

Before I write a script, anyone know an easy way to do the following: $ pwd /foo/bar $ ls -l lrwxr-xr-x 1 username admin 48 Apr 17 2012 foo.sh -> /bar/foo.sh $ cd /bar $ ls foo.sh i.e., in ...
7
votes
2answers
965 views

Bash string concatenation used to build parameter list

Given this piece of bash: PARMS='-rvu' PARMS+=" --delete --exclude='.git'" echo $PARMS rsync ${PARMS} . ${TARGET} The echo shows the PARMS string as expected, no error is displayed, but rsync ...
7
votes
2answers
16k views

Why does source give an error “cannot execute binary file”

I have small file that does initialize a tmux session and then creates some windows. After some debugging and tweaking things worked fine until I renamed the text file (with the tmux commands) from ...
1
vote
0answers
136 views

How to start a process chain from the shell

Is it possible and if so how do I: Start a /bin/bash process that is not bound to a terminal from a terminal? Hence, a shell process that shows up in the process tree as init -- bash. (Shells ...
2
votes
0answers
95 views

How can you get the current terminal line (the one that is still editable by the user)?

I need a way to use the current line which the users typed into as variable for a shell function. my current code, which can be called by ctrl+r zle -N search bindkey "^R" search search () { read ...
0
votes
2answers
222 views

Login by ssh , exec one command and i don't want to quit the bash

I want to change PS1 when i ssh another centos strshell = 'PS1="remote!"' os.system("ssh -i %s -l%s -p%s %s %s"%(SSH_KEY,SSH_USER,SSH_PORT,des,strshell)) ssh quit automatically. I want to ...
10
votes
1answer
538 views

How to “correctly” start an application from a shell

I find it hard to phrase the question precisely but I will give my best. I use dwm as my default window manager and dmenu as my application launcher. I hardly use GUI applications aside from my ...
1
vote
2answers
135 views

Passing print pattern as a variable to awk

I am trying to use awk to print variables from various columns in a line delimited by , .The columns and pattern which I want to print is stored in another variable b. The pattern a and print patter ...
1
vote
1answer
177 views

Pattern replacement

Please can anyone explain to me in brief the syntax of this command. Explanation in terms of how actually this command is written significance of each and every character used. I know the output of ...
2
votes
2answers
131 views

How do you get a count of all file extensions on a hard drive using the gnu+linux terminal? [duplicate]

On windows I have a program that can count all the files on a hard drive and the output shows a list of file extensions and a number (which showed how many files on the drive were for example are ...
4
votes
2answers
9k views

How to list ALL directories according to their size? [without including the parent directory]

I have a bunch of random folders, some of them are hidden (beginning with a period). I want to list all of them, sorted by their sizes. I have something on the lines of this in mind: ls -d -1 -a */ ...
2
votes
3answers
2k views

Saving individual output lines into variables

I'm using find -mtime -2 to find files modified in the past 24 hours or less. The output looks like this. /home/user/logs/file-2014-08-22.log /home/user/logs/file-2014-08-23.log I need to save the ...
1
vote
2answers
62 views

Confusions mitigation while working similar environments in multiple servers

I often have to open multiple ssh sell terminals of remote servers together., eg. Dev and test. These paths and applications are exactly similar. And I am often confused if I run a particular command ...
8
votes
2answers
3k views

How to download an archive and extract it without saving the archive to disk?

I'd like to download, and extract an archive under a given directory. Here is how I've been doing it so far: wget http://downloads.mysql.com/source/dbt2-0.37.50.3.tar.gz tar zxf dbt2-0.37.50.3.tar.gz ...