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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4
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3answers
1k views

Reading a binary file as an array of bytes or 16 or 32 bits using shell script

I am working on ARM-based modem Linux host machine and I need to read a bin file as an 8-,16- or 32- bits array. I basically need to encrypt the file in question and was thinking of just XOR-ing the ...
2
votes
3answers
1k views

how does built in commands of a shell implemented in Linux? as a function or thread of shell process?

I know that external commands are run in the shell by creating a separate process. But what exactly happens when a built in command is run in a shell. Are they executed as a function or if the shell ...
0
votes
3answers
117 views

Is there a way to switch to “su -” after switching users through “su”?

Maybe the title wasn't worded quite clear. But basically what I want to be able to do is to switch to having used "su -" instead of the traditional hyphenless "su" after already using "su" to switch ...
3
votes
3answers
5k views

Why do 'ssh host echo $PATH' and printing the $PATH after ssh'ing into the machine give different results?

On a particular host, when I ssh into the machine and enter echo $PATH I get /home/wxy/bin64:/home/wxy/bin:/usr/kerberos/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/local/bin:/bin:/usr/bin and if I ...
4
votes
2answers
51k views

“not a valid identifier” when I do “export $PATH”

When I run export $PATH in bash, I get the error not a valid identifier. Why?
8
votes
2answers
5k 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 ...
1
vote
0answers
617 views

Easy way to push data into MongoDB from Bash shell script?

I know you can create a Javascript file that the MongoDB shell will execute upon startup. But I'm hoping for something more "lightweight" than that. I am using a Linux program that has a scripting ...
6
votes
3answers
2k 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 ...
11
votes
2answers
7k views

Executing piped commands in parallel

Consider the following scenario. I have two programs A and B. Program A outputs to stdout lines of strings while program B process lines from stdin. The way to use these two programs is of course ...
7
votes
3answers
32k views

Terminating a bash shell script running in the background

I often use bash shell scripts to run simple commands for many different files. For example, suppose that I have the following bash shell script, called script.sh, that runs the program/command foo ...
-2
votes
1answer
503 views

SED command and filenames with space

I was hacked, for my php files was infected. Example: http://www.nwww.ma.mk/oscommerce/configweb/apexfash-wp-blog.txt Bad Code: <?php $zend_framework="\x63\162\x65\141\x74\145\x5f\146\x75\156\...
0
votes
2answers
295 views

Why are there empty lines in the output of my command?: find ~/x/y/ | shuf > ~/Desktop/z.txt

As it turns out the reason for this problem was one filename with several newlines. (No idea how that happened.) find ~/x/y/ | shuf > ~/Desktop/z.txt This command works pretty much as expected ...
4
votes
2answers
1k views

Convert MAC address to Link-local address with bash

How can I convert a Mac address into an ipv6 Link-Local address? you have to add fe80:: at the start and insert ff:fe in the middle furthermore all leading zeros must be stripped
5
votes
2answers
12k views

how to loop through arguments in a bash script

I would like to write a bash script with unknown amount of arguments. How can I walk through these arguments and do something with them? A wrong attempt would look like this: #!/bin/bash for i in $...
4
votes
4answers
548 views

How to deal with spaces in a variable

I'm working on some scripting: for x in `find ./ -name *.pdf` do echo pathname $x done My filenames are Test1 ( Volume II), Test2 ( Volume II). I'm getting a return of pathname Test1 pathname ( ...
-1
votes
1answer
63 views

Strange combination of symbols UNIX [closed]

I was looking at one korn shell script examples and I saw this strange combination of symbols: %? So my question is what does it mean?
4
votes
2answers
391 views

Do redirection operators always open file descriptors in parallel?

1. Consider snippet#1: $ cat test.txt > test.txt cat: test.txt: input file is output file It seems that cat makes its input file descriptor point to test.txt and then when it tries to set its ...
2
votes
1answer
254 views

Is there a text-only equivalent (no curses) of `zenity --question`?

For my mercurial commit hook, I want to run my test cases and be asked whether I really want to commit if any of the tests fail. I'm thinking something like <run-the-tests> || <ask-yes-no>...
6
votes
2answers
1k views

Quoted vs unquoted string expansion

for i in $(xrandr); do echo "$i" ; done for i in "$(xrandr)"; do echo "$i"; done for i in "$(xrandr)"; do echo $i; done I understand why 1 differs from 2. But why does 3 give a different output ...
1
vote
2answers
3k views

Shell hangs when doing command from ssh

I'm trying to automate a server update process. What this should do is check for git diff files and list them, to later be copied from one place to the other. Here's my script on my local machine: ...
7
votes
10answers
29k views

Bash way to check if a process is already running in the background (and skip re-execution based on that)?

Can I make a bash command line that only runs a certain command if the process is not already running (in the background)? How do I check*, if a command is already running? (so I can add the next ...
3
votes
4answers
172 views

$PATH duplication issues

If I do echo $PATH I get the following: /usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/usr/local/share/npm/bin:/usr/local/share/python:/opt/X11/bin:/Users/kh/.rvm/bin:/usr/bin:/bin:/usr/sbin:/...
2
votes
2answers
1k views

Debugging bash functions [closed]

So here I have a simple function that I wish to debug. However, I am unable to debug the desired function even with set -o functrace enabled. Before resorting to asking this question, I had managed ...
3
votes
1answer
2k views

How can I convert this bash function to the fish shell

I'm trying out the fish shell 2.0 to replace bash. I'm trying to convert the following bash function to a fish function, but its giving me hell. I have a several similar functions so if someone ...
3
votes
1answer
455 views

Cron job results are different from executing from own shell

I am using Ubuntu 12.0.4 I have a script basically with the following codes: lockfile=/var/tmp/mylock if ( set -o noclobber; echo "$$" > "$lockfile") 2> /dev/null; then exit_normally "...
6
votes
3answers
1k views

How to alias cp with cp -i by default

Is there a good way to alias the command cp file1 file2 to cp -i file1 file2? Apologies if this is a dumb question, I'm a Unix novice.
2
votes
5answers
14k views

Carriage return issue

I have this in a bash script DAY2="20130605"<Cr> echo "This is yesterday date:"$DAY2"end" Why is the output the following? It seems as though there is a carriage return in DAY2 but where is ...
3
votes
3answers
2k views

How to make my tmux which starts via crontab @reboot use bash?

I have a crontab which launches tmux-launching-script as follows : -sh-3.00# crontab -l @reboot /root/scripts/tmux_autostart.sh where #!/bin/bash # setup tmux session tmux new -d -s my_session ...
14
votes
3answers
3k views

Which is more idiomatic in a bash script: `|| true` or `|| :`?

I don't do terribly much shell scripting, so I was a little surprised when I was reading the documentation for git submodule and I saw the syntax they used in this documentation: A non-zero return ...
2
votes
1answer
932 views

7z getting an event not found error in command line

I am using 7zip on my centos machine and ziping a file via command line. This is my syntax 7za a -t7z backup.7z public_html\ -mx0 -xr!restricted_area What i'm expecting with this syntax is to ...
19
votes
5answers
29k views

In linux, how to delete all files EXCEPT the pattern *.txt?

I know how to delete all txt file under current directory by rm *.txt. Does anyone know how to delete all files in current directory EXCEPT txt file?
2
votes
4answers
7k views

sh and grep numbers only

I'm facing a problem and trying to find a solution that works in sh. If I could use bash this code would work: ls /a|grep ^[0-9] Unfortunately this is not the case with sh, and yes I need to use sh....
3
votes
3answers
2k views

How to use arguments with 'find -exec'? [duplicate]

I'm trying to generate static html files for all php scripts inside dir: find . -name "*.php" -exec php {} > {}.html \; But it just dumps all results to {}.html. How to do it properly? And how ...
5
votes
3answers
1k views

How can I background a shell script during a Kickstart?

I have a Red Hat Kickstart process which reports its progress at key points via a POST request to a status server. This is fine during %pre and %post, but when the actual build is taking place ...
2
votes
3answers
15k views

Get environment variable of other user [closed]

Is there a way I can see the environment variable of an other user? I want to do that as root, so permissions won't be a problem I guess. For the user himself, I use echo $PATH or set | grep PATH (...
0
votes
1answer
512 views

How to identify error in a particular file while checksum verification (which file having problem while verification) in shell script

I have two files on ftp location in csv.gz format and their checksum is in .csv.gz.md5 format. I am copying this file in my local system. I am generating check sum for it through md5sum. Now I am ...
1
vote
1answer
3k views

when to use double quotes with a variable in shell script? [duplicate]

I am in a confusion with what is meant by the double quotes referring to a variable. For example following two scripts gives the same output. What is really meant by the double quotes? Script1 ...
0
votes
0answers
28 views

Parameters of script [duplicate]

how can I make my script to work like that: "scriptname.ksh -p file, -n UserName". I mean how can I set my script to work with 2 parameters defined by "-p" and "-n" characters?
1
vote
0answers
1k views

service command: Failed to issue method call

I downloaded the source of tinyproxy and then use ./configure make make install to install it Then I want to start it, but get errors, like the following: [root@kitty tinyproxy-1.8.3]# service ...
4
votes
2answers
170 views

Is it possible to restrict certain commands from being run in a directory?

I have two directories: src and projects. I would like to prevent myself from running git ... unless I am specifically inside src or projects. Is this possible?
1
vote
2answers
696 views

Running a bash script within a bash script

I am writing a bash script for the installation of an environment manager but it means that I have to install something within multiple directories. See my other question for more details. But this ...
0
votes
1answer
320 views

Bash script installing within multiple directories [closed]

I am attempting to write a bash script that will install rbenv from beginning to end. I am on a Mac for interest sake. But there are some things that are not working mainly i am changing the ...
1
vote
0answers
179 views

add audio from playing file to microphone stream

I need to add a sound to what the microphone is capturing, is it possible? I started with man aplay and found that I can do aplay -D PCMdevice filepath.wav so then I listed the PCM devices with ...
2
votes
1answer
2k views

Cut + Copy + Paste in Linux Puppy Wary

Trying to cut + copy + paste from the standard urxvt shell in Puppy Linux Wary 5.3. If I follow this post on http://crunchbang.org/forums/viewtopic.php?id=15085 and I press: in urxvt: ctrl + ...
15
votes
3answers
2k views

Why not use pathless shebangs?

Is it possible to have a shebang that, instead of specifying a path to an interpreter, it has the name of the interpreter, and lets the shell find it through $PATH? If not, is there a reason why?
1
vote
1answer
216 views

How to stop CACHE instance from Shell Script

I want to restart CACHE(database that I am using) Instance from shell script. What I did is created a function in the shell script named resatrt_cache. restart_cache() { ccontrol stop instancename ...
2
votes
1answer
1k views

broken pipe error with popen and JS ffi

I am using a ffi for nodejs which for the most part has nothing to do with this question which is really about understanding pipes better, but does offer some context function exec(cmd) { var ...
3
votes
1answer
109 views

find utility does not recognize bracket notation

I've two files in the current folder: submitWeb.m submit.m the following find does not show the two files: find . -regex .*submit\(Web\)?\.m But the above regex expression works fine in ...
103
votes
5answers
97k views

How do I use pushd and popd commands?

What are the practical uses of both pushd and popd when there is an advantage of using these two commands over cd and cd -? EDIT: I'm looking for some practical examples of uses for both of these ...
3
votes
2answers
36k views

mv: cannot stat No such file or directory in shell script

I wrote a script to move some files form one folder to another folder but I got the following error, I checked 2 folders and notice for 1 folder there are such files and another there is no such files,...