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, …).

learn more… | top users | synonyms (1)

2
votes
2answers
83 views

Filtering a file on a string

I have a file which looks like this a 0 gene1 56 0 6S32M12S * b 256 gene2 56 0 6S32M12S * c 256 gene3 55 0 6S27M17S * d 16 gene4 110 9 19S25M6S * e 272 ...
1
vote
1answer
37 views

How does executing a file change the std input?

Imagine I have a script, which contains the goto command. The goto command will search in the std input for a line like this : jumpHere. But the std input is by default the terminal. It only makes ...
6
votes
2answers
860 views

Was there a '\0' at the end of every script?

I'm wondering how did you dertermine the end of a script/file? I'm especially interested for old Unix versions (like V6). Is there a '\0' after the last written character?
3
votes
2answers
63 views

terminal warn on close when opened within a script

First, the question: How can I warn the user that a script is running when the user clicks the close button and the terminal itself (and the process running in it) was started from the command line. ...
2
votes
2answers
41 views

Changing variables in a forked process from outside that fork?

In theory with this block, you should only see "running..." once(or less), but in practice, it repeats until it's manually killed. How do I change the value of x inside the forked process to false ...
1
vote
0answers
25 views

optimisation of bash globs

Looking for a guide to optimising regexp matches in bash. I have a script that loops over a very long list of URLs looking for patterns. Currently it looks a little like the fragment below. Is there ...
0
votes
0answers
7 views

trying to run a windows program with Crossover on my mac

I installed the program through wine and it made a bottle for the windows program. When I try to launch it I get the following error: "The COM library could not be initialized." Please help? What ...
2
votes
1answer
77 views

Avoid backslash expansion with echo in dash

First create a file with this exact content: a\nb I named this file foo, if I run the following, it prints the exact content of the file: bash -c 'bar=$(cat foo);echo "$bar"' But if you run it ...
-2
votes
3answers
63 views

Why do I get “integer expression required”?

I'm trying to have a small function that I then call. To keep it simple I just want to validate that 12 is divisible by 2,3 and 4 The code is: divisible_by () { under_test=12 from=2 to=4 ...
1
vote
3answers
92 views

How could I reach root after switching from bash to zsh?

It's very weird that after switching to zsh from bash, I can't access root. I normally use 'su' to login as root after I login as a normal user (username is normalusername) with less privileges. And ...
2
votes
2answers
101 views

output both stderr and stdout on console and store them in a file at same time

may I output both stdout and stderr on console screen and store one of them into a log file? I write a test shell script: #!/bin/sh echo OUT! >&1 echo ERR! >&2 I can output both of ...
2
votes
0answers
54 views

fork and wait - Unix v6 [migrated]

Here is the last part I do not understand in the source code of old unix v6 command if. Source: http://v6shell.org/history/if.c, with Syntax-Highlighting: http://pastebin.com/bj0Hvfrw if(eq(a, "{")) ...
3
votes
2answers
44 views

Test if valid executable

Is there a (relatively) simple way to test if an executable not only exists, but is valid? By valid, I mean that an x86_64 Mach-O (OS X) executable will not run on an ARM Raspberry Pi. However, ...
2
votes
1answer
69 views

Behaviour of 1>&0 in bash

So I am trying to learn more about file descriptors and their redirections. At the moment I am exploring an edge case of doing 1>&0 and I cannot quite understand what is happening there. $ ...
34
votes
2answers
4k views

Why is using && 75 times faster than if…fi and how to make code clearer

I have the following working code: largest_prime=1 for number_under_test in {1..100} do is_prime=true factors='' for ((divider = 2; divider < number_under_test-1; divider++)); do ...
0
votes
0answers
35 views

PHP “Output file write error” with shell_exec and stdin (|)

php -a echo shell_exec('djpeg image.jpg | pamfile'); result: Output file write error --- out of disk space? stdin: PPM raw, 500 by 373 maxval 255 (djpeg converts a jpeg to PPM and writes to ...
0
votes
1answer
36 views

How i make this script execute every minute without cron? [duplicate]

I have this: #!/bin/bash wlan=`/sbin/ifconfig wlan0 | grep inet\ addr | wc -l` if [ $wlan -eq 0 ]; then echo wlan0 not connected, connecting... echo sudo ifup wlan0 logger wlan0 reconnected. echo ...
5
votes
0answers
49 views

HURD: Why is remote process not killed?

On most UNIX systems this will not leave a process running: ssh example.net sleep 1000 <<CTRL-C>> I have tested this behaviour on aix centos debian dragonfly freebsd hpux irix mandriva ...
93
votes
7answers
11k views

How to kill a runaway cat?

Many times I accidentally run the cat command on files have contents up to few thousand lines. I try to kill the cat command with Ctrl+ C or Ctrl+Z, but both only take effect after the total output ...
4
votes
3answers
144 views

Using | pipe character from a $variable makes it treat as just another argument in bash; how to escape it?

I have a bash script like this export pipedargument="| sort -n" ls $pipedargument But it gives the error ls: |: No such file or directory ls: sort: No such file or directory It seems to be ...
0
votes
1answer
44 views

From Mysql query output to retrieve files in the file system and rename the files

I have to call a SQL query from bash that outputs 1000 rows of two columns File_Path (Eg., /opt/files/dest/2.bin) Name_of_the_file (Eg., fax attachment.pdf, invoice.docx... yes, there are spaces). ...
2
votes
2answers
82 views

Feed source command with a pipe

Previously I used source command like this: source file_name But what I'm trying to do is this: echo something | source Which doesn't work.
3
votes
1answer
64 views

GUI terminals(?) reset $SHELL

I've been playing around with the fish shell for a few days and I like it. In order to start fish in a terminal via a quicklauncher or menu, I'm using a script like this:1 #!/bin/sh export ...
1
vote
1answer
29 views

Remotely connect to computer when connection partly fails

I have a Debian computer acting as a server at home. It has a dovecot+postfix mail server, an SSH server, an apache server, and everything you would expect from a do-everything server. At home, it is ...
1
vote
3answers
75 views

Compare two files and print unmatched lines [duplicate]

I have two files with the below data; I need the difference between two files. I tried with diff but it also shows line which are common in the two files: (22372 Dec 4 15:36 ...
0
votes
2answers
52 views

Combining two bash script and using a menu

I have two scripts, one that is used on a folder with csv files and another on a folder with .tar.gz files. In the second script, I first unzip the files before doing anything with them. Now I want to ...
0
votes
1answer
63 views

linux/shell command to control screen brightness in android

I am working on a kiosk project using an android tablet.If there is no input power to the kiosk for a long time then, the tablet will eventually shutdown.In order to auto-reboot the tab when the power ...
3
votes
1answer
63 views

Copy only file details (file name, size, time) from remote machine in unix

how can we copy only file details (filename, size, time) from a remote machine in Unix? For example: I have a directory (/opt/apache/…/webapps/Context) placed on a remote machine. Now I want to copy ...
5
votes
3answers
156 views

Echoing stdin when running an ed(1) script

Given the following ed script, $ cat helloworld a hello world . ,n ,s,o,O,g ,n Q I would like to obtain somehow the interactive output $ ed a hello world . ,n 1 hello 2 world ,s,o,O,g ,n 1 ...
1
vote
3answers
47 views

Running background process with screen command in xshell

screen command is a nice program for us to run process background, but I found Ctrl + a w do not show screen windows list in xshell(Xmanager component) and Ctrl + a k do not kill this screen terminal ...
1
vote
1answer
76 views

View a command in the shell history [closed]

If we put a space before any command in the shell it will not shown in history. Is there any way to see that command if the user enters a space before any command?
4
votes
2answers
164 views

Running commands stored in shell variables

The following works in my shell (zsh): > FOO='ls' > $FOO file1 file2 but the following doesn't: > FOO='emacs -nw' > $FOO zsh: command not found: emacs -nw even though invoking emacs ...
1
vote
3answers
69 views

How to send input in a new terminal using Shell Script

I found out how to automatically send input to a C program using Shell Script. For example, if I compile this C program: //test.c int main() } int x; printf("Please enter an integer:"); ...
1
vote
2answers
65 views

Passing a command with arguments to a script

I am trying to write a shell script that receives as an input a command with arguments and runs it. As an example, I am hoping to use this in cron as follows: 0 11 * * * my_wrapper.sh "task_name" ...
1
vote
1answer
55 views

Redirection differences between &> >& and 2>&1

On this SO thread and a few other threads I have seen the following commands for redirecting stdout and stderr to a file. Are they all equivalent? Is there any difference between them? command1 ...
6
votes
4answers
225 views

Command line shortcuts for changing directory

I'm looking for an easy way to navigate to directories spanning multiple hard drives and want to set something equivalent to a shortcut within the terminal. In Windows I would accomplish this with ...
1
vote
2answers
58 views

How can I replace bash using Python?

According to the accepted answer for this SO question: , Python can make a great bash replacement. My question then, is this: how do I go about seamlessly make the switch? I think the main thing to ...
1
vote
3answers
66 views

Extract lines with specific dates and execute a command on each of them

I'm using a Google Drive command-line script that can return a list of files such as: Id Title Size Created 0Bxxxxxxxxxxxxxxxxxxxxxxxxxx ...
3
votes
0answers
37 views

Rename file with the name from a variable [duplicate]

I want to rename an image with the text in that image. For that I use an OCR and I try to store the name in a variable and use that variable in the mv command but I get mv: target ‘file’ is not a ...
8
votes
3answers
339 views

How can I list all shell variables?

Reading about this question: In zsh how can I list all the environment variables?, I wondered, how can I list all the shell variables? Also, does the distinction between shell variables and ...
2
votes
1answer
25 views

Default shell in Oracle Linux?

bash is default shell for Red Hat Linux Distribution. In the same way, what is the default shell in Oracle Linux? I tried to find this by executing [root@serverName ~]# sudo $SHELL But, I did not ...
1
vote
1answer
20 views

Switching shells for one cron job

Say I have the following in my crontab: * * * * * command1 -option A; command2; command3; etc. I would like cron to run the commands I have in that line with a specific shell. How can I do that? ...
3
votes
1answer
61 views

manual questions

Hey :) I am trying to understand the command goto. I have some questions regarding the goto manual. Here you can find the original manual: http://man.cat-v.org/unix-6th/1/goto 1. Goto is allowed only ...
1
vote
3answers
62 views

Iterative Control Flow in Subshelled Script [closed]

I have a shell script(A) that is being called by another script(B). In this script(A) I am creating some directories and moving some files as preparatory work for the rest of the script to work fine. ...
2
votes
1answer
21 views

Pipelines, Jobs and Processes in Zsh

I went through the Jobs & Signals documentation in Zsh, but some things aren't still clear to me. It says: If the MONITOR option is set, an interactive shell associates a job with each ...
1
vote
1answer
24 views

Get chronological list of dates & times for scheduled tasks in cron

Given a job specification in crontab, is there any way to get the list of dates and times the job in cron will run in the next week? For example, given a string 10 13 * * *, is there any way to get ...
2
votes
1answer
63 views

Why string comparision results always false

I am trying to do a one time check about apache's mod-status page for updates like this(this is just a test script): firstcontent=$(lynx -dump http://some-server/server-status-page) echo ...
2
votes
1answer
65 views

Problematic bc calculation in shell script

On Ubuntu 14.04.1 64-bit LTS I am writing a shell script and if I define the start of the sequence used in the for loop with a variable instead of a constant I get really weird behavior and there are ...
0
votes
2answers
56 views

Bash Script Parsing Argument not working correctly

i have the following bash script (taken from FFmpeg) #!/bin/bash ################################################################################ # # Script name: MultiMedia Concat Script (mmcat) # ...
2
votes
2answers
32 views

Bash globs as non-file arguments. Example: apt-get remove pkg-*

I know * and other glob patterns are transformed into words by pathname expansion, based on the current working directory. Hovever, some commands seem to use them for non file arguments. For example, ...