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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3
votes
1answer
373 views

Conditionally killing a process based on its output

I have a REPL (read-eval-print-loop) for the Clojure programming language listening on a network socket. I can send it code over the network and the code will be evaluated and the answer sent back to ...
3
votes
2answers
266 views

Advanced usage/command of shell [duplicate]

Possible Duplicate: Is there any book , Tutorial on very very advanced shell scripting Is there a way/book to learn advanced usage of shell by practice? I find that most shell programming ...
4
votes
2answers
3k views

How to escape < or > in a parameter in shell?

I'd like to use grep with a PCRE expression that contains the < character. Bash thinks I want to redirect, but I don't want to. How can I escape <?
3
votes
2answers
221 views

ln gives different results when run multiple times

I have this simple script to use with seventh sense (it's a lone wolf gamebook reader/player): #!/bin/bash GAME_PATH=$(dirname "$(readlink -f "$0")") SEVENTH_SENSE_PATH=$(echo ...
3
votes
3answers
389 views

Kill process when it stops to produce further output

Is there a shell tool which can probe if a subprocess is still producing output, and otherwise kill it after a specified timeout? I'm using offlineimap for Gmail backup, but that's very very very ...
2
votes
2answers
464 views

Want a seperate file to store mysql username, password, and database name

I have as script that dumps a mysql database, and compresses the file. What I want to do is have another (edit) file which can change the username, password and database name. Then somehow connecting ...
7
votes
2answers
811 views

Piping output from a segfaulting program

I have a script that calls a program (specifically, ttf2afm, part of tetex 3.0) that sometimes segfaults and sometimes doesn't. The information I need is always printed out before it segfaults, but ...
3
votes
1answer
908 views

Chinese characters instead of Latin being written to file

When I run sed like this and print to a console everything is fine: sed '/Q/{ s/Q//g r /Users/ericbrotto/Desktop/question.txt }' Commision.txt But when I do this and output t a file: sed '/Q/{ ...
5
votes
4answers
2k views

Selinux is denying access to mysqld

I have a script that dumps a mysql database. It then compresses the file and this gets stored in my home folder by using cron. The problem is I seem to be getting an error message. mysqldump: ...
4
votes
3answers
3k views

Delete files based on year

I need to delete all files in a directory that were created in 2009. What command can I use to do that?
0
votes
3answers
260 views

Bash programing. The difference between double-clicking a program and running the program under console

I wrote a script named vpn.sh.The contents is as follows: #!/bin/sh cd /etc/openvpn sudo openvpn client.ovpn & when I am in konsole, ./vpn.sh runs well. But when I double click the vpn.sh ...
20
votes
4answers
4k views

Process substitution and pipe

I was wondering how to understand the following: Piping the stdout of a command into the stdin of another is a powerful technique. But, what if you need to pipe the stdout of multiple ...
6
votes
3answers
284 views

Shell and applications

Is it true that all commands that can run in bash are not actually part of bash? I'm gradually realizing I have been confusing the shell and the applications that can run in it.
4
votes
8answers
273 views

“which” with a little “grep”-like solution?

# which mkdir /bin/mkdir # which mkdi # How can I get the path of the e.g.: mkdir's binary without knowing the name of the binary file? (command). So that which mkdi would output the /bin/mkdir ...
2
votes
3answers
777 views

regexp in ksh for extensions tgz, tar.tgz

I'm trying to get a regexp (in ksh) to identify files with only the following extensions: tgz, tar.gz, TGZ and TAR.GZ. I tried several but can't get them to work. I'm using this regexp to select only ...
6
votes
1answer
3k views

Why does redirection (>) not work sometimes but appending (>>) does?

While studying for the RHCE, I came across a situation where stdin redirection does not work in bash: # file /tmp/users.txt /tmp/users.txt: cannot open `/tmp/users.txt' (No such file or directory) ...
1
vote
1answer
550 views

Good “progress bar” about md5sum checking progress?

I'm using this right now: time md5sum -c *.txt | pv | grep -v ': OK$' but aren't there any smart solutions that can list that how many files haven't been checked? I mean I have many md5sum's in ...
5
votes
3answers
1k views

How to wget Youtube horrible URL

I'm going to wget youtube search page where the URL is horrible. This is example when searching searchkeyword sorted by upload date: wget ...
6
votes
3answers
3k views

How to get file descriptor other than stdin stdout and stderr (to do something like $ program 1>file_1 3>file_2)?

When an executable produces an output I prefer to let the executable print the output to stdout in order to redirect them in a file as well to pipe them to another command. Let suppose that an ...
2
votes
3answers
7k views

What is the default shell for .sh in AIX?

I am fairly new to AIX machine. We would like to deploy some program into the AIX machine which is yet to come. We have a short experience in AIX machine and after login using putty, we felt the ...
2
votes
4answers
1k views

Shell scripts Linux -> Solaris conversion guide

I've developed a few Bash scripts on a LFS system which should now be made to work on a minimal installation of Sun Solaris 10. Is there a guide somewhere with at least some general tips for ...
2
votes
3answers
413 views

Source (.) piped curl output

I have a file, f, on my webserver with the following contents: alias ll='ls -l' I would like to (from another linux box) do the following, but I can't get the command right: curl http://myserver/f ...
26
votes
7answers
41k views

How can I get the size of a file in a bash script?

How can I get the size of a file in a bash script? How do I assign this to a bash variable so I can use it later?
9
votes
3answers
714 views

Why does the “she-bang” begin with a “#!”?

Why does the "she-bang" begin with a #!, like #!/bin/bash? I have always accepted that this how it is done, but is there a reason behind it? Why start with #; isn't that usually a comment? Or is it ...
2
votes
3answers
622 views

wget batch linux file

I am trying to download images from a manufacturer's site using wget. When I run the command from the shell it works fine. But when I run it from a file I am getting a placeholder file. Here is the ...
5
votes
3answers
172 views

How can I run a command for a list of packages?

I tried to install Gnome 3 on Debian Testing following this explanation. However, this didn't work and left me without any graphical user interface. At the moment I try to fix that and I realised ...
2
votes
2answers
129 views

In-place substitution for lines matching some pattern in a given set of files

Following on from my previous question: Remove slashes/parent paths from filenames inside CSS and Javascript content I arrived at the following command which replaces any filenames in these ...
3
votes
2answers
735 views

Remove slashes/parent paths from filenames inside CSS and Javascript content

I need to go through all my css and js files and if there is a filename referenced that has any slashes (/) at all then the slash should be removed. What I want is: if any files referenced are ...
4
votes
1answer
966 views

shopt -s nocaseglob is not working on Ubuntu

Case insensitive file name globbing is not working in bash on Ubuntu 11.04 64bit. The shell options specified in .bashrc are as follows: shopt -s nocaseglob shopt -s nocasematch shopt also shows ...
6
votes
2answers
1k views

redirection and pipeline

I was wondering about differences and relation between redirection and pipeline. Is pipeline only used to connect stdout output of a command to stdin input of another command? Is redirection only ...
6
votes
2answers
124 views

understand a sequence of redirections

If several redirections are used together, does changing their order make difference? How shall one understand the meaning of their order? Is the chained channel of redirections built as reading the ...
23
votes
4answers
26k 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 ...
1
vote
2answers
259 views

Weird executabe behaviour

I have a server machine with ubuntu 9.10. I am trying to put in place an executable, which turns out to be the latest flashplayer (debugger version). Somehow the file appears as present and ...
4
votes
3answers
472 views

General specification for command line interface

I was wondering where I can find and learn some general idea about the command line interface used in Linux and bash? As to now, I have found pieces of such information only from experience, such as ...
-1
votes
3answers
604 views

calling functions within a function

I need to fetch the results of different time ranges and email the results, but i am having trouble with the email part of the script, how can i send an email with both results? (15min range and ...
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 ...
3
votes
3answers
1k views

Is there a tr for translating into longer strings?

tr is great for translating a set of characters to another set of characters. Sometimes, I want to translate a set of characters to a set of strings, e.g. all < and > to &lt; and &gt;. ...
6
votes
3answers
393 views

Why might tmux only be capable of attaching once per shell session?

I'm using tmux on a Fedora 8 server (workplace restriction) to monitor several boxes on a stress rack. I noticed that I can only attach to my detached tmux session once per shell session. In order ...
7
votes
3answers
9k views

What is IFS in context of for looping?

I'm learning bash scripting right now. I was reading this thread: How to loop over the lines of a file? What is IFS? With for and IFS:
4
votes
4answers
156 views

Make mistakenly thinks rule succeeded because of 0-sized file generated by output redirect

In a makefile, I have several rules that look like this: out.txt: foo.sh input.txt ./foo.sh -i input.txt > out.txt If foo.sh fails, then out.txt will be created as a 0-sized file. If I run ...
17
votes
3answers
8k views

Bash: double equals vs -eq

I am doing integer comparison in bash (trying to see if the user is running as root), and I found two different ways of doing it: Double equals: if [ $UID == 0 ] then fi -eq if [ $UID -eq 0 ] ...
2
votes
3answers
4k views

grepping a variable and adding 1 to it

I have a variable containing a leading zeroes number, and I want to grep this variable and that same variable plus one. I made several attempts but ran into errors. Here's what I want to do: read var ...
12
votes
4answers
1k views

How did they manage to drive a Unix computer before mice and copy & paste?

Since Unix is 40 years old, Unix is older than the invention of the computer mouse. (actually only 3 years if Unix is from 1969 and the mouse from 1972) How in the world did a new user do anything ...
4
votes
3answers
313 views

Why do you need the “./” when executing programs in the current directory? [duplicate]

Possible Duplicate: Why do we use “./” to execute a file? It seems redundant and gets annoying after a while -- is there a way to change this? If not, can somebody explain the ...
4
votes
2answers
207 views

Why first set a variable and then export it instead of setting and exporting in one command?

If gpg-agent is executed, it outputs data that can be processed by a shell directly, e.g.: SSH_AUTH_SOCK=/tmp/ssh-apeOFqMF3292/agent.3292; export SSH_AUTH_SOCK; SSH_AGENT_PID=3293; export ...
6
votes
2answers
4k views

Howto create a permanent client connection with netcat?

I'm writing a bash script that constantly read a folder in a loop to send data to a server at a defined time interval. I'm using netcat as the tool to connect to the server and send the data. My ...
3
votes
1answer
491 views

Writing a bash script for apache conf files

I'm trying to automate creating vhosts on my computer. This is merely a learning experience for bash scripting. I'm currently novice. I'm trying to learn more about awk, sed. No, this isn't homework. ...
3
votes
3answers
3k views

Pass the background flag (&) through expect and ssh

My command line/bash fu is extremely weak, but I'm trying to hone my abilities. Hopefully someone can help. I wrote a super simple expect script so that I can SSH in to a headless box we're using at ...
8
votes
5answers
717 views

IO redirection and the head command

I was trying to quickly edit an .hgignore file from the Cygwin bash shell today, and I added a line that was a mistake. I'm not sure if this was the best way to do it, but I quickly thought of using ...
9
votes
1answer
1k views

confirmed exit using trap

I am trying to trap the Ctrl+C signal asking a confirmation from the user. The trapping part works fine. But once the signal gets trapped, it does not return to the normal execution. Instead, it quits ...