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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1answer
238 views

Installation of latest version R for linux

First I typed sudo gedit /etc/apt/sources.list after that I got one sources list then I typed deb http://cran.rstudio.com/bin/linux/debian wheezy-cran3/ then I get the error like this No ...
25
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15answers
3k views

What customizations have you done on your shell profile to increase productivity?

I know some people have some startup scripts and some people personalise the prompt. One developer uses short aliases for the long path he often visits and the frequent commands he runs. What are all ...
84
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4answers
2k views

Can I somehow add a “&& prog2” to an already running prog1?

Most shells provide functions like && and ; to chain the execution of commands in certain ways. But what if a command is already running, can I still somehow add another command to be executed ...
61
votes
6answers
104k views

How to monitor CPU/memory usage of a single process?

I would like to monitor one process's memory / cpu usage in real time. Similar to top but targeted at only one process, preferably with a history graph of some sort.
39
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2answers
76k views

How can I execute local script on remote machine and include arguments?

I have written a script that runs fine when executed locally: ./sysMole -time Aug 18 18 The arguments "-time", "Aug", "18", and "18" are successfully passed on to the script. Now, this script is ...
59
votes
3answers
34k views

Find out current working directory of a running process?

What command(s) can one use to find out the current working directory (CWD) of a running process? These would be commands you could use externally from the process.
29
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3answers
21k views

What does ${1+“$@”} mean in a shell script, and how does it differ from “$@”?

In the Perl documentation, perlrun(1) suggests launching Perl scripts using a bilingual shell/Perl header: #!/bin/sh #! -*-perl-*- eval 'exec perl -x -wS $0 ${1+"$@"}' if 0; What does ${1+"$@"} ...
49
votes
4answers
34k views

Clone ownership and permissions from another file?

Is there a command or flag to clone the user/group ownership and permissions on a file from another file? To make the perms and ownership exactly "like" that of another file?
36
votes
7answers
3k views

Is test or [ or [[ more portable both between bash shells and between other shells?

I see I can do $ [ -w /home/durrantm ] && echo "writable" writable or $ test -w /home/durrantm && echo "writable" writable or $ [[ -w /home/durrantm ]] && echo "writable"...
36
votes
2answers
22k views

What does “3>&1 1>&2 2>&3” do in a script?

I saw this line in a script: DEVICE=`dialog --inputbox "Festplatten-Laufzeit auslesen. Gebe Sie das gewünschte Device an: " 0 70 "" 3>&1 1>&2 2>&3` What is 3>&1 1>&...
33
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6answers
15k views

How to check if bash can print colors

I want to know if there's any way to check if my program can output terminal output using colors or not. Running commands like less and looking at the output from a program that outputs using colors,...
26
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1answer
639 views

A shell tool to “tablify” input data

A long time ago I remember using a command that makes its input into a nicely formatted table. For example, for this input, apple 1 100 orange 20 19 pineapple 1000 87 avocado 4 30 The output will ...
11
votes
2answers
14k views

How can you log every command typed

How can you log every command someone has entered into the shell? I'm asking on both the basis of protecting yourself if you are logged into someone else's server and something breaks, or if someone ...
23
votes
2answers
9k views

What is meant by a shell is in “vi” mode or “emacs” mode?

This question follows directly from the answer. In this case I am specifically unable to understand the part which says: In that regard, its behaviour is closer to emacs' than with bash(readline)...
16
votes
3answers
11k views

When do you need 'nohup' if you're already forking using '&'?

First this question is related but definitely not the same as this very nice question: Difference between nohup, disown and & I want to understand something: when I do '&', I'm forking right?...
15
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1answer
12k views

How do you use output redirection in combination with here-documents and cat?

Let's say I have a script that I want to pipe to another command or redirect to a file (piping to sh for the examples). Assume that I'm using bash. I could do it using echo: echo "touch somefile ...
16
votes
3answers
3k views

How to delete part of a path in an interactive shell?

Is there a shortcut in bash and zsh to delete one component of a path? For example, if I type ls ~/local/color/, and the cursor is at the end of line, is there a shortcut to delete the color/ at the ...
32
votes
3answers
72k 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" DESTINATION="/home/...
23
votes
4answers
12k views

Save complete GNU screen session state

Is it possible to persist the "state" of a GNU screen window (or just a standard shell) so that I can reload everything after a reboot: The number of opened shells The name of each shell The current ...
18
votes
4answers
17k views

How to parse hundred html source code files in shell?

I have a couple of hundred html source code files. I need to extract the contents of a particular <div> element from each of these file so I'm going to write a script to loop through each file. ...
17
votes
1answer
11k views

what do you mean by interactive shell?

UNIX: The Complete Reference, Second Edition by Kenneth H. Rosen et al. You can start another shell after you log in by using the name of the shell as a command; for example, to start the ...
16
votes
9answers
30k views

How to compare to floating point number in a shell script

I want to compare two floating point numbers in a shell script. The following code is not working: #!/bin/bash min=12.45 val=10.35 if (( $val < $min )) ; then min=$val fi echo $min
12
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7answers
45k views

Which shell should I use - tcsh vs bash? [closed]

I have been using tcsh for a long time now. But whenever I am searching for something, I often find that the methods specified are bash specific. Even the syntax for the shell scripts is different for ...
9
votes
3answers
43k views

How to merge two files based on the matching of two columns?

I have file1 likes: 0 AFFX-SNP-000541 NA 0 AFFX-SNP-002255 NA 1 rs12103 0.6401 1 rs12103_1247494 0.696 1 rs12142199 0.7672 And a file2: 0 AFFX-SNP-000541 1 0 ...
20
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4answers
6k views

What happens if you edit a script during execution?

I have a general question, which might be a result of misunderstanding of how processes are handled in Linux. For my purposes I am going to define a 'script' as a snippet of bash code saved to a text ...
19
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3answers
7k views

Rule for invoking subshell in Bash?

I seem to misunderstand the Bash rule for creating a subshell. I thought parentheses always creates a subshell, which runs as its own process. However, this doesn't seem to be the case. In Code ...
23
votes
3answers
9k 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 ...
23
votes
4answers
4k views

How to know the “level” of shells I am in?

If I open a terminal like xterm I will have a shell. Then if I use ssh or zsh I will have another "level" of shell. Is there a way to know how many times I have to Ctrl+D or type exit to exit all of ...
18
votes
3answers
14k 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, ...
13
votes
3answers
13k views

What is the purpose of -e in sed command?

I can't find any documentation about the sed -e switch, for simple replace, do I need it? e.g. sed 's/foo/bar/' VS sed -e 's/foo/bar/'
12
votes
4answers
16k views

How do I reverse a for loop?

How do I properly do a for loop in reverse order? for f in /var/logs/foo*.log; do bar "$f" done I need a solution that doesn't break for funky characters in the file names.
9
votes
4answers
13k views

How do I change folder timestamps recursively to the newest file?

I was wondering if anyone knows how to change the timestamps of folders recursively based on the latest timestamp found of the files in that folder. So for example: jon@UbuntuPanther:/media/media/...
29
votes
4answers
4k views

What is the correct name for the “>” command

I was trying to find how to pass some text to a file without overwriting what's there already using the > command and I realised I don't know what it's called. Searching for right arrow or right ...
27
votes
4answers
22k views

How to Execute multiple command using nohup

I need to execute multiple commands using nohup. Each command should be executed after the previous command. I used this command as an example: nohup wget $url && wget $url2 > /dev/null ...
24
votes
3answers
14k views

bash multi line command with comments after the continuation character

Consider echo \ # this is a comment foo This gives: $ sh foo.sh # this is a comment foo.sh: line 2: foo: command not found After some searching on the web, I found a solution by DigitalRoss on ...
17
votes
2answers
5k views

How to apply recursively chmod directories without affecting files?

After I apply chmod -R to a directory, permissions are changed for everything within (files and directories). How can I add execute/search (x) permissions to directories without modifying the files?
10
votes
5answers
11k views

How do I perform an action on all files with a specific extension in subfolders in an elegant way?

My current best bet is: for i in $(find . -name *.jpg); do echo $i; done Problem: does not handle spaces in filenames. Note: I would also love a graphical way of doing this, such as the "tree" ...
15
votes
2answers
2k views

Why does using `yes` on bash pipelines *not* cause infinite loops?

According to its documentation, bash waits until all commands in a pipeline have finished running before continuing The shell waits for all commands in the pipeline to terminate before returning a ...
11
votes
3answers
3k views

Pasting from clipboard to vi-enabled zsh or bash shell

I'd like to be able to paste from the system clipboard (or text selection) into my "vi-like" shell prompt using the keyboard. I normally use zsh and sometimes bash. In both cases, I have the shell set ...
10
votes
1answer
797 views

Is it possible to use `find -exec sh -c` safely?

I'm trying to use find to echo 0 into some files, but apparently this only works with sh -c: find /proc/sys/net/ipv6 -name accept_ra -exec sh -c 'echo 0 > {}' \; But using sh -c with find -exec ...
3
votes
6answers
2k views

When does a shell get executed during the linux startup process

I do not understand when does a shell, lets say bash, get executed, which program runs bash initially first.
3
votes
1answer
3k views

pass 1 environment variable using sudo

Is this a correct way for passing an environment variable in sudo ? sudo -u www-data -b env FOOBAR="foobar" /home/user/folder/daemon
22
votes
5answers
8k 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 ...
11
votes
6answers
21k views

How to remove blank lines from a file in shell?

I want to remove all empty lines from a file. Even if the line contains spaces or tabs it should also be removed.
9
votes
1answer
287 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 ...
6
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3answers
938 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 ...
3
votes
1answer
947 views

What's the conf file reading between login and non-login shell?

I found that those are .bash_profile, .bashrc, .bash_login, .profile. What's the reading sequence between them?
12
votes
4answers
41k 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=` ...
10
votes
3answers
22k views

Automating textual input from a bash script without using EOF

I'm running Ubuntu Linux. Suppose there is a program called myprogram. This program prompts the user for input; specifically, the user must type an integer when prompted and press Enter. I would ...
7
votes
7answers
1k views

Command line tool to “cat” pairwise expansion of all rows in a file

Suppose I have a file (call it sample.txt) that looks like this: Row1,10 Row2,20 Row3,30 Row4,40 I want to be able to work on a stream from this file that is essentially the pairwise combination of ...