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
250 views

Merging text files based on their filename

I have hundred of files with the following format: 2013_01_19_xyxyxyx.txt 2013_01_19_xyxyxyx.txt 2014_03_21_xyxyxyx.txt 2014_03_21_zxzxzxz.txt 2014_03_22_abababa.txt 2014_03_22_cbcbcbc.txt etc. I ...
1
vote
1answer
213 views

Execute commands on tmux detach

Is it possible to execute commands on tmux detach? I usually have a rails console and server running in the tmux session, on detach is it possible to automatically end those?
1
vote
1answer
344 views

`tar` with `find` with removing original file extension

I want to create tb2 files from bunch of text files like this. tar cfj $(basename ./2014_04_09.txt .txt).tb2 $(basename ./2014_04_09.txt) With this command I can create a archive file 2014_04_09.tb2 ...
106
votes
3answers
11k views

Why is “echo” so much faster than “touch”?

I'm trying to update the timestamp to the current time on all of the xml files in my directory (recursively). I'm using Mac OSX 10.8.5. On about 300,000 files, the following echo command takes 10 ...
12
votes
5answers
975 views

copy smallest files first?

I have a large directory containing subdirectories and files that I wish to copy recursively. Is there any way to tell cp that it should perform the copy operation in order of file size, so that the ...
17
votes
6answers
2k views

Why do I have to cd out of a deleted directory?

On my server I have a directory structure looking something like this: /myproject/code I normally have an ssh connection to the server and 'stand' in that directory: root@machine:/myproject/code# ...
2
votes
1answer
588 views

What is the ` character or symbol called and what is its significance outside of SE code formatting? [duplicate]

What is the ` character's name and what is its significance outside of SE code formatting because I cannot get it to work? I'm familiar with its use in the Stack Exchange forums used to format code ...
2
votes
4answers
218 views

Can a running script identify the logging context?

Let us say I redirect the STDOUT, STDERR of a program to files. ./script.sh 1> output.log 2> error.log Can the running program find this out i.e. know the paths to these files?
4
votes
1answer
3k views

How to trace system calls being invoked after typing command?

This question is relevant to the question of 'what happens when we type a simple command on shell?' I posted earlier. (I thought it would be better to post it seperately. But if not, please let me ...
21
votes
2answers
4k views

What happens when we type a simple command on shell? [duplicate]

I have a simple doubt on execution of a simple command. As per my understanding, when we type a command such as ls on interactive shell, Shell interpretes the command. Shell creates a child process ...
22
votes
2answers
40k views

Why is my find not recursive?

I am running the following command, but it is not performed recursively: find . -name *.java I know there are java files further down in the current directory but it is performing the find on the ...
5
votes
3answers
7k views

Close all file descriptors in bash

Is there a way to close all the open file descriptors, without having an explicit list of them beforehand?
1
vote
2answers
103 views

command condition sometimes integer sometimes string

I want to execute this condition while [ $(cat /path_of a file/) -eq 1 ] The condition is only correct if $(cat /path_of a file/) is an integer and not a string ! How can I overcome this ...
6
votes
3answers
915 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 ...
10
votes
4answers
5k views

/bin /etc /lib64 /root /sbin deleted or moved by mv folder/* /* while su

OS is Centos 6.5 64-bit I downloaded a tar file and wanted to untar and mv it. I untared, then accidentally (as root) ran mv folder/* /* instead of mv folder/* . bash said it couldn't overwrite some ...
3
votes
1answer
9k views

Bash command not found error

Why would the following script give following errors : ./check1.sh: line 10: Hi,: command not found ./check1.sh: line 21: syntax error: unexpected end of file check1.sh: #!/bin/bash subj="host ...
1
vote
1answer
115 views

Is there an advantage in using ksh over zsh? [closed]

Or are there any advantages for using ksh over zsh? Would any specific commands not execute successfully across the shells or are the major differences not command related, but something else?
2
votes
2answers
957 views

Linux Shell fundamentals: How can I check the file descriptors status, (where are redirected to) right now without lsof?

I am learning about file descriptors for the case of Linux, and I was wondering if there is any command showing a complete list that allows me to know where is each one redirected to in this moment. ...
3
votes
2answers
2k views

Passing arguments to su-provided shell

man su says: You can use the -- argument to separate su options from the arguments supplied to the shell. man bash says: -- A -- signals the end of options and disables further option ...
3
votes
1answer
390 views

Accidentally typed crontab with just the dash

What happens when I type just "crontab -"? The "e" didn't take before I hit Enter. It just moved the cursor to the next line and I had to Ctrl+C to exit, but I'm not sure what it did exactly. I'm on ...
8
votes
2answers
612 views

How do I elevate privileges in the middle of pipeline?

My guess was as follows: echo "Generating some text" | su - -c cat >/output/file But su says: su: must be run from a terminal What would you do?
1
vote
2answers
49 views

Install-on-Demand Wrapper Function for Executables

How do I make the following function work correctly # Install git on demand function git() { if ! type git &> /dev/null; then sudo $APT install git; fi git $*; } by making git $* ...
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 ...
4
votes
2answers
617 views

Interpret backspaces in file

Is there a way to interpret/"execute" backspaces in a file/line using common bash commands? I have a console program which prints some stuff and than erases it using backspaces and finally writes the ...
5
votes
2answers
209 views

Command substitution vs I/O Redirection?

I am wondered about differences between I/O Redirection and Command substitution? For example when I want to redirect which command output to cd command (I know that it's not a directory) then the ...
7
votes
3answers
522 views

What is the difference between the use of ; and executing a script

I'm using bash as my main shell, but it's an open question and responses for shells others than bash are very welcome. If I'm typing interactively #original line #wget http://something.com &...
1
vote
3answers
2k views

`wait` doesn't wait for `wget --background`

I have gone through several SE posts on the unix wait command and none of the posts resolve my problem. I have a weather forecast model to run. It has first to prepare some folders, then download data ...
2
votes
2answers
637 views

Redirecting only stderr to a pipe

This code snippet is from Advanced Bash Scripting Guide. # Redirecting only stderr to a pipe. exec 3>&1 # Save current "value" of stdout. ls -l 2>&1 >&...
5
votes
7answers
9k views

Sort the files in the directory recursively based on last modified date

Sort the files in the directory recursively based on last modified date I have modified a lot of files in my directory want to know what are those files by sorting them by the last modified date ...
0
votes
1answer
594 views

How to pass a flag from one script to a function in another script

I have a script that installs a bunch of programs (homebrew, git, etc) and I have it log to stdout all the things that its doing along the way, but I want the ability to pass a flag, such as --no-log ...
1
vote
2answers
671 views

Union of two files and unique in new file

I have two files with few similar column one, two and third column with small variation and few other columns as follows. file 1: AT1 AT22 24 1 ATAGATA ATTATAT AT2 AT24 22 0 ATAGATA ATTATAT ...
8
votes
4answers
14k views

Bash, how to let some background processes run but wait for others?

I have (yet) another wait, &, && control flow question.. Say I have a script something like this where I want to do as much work at the same time as possible: # may take some hours ...
11
votes
3answers
21k views

Execute a command on user logon

In Linux desktop system, I want to execute a command when the user logs in. After reading some other posts, I tried to insert the command in ~/.bashrc but unsuccessfully. Moreover, the system uses a ...
0
votes
1answer
70 views

Scripting - Folders with spaces

I'm trying to write a script that's robust enough to work with spaces. Its currently in a for loop, but the problem I'm having is folders with spaces in its name. ASOURCE="Home Photos 2012 camcorder"...
1
vote
5answers
3k views

bash event not found trying to match and exclude parenthesis in grep

In a very long line I'll summarize with: (foo),(bar,baz(word,right),(end) I want to print only: (bar,baz(word,right To match the second parenthesis, I exclude the word that follows the ...
14
votes
1answer
45k views

Sort data in descending order of first column, for equal values, use second column in ascending order

Allow me to clarify: Assume I have some keywords with frequency of their usage: 12 Hi 7 Hash 7 C++ 9 Superuser 17 Stackoverflow 9 LaTeX 42 Life 9 Ubuntu What I want, is to sort this data ...
1
vote
1answer
224 views

List files, directories and executables in current directory

I have php shell and I have function that do just that (but it give me error when I call scandir($path) function because of restriction in php), so I need to use my bash shell to do the same. It can ...
1
vote
1answer
468 views

/etc/profile is not read in changed user shell

I need to run custom binary when user logged in to system ,so that I have changed user's shell to /bin/binary to /etc/passwd but I have observed that /etc/profile file was not read when I logged in ...
10
votes
3answers
43k views

What does $# mean in shell?

What does $# mean in shell? I have code such as if [ $# -eq 0 ] then I want to understand what $# means, but Google search is very bad for searching these kinds of things.
4
votes
3answers
1k views

What's the right way to set “dynamic” PATH in bash? (for android sdk)

I have android sdk installed, and I want the binaries in build-tools/android-VERSION to be available in PATH, so I add few lines: ANDROID_SDK=/Application/Binaries/adt-bundle-linux-x86_64-20140321/...
2
votes
1answer
1k views

remove duplicate files in 2 directories

I have two folders (w/ subfolders) containing files that both contain essentially the same content. Example: /folder/files/data/new /folder/files/data/old Is there way to delete all files in /new ...
7
votes
2answers
815 views

Can the shell be more “offensive”?

My Gentoo Linux is compiled with the offensive USE flag enabled: # sudo su - Password: Hold it up to the light --- not a brain in sight! Password: It is also possible to select fortunes based on ...
4
votes
3answers
697 views

how do I do this: dd if=coolstuff.iso of=(ssh kev@mypi )

the card reader on my laptop doesn't want to work. can I use dd (or some other tool) to write an image to a networked disk. I am trying to replace one raspberry pi distro with another. The SD card ...
1
vote
1answer
351 views

how to check if mysql table is used or an application accesses the table in shell script?

A shell script is doing dump for a mysql table, but before dumping the table I want to check if this table is used by any other application. If so, I want to wait and enter in a loop until the ...
2
votes
2answers
82 views

git diff - listen for key press

I want to run the following commands: git diff git commit git commit will open the default editor to edit the commit message. But if the difference if not too long it will close immediately. How ...
2
votes
3answers
571 views

Count result in a find/exec statement

I have some Perl files which I have to modify through a simple sed call. Basically, I have to remove the first line of all of them. Currently, I managed to do this : find <PATH> -type f -name "*...
6
votes
3answers
9k views

How to output comma-separated strings using bash brace expansion

I'd like $ echo a{b,c,d} to output a comma-separated list like ab,ac,ad instead of the usual output ab ac ad What's the easiest way to do that on the command line?
0
votes
1answer
500 views

Commands inside bash not being interpreted?

I'm trying to execute a command inside a bash script, $(pwd) is not being interpreted at all, and not even using eval. This do not work: cat apache-vhost.conf | sed 's/{path}/$(pwd)/g' Neither ...
3
votes
1answer
1k views

Where can I find a good boilerplate bashrc?

I've used unix/linux at work in the past, and recently started developing on a Mac. I'd always (lovingly) borrow co-workers' bashrc's for a good starting point, such as common aliasing and commands, ...
1
vote
1answer
91 views

Paradox about a-z vs A-Z

I wrote a shell script to recognize the type of character printf "Enter a character: " read var case "$var" in [a-z]) echo "You entered a lower case alphabet." ;; [A-Z]) echo "...