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32 Answered Questions for the topic shell

Shell Linux Bash


./configure : /bin/sh^M : bad interpreter?

I've been trying to install lpng142 on my fed 12 system. Seems like a problem to me. I get this error [root@localhost lpng142]# ./configure bash: ./configure: /bin/sh^M: bad interpreter: No such... more
Shell Linux Bash


How do I test if a variable is a number in Bash?

I just can't figure out how do I make sure an argument passed to my script is a number or not. All I want to do is something like this: test *isnumber* $1 && VAR=$1 || echo "need a... more
Shell Linux Bash


Defining a variable with or without export?

What is `export` for? What is the difference between: export name=value and name=value
Shell Linux


How can I recursively find all files in current and subfolders based on wildcard matching?

How can I recursively find all files in current and subfolders based on wildcard matching?
Shell Linux


Why doesn't "cd" work in a shell script?

I'm trying to write a small script to change the current directory to my project directory: #!/bin/bash cd /home/tree/projects/java I saved this file as proj, added execute permission with... more
Shell Linux Ubuntu


How to append one file to another in Ubuntu Linux?

I have two files: `file1` and `file2`. How do I append the contents of `file2` to `file1` so that contents of `file1` persist the process?
Shell Linux Process


What's the best way to send a signal to all members of a process group?

I want to kill a whole process tree. What is the best way to do this using any common scripting languages? I am looking for a simple solution.
Shell Linux Bash


What does set -e mean in a bash script?

I'm studying the content of this **preinst** file that the script executes before that package is unpacked from its Debian archive (.deb) file. The script has the following code: #!/bin/bash ... more
Shell Linux Bash


Get program execution time in the shell?

I want to execute something in a linux shell under a few different conditions, and be able to output the execution time of each execution. I know I could write a perl or python script that would... more
Shell Python Command


Calling an external command in Python?

How can I call an external command (as if I'd typed it at the Unix shell or Windows command prompt) from within a Python script?
Shell Linux Tar


Shell command to tar directory excluding certain files/folders?

Is there a simple shell command/script that supports excluding certain files/folders from being archived? I have a directory that need to be archived with a sub directory that has a number of very... more
Shell Unix Vim


Delete newline in Vim?

Is there a way to delete the newline at the end of a line in Vim, so that the next line is appended to the current line? For example: Evaluator<T>(): _bestPos(){ } I'd like to put this... more
Shell Linux Unix


Given two directory trees, how can I find out which files differ?

If I want find the differences between two directory trees, I usually just execute: diff -r dir1/ dir2/ This outputs exactly what the differences are between corresponding files. I'm interested... more
Shell Linux Find


How to exclude a directory in find . command?

I'm trying to run a `find` command for all JavaScript files, but how do I exclude a specific directory? Here is the `find` code we're using. for file in $(find . -name '*.js') do java -jar... more
Shell Unix Bash


How to represent multiple conditions in a shell if statement?

I want to represent multiple conditions like this: if [ ( $g -eq 1 -a "$c" = "123" ) -o ( $g -eq 2 -a "$c" = "456" ) ] then echo abc; else echo efg; fi but when I execute the script,... more
Shell Unix Arrays


Loop through an array of strings in Bash?

I want to write a script that loops through 15 strings (array possibly?) Is that possible? Something like: for databaseName in listOfNames then # Do something end
Shell Linux Unix


How to assign name for a screen?

I'm using the `screen` multiplexer tool on the command shell and open a lot of screens. I then forget which process ID associates with which task. I would like to set a name for a screen but can't... more


How to determine whether a given Linux is 32 bit or 64 bit?

When I type `uname -a`, it gives the following output. Linux mars 2.6.9-67.0.15.ELsmp #1 SMP Tue Apr 22 13:50:33 EDT 2008 i686 i686 i386 GNU/Linux How can I know from this that the given OS is... more
Shell Unix Sh


How to read a file into a variable in shell?

I want to read a file and save it in variable, but I need to keep the variable and not just print out the file. How can I do this? I have written this script but it isn't quite what I needed: ... more


How can I reverse the order of lines in a file?

I'd like to reverse the order of lines in a text file (or stdin), preserving the contents of each line. So, i.e., starting with: foo bar baz I'd like to end up with baz bar foo Is there... more


How do I prompt for Yes/No/Cancel input in a Linux shell script?

I want to pause input in a shell script, and prompt the user for choices. The standard 'Yes, No, or Cancel' type question. How do I accomplish this in a typical bash prompt?


How do I know the script file name in a Bash script?

How can I determine the name of the Bash script file inside the script itself? Like if my script is in file ``, then how would I make it to display "You are running" message... more
Shell Linux Unix


Aborting a shell script if any command returns a non-zero value?

I have a Bash shell script that invokes a number of commands. I would like to have the shell script automatically exit with a return value of 1 if any of the commands return a non-zero value. Is... more
Shell Unix Bash


Bash tool to get nth line from a file?

Is there a "canonical" way of doing that? I've been using `head -n | tail -1` which does the trick, but I've been wondering if there's a Bash tool that specifically extracts a line (or a range of... more
Shell Linux Bash


How to 'grep' a continuous stream?

Is that possible to use `grep` on a continuous stream? What I mean is sort of a `tail -f <file>` command, but with `grep` on the output in order to keep only the lines that interest... more

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