The shell is unix's command-line interface. You can type commands in a shell interactively, or write scripts to automate tasks.

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2
votes
1answer
30 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
113 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
10 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 $* ...
24
votes
4answers
3k 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 ...
3
votes
2answers
347 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 ...
4
votes
2answers
66 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 ...
6
votes
3answers
469 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
62 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
3answers
81 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 ...
2
votes
7answers
70 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
35 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
74 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 ...
3
votes
3answers
74 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 ...
4
votes
3answers
193 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
60 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 ...
0
votes
4answers
55 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 ...
2
votes
1answer
133 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
52 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
97 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 ...
8
votes
3answers
1k 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.
3
votes
3answers
83 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: ...
2
votes
1answer
75 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 ...
6
votes
2answers
145 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 ...
3
votes
3answers
124 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
44 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
31 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
75 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 ...
1
vote
3answers
38 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
33 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 ...
2
votes
1answer
49 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
51 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 ...
0
votes
2answers
54 views

why is ! character used in shell scripts [duplicate]

I recently encountered a situation where I tried to use ! as a record separator for my string array in shell script. When I used it in my shell script, the script got expanded automatically. An ...
-2
votes
1answer
59 views

concatenate or remove multiple files of a directory

In general for file concatenation with the same extension, we use cat *.txt. But in case we are in a different directory and trying to concatenate another directory's files how to do that ? I have ...
2
votes
3answers
45 views

A shell tool to “tablify” input data containing ANSI escape codes

I have input containing ANSI color codes that I'd like to tablify. I want the output to remain colored, so the tablified output should maintain the ANSI color codes. Hence, naively stripping them away ...
1
vote
1answer
54 views

Why does redirection in crontab result in a zero byte file?

System: Xubuntu 13.10 When I have this crontab entry */5 * * * * cat /home/dbk/.bash_aliases &> /home/dbk/Desktop/junk junk has a byte size of 0. Running $ cat /home/dbk/.bash_aliases ...
11
votes
4answers
1k views

How Does Linux deal with shell scripts?

For this question, let's consider a bash shell script, though this question must be applicable to all types of shell script. When someone executes a shell script, does Linux load all the script at ...
1
vote
0answers
25 views

How to automatically launch a lxc container on ssh connection?

I'm attempting to setup a system that automatically creates a new sandbox on a ssh login to use as a temporary jump box into my server. So to do this I was wonder how to setup lxc to spin up a new ...
5
votes
4answers
169 views

Run a command when system is idle and when is active again

I want to run a command when the user becomes inactive (the system is idle). For example: echo "You started to be inactive." Also, when the user becomes active again (the system is not idle ...
1
vote
1answer
56 views

Not able to copy multiple files using rsync 3.0.9 version?

I am trying to copy two files using rsync from a machineB but somehow it always copies only one file but not the second file - Here is the syntax I am using - rsync -avz ...
4
votes
2answers
227 views

Merge fields in a file

I have a file with 7 columns, a GFF file having chromosomal regions.I want to collapse the rows where REGION ="exon" to only one row in the file.The row has to be collapsed on the basis of regions ...
2
votes
2answers
28 views

Setting tabstop for bash output

Is it possible to set a tabstop (number of spaces per tab) for the more and less commands? In vi, I've added this line to .vimrc set tabstop=4 However when I read through a file with more it still ...
4
votes
2answers
92 views

Find command returns wrong files

I'm trying to find files in a folder using find command which are a day older than the day on which the command is run.. I use the following command: FILES_dcn=($(find $dir_dcn -maxdepth 1 -type f ...
4
votes
4answers
165 views

Pass shell variable as a /pattern/ to awk

Having the following in one of my shell functions: function _process () { awk -v l="$line" ' BEGIN {p=0} /'"$1"'/ {p=1} END{ if(p) print l >> "outfile.txt" } ' } , so when called as ...
4
votes
6answers
130 views

List all binaries from $PATH

Is there one-liner that will list all executables from $PATH in bash.
5
votes
1answer
112 views

understanding the default value of IFS

In my GNU bash version 4.2.8, IFS has a default value of space, tab and line feed by default: usr@T42 ~ $ echo -n "$IFS" | hexdump -C 00000000 20 09 0a | ..| ...
1
vote
3answers
124 views

Delete files with same name at the end of the file

Delete files with same name at the end of the file i have a lot of files in my folder and sub directories like ajax_hostel_room_master.php.php class_hostel_registration.php.php ...
2
votes
3answers
150 views

How to use rsync or scp to efficiently copy the files from machineB and machineC to machineA?

I am running my shell script on machineA which copies the files from machineB and machineC to machineA. If the file is not there in machineB, then it should be there in machineC for sure. So I will ...
3
votes
1answer
86 views

What does exec 3<&1 do?

I understand exec can do I/O Redirection on current shell level. but I only sees usage like exec 6<&0 # Link file descriptor #6 with stdin. # Saves stdin. exec 6>&1 # ...
1
vote
2answers
78 views

How to find out all the files in other machines using bash shell script?

I am trying to find out which files are in machineB and which files are in machineC. And I need to run my shell script on machineA to figure out which files are in machineB and which files are in ...
8
votes
3answers
203 views

How to execute a command repeatedly with different arguments?

I'm on Ubuntu. I copied some arguments (separated by newline) and I can use xsel to print them out like this $ xsel arg1 arg2 arg3 arg4 ... Now, I want to use each of these arguments for another ...