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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2answers
41 views

create file from function

#!/bin/bash # trims trailing spaces and tabs from file, using awk utility function remove_trail() { [ ! $# -lt 2 ] || { echo "Usage: $FUNCNAME file-to-trim out-file"; return 1; } # args ...
1
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4answers
52 views

Write program output to log file containing PID in its name

How can I start a program and write its output to a log file, where the log file contains the PID in its name? I tried program_a > log_$! which doesn't work since $! is the PID of the last ...
3
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3answers
185 views

Efficient way to create multiple files

I have been testing find directory which is taking max inodes and while testing I had run touch test_{1..1391803}.txt But it's give me error "-bash: /usr/bin/touch: Argument list too long", now ...
2
votes
1answer
63 views

How to detect global key presses

I have an Asus laptop that has a special key that can be configured to launch any software (at least on Windows). The general question is: how can I detect any key press (globally)? Then, how ...
0
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2answers
55 views

How to reset the file descriptor

I was trying to use file descriptor for printing the lines in the file #!/usr/bin/ksh exec 3<&0 exec 0< file.txt while read LINE do echo “$LINE” done and I am done with my code ,it ...
2
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4answers
91 views

What are SSH_TTY and SSH_CONNECTION?

What are the SSH_TTY and SSH_CONNECTION variables for? On my Ubuntu system both of them are blank; what values should they have?
1
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1answer
57 views

Single command to login to SSH and run program?

Is there a way to structure a single command to login via SSH to a remote server and run a program on the remote login shell? In the OpenSSH manual, it reads "If command is specified, it is executed ...
2
votes
2answers
106 views

grep and directories containing spaces

I would like to search all files containing an association of strings (here the files should contain 'arthur' AND ('déni' OR 'deni') for instance) in a directory and subdirectories. After some search ...
5
votes
1answer
167 views

When is it important to write portable scripts?

Most code I write is in PHP. I have recently started learning shell scripting. Most of the resources and tutorials that I've come across are specific to Bash. Some warn about bashisms and some don't. ...
1
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1answer
71 views

How to exit out of the shell script successfully so that python subprocess think it is successfull exit? [closed]

Below is my shell script which simply execute a url like this http://example.com:8080/beat and parse the response and verify certain conditions on it. If that condition is met, then exit successfully ...
1
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3answers
43 views

Executing bash shell scripts

I am reading an article on executing bash shell scripts. Method 1: Create a directory for your shell scripts and add the directory to the contents of the PATH variable, so that you can execute the ...
3
votes
4answers
186 views

find -exec exit 1 \; Doesn't work neither does find -exec sh -c exit 1 \;

Using Enterprise Linux 5/6, Bash 4.x I want this type of logic: # IF temp file exists, exit because we are restarting already find /tmp/restarting_server -mmin -10 -exec exit 1 lsof -i TCP:1234 ...
0
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4answers
172 views

Starting with bash: -lt and -gt arguments

I'm starting with bash and I found the following: if test $first -lt $second then echo $first is lower than $second else if test $first -gt $second then echo $first is higher than $second ...
0
votes
1answer
35 views

Updating last modified time of a file

I have created a script to read 15 pcap files from a folder and merge then into one file using mergecap command. I want the merged file to have the creation time same as the first file of the 15 files ...
5
votes
2answers
352 views

Making sure a command has executed in bash

I have a bash file with commands to merge pcap files. I want to know if there is anyway to make sure a line in bash runs or not. Like in windows bat file we have %ErrorLevel% ¨ Say a command touch -r ...
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votes
3answers
129 views

How to get IP Address using shell script? [duplicate]

Want to get the IP address using Shell script. Without knowing the eth0 or eth1 or eth2 How to get the particular IP address. I am not interest to get localhost address, want to get private IP ...
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votes
4answers
84 views

How to add a 3 lines in a file using shell script? [closed]

I have a file, that file contain 10 lines. And now I want to add 3 lines to end of the file using shell script. After add lines, If I run the script again I don't want to add same lines again. ...
1
vote
0answers
34 views

Logging into multiple SSH servers as root and create an user with same power as root does [closed]

I need a script from which I can log into multiple servers as root (but not all root passwords are same;there are 3-4 different root passwords) and make a superuser (user with same access as root) but ...
3
votes
3answers
47 views

Force shell command to return [closed]

I'm running a command (not part of the standard distro) that sometimes does not return the cursor. That is, I have to press enter myself. The issue is that if I want to do it from a C++ program, ...
7
votes
1answer
324 views

Is this redirecting to /dev/null?

I found this script on the arch wiki which prefixes an ffmpeg command like this < /dev/null ffmpeg -i "$a" -qscale:a 0 "${a[@]/%flac/mp3}" I understand the ffmpeg command, it is the < ...
1
vote
1answer
71 views

Command works with tilde at the end. How?

I'm on Ubuntu. I have a script called myscripts in /usr/bin/myscripts This script simply changes the current directory to ~/Work/MyScripts Normally, I simply open a terminal and type ~/Desktop$ . ...
1
vote
1answer
26 views

Pass login messages to tmux

When I login, I connect to a tmux session (either by exec'ing tmux if there is no current session, or exec'ing tmux attach if there is). However this means I don't see the login messages (/etc/issue, ...
4
votes
3answers
86 views

Search for specified keywords in files and copy to a new filename based on the keyword

I'm trying to create an .sh script where if any keyword is found in a file then copy that file to the directory /pathtofolder/keywords/$thefirstkeywordfound (overwrite the file if it already exists). ...
2
votes
2answers
43 views

What does `env COLUMNS=%S ps …` do?

I have seen the syntax env COLUMNS=%sin shell scripts, e.g. see the line below from the Helm package in Emacs: env COLUMNS=%s ps -axo pid,user,pri,nice,ucomm,tty,start,vsz,%%cpu,%%mem,etime,command ...
2
votes
1answer
87 views

How to find files that contain newline in filename?

I am trying to find files that have a newline in the filename. But I can't figure out what pattern to use. The following works, but is not very useful if I want to use it in indented code. find . ...
21
votes
4answers
1k views

Is the shell permitted to optimize out useless terminating commands?

If a shell is asked to perform a probably useless (or partially useless) command known to terminate, such as cat hugeregularfile.txt > /dev/null, can it skip that command's execution (or execute a ...
2
votes
2answers
42 views

In OS X Darwin, why can I interfere with text input across user sessions using cat?

OS X Darwin: Disrupting Terminal Sessions Across User Identities How, in Brief: with cat < /dev/ttys_, in Terminal. My Question This OS X 10.9.2 Darwin behaviour seems odd to me, and I would ...
1
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2answers
77 views

Running a bash script as root prevents asynchronous execution?

The script below get's executed differently if run as a root user. #!/bin/sh gnome-terminal -x sleep 10 echo 'Why must I wait for sleep to finish?' If its run as a regular user, message is ...
5
votes
4answers
143 views

Can a program next in a pipeline see the exit code of the previous program?

I would like to make a pipeline of Bash scripts like this prog1 | prog2 such that prog2 can see the exit code of prog1 and act differently based on that information. Is this possible?
1
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1answer
53 views

How do I rename lots of files on a directory without changing their extensions? [duplicate]

I have a problem! I have a bunch of image files with extensions. Jpg and. Png. I wrote a script that renames the files, changing their names in a pattern followed by a number like this: ... ...
16
votes
2answers
394 views

How can a bash script detect if it is running in the background?

Is there way for a bash script to know if it is running in the foreground or background, and so it can behave slightly differently in each case?
15
votes
2answers
321 views

Quoting within $(command substitution) in Bash

In my Bash environment I use variables containing spaces, and I use these variables within command substitution. Unfortunately I cannot find the answer on SE. What is the correct way to quote my ...
2
votes
2answers
105 views

Why does bash add single quotes to unquoted failed pathname expansions in a command before executing it?

I was exploring the tracing of commands using set -x (set +x to unset) in bash: Print a trace of simple commands, for commands, case commands, select commands, and arithmetic for commands and ...
2
votes
6answers
121 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.
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votes
1answer
42 views

Remove directory without `rm -r`

How to remove non-empty directory without using rm -r or find -delete ? I think it is related to unlink, perl or inode
2
votes
3answers
93 views

creation of user add

I'm having more then 59 servers I need to create a script for user add. purpose: if I'm creating a user in one server it will be reflected on all 59 servers. How can I accomplish this?
8
votes
2answers
238 views

Why does 'nohup command >& /dev/null' seem to “work” in some shells?

I edited an answer on Ask Ubuntu that was suggesting the following nohup gedit >& /dev/null & When they actually meant nohup gedit &> /dev/null & Now, the latter ...
0
votes
3answers
64 views

echo bytes to a file

I'm trying to connect my rasberry Pi to some display using the i2c bus. To get started I wanted to manually write stuff, bytes in particular to a file. How do you write specific bytes to a file? I ...
1
vote
2answers
67 views

Free disk space from a JBoss log file which is still being written to

Is there any locking on the content, imposed by the process if at all the process is using the file. We host a JBoss app server on a RHEL 6.4 OS and due to the disk space constraints we have decided ...
3
votes
1answer
64 views

chmod + silent mode + how force exit code 0 in spite of error

Is it possible execute chmod and ignore error from command Example ( remark file.txt not exsist to show the example ) When I type chmod 777 file.txt I get error on the output chmod: cannot ...
3
votes
3answers
340 views

if/then/else man page

I would like to know if there is any man page documenting the construction of the most basic script commands like if/then/else, while, for each, and all the relative switches, like -eq, -e, -ge, and ...
1
vote
1answer
290 views

Exit of “> ” mode in Unix shell

In sh (not Bash), how would we abort execution of command when the prompt is in > mode? For example, when entering a string with quotes only at the beginning, it makes the prompt look like >, ...
1
vote
7answers
133 views

what are some uses of .(single period) & ..(double period) in the shell command line

The single period . means current working directory The double period .. means parent of the current working directory I can only think of . being used in relative pathname etc cd ./bin/usr How are ...
4
votes
2answers
353 views

Where is a shell script run from?

I have a shell script in /usr/bin. Let's call it hello. It contains this: echo "I am located in $PWD" echo "I am called from this directory: ???" Running hello from /home/Documents I expect the ...
1
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2answers
56 views

Script always runs two instances

I was just curious, what may be the reason why script run two instances when executed. Whenever I run my script foo.sh, and when I check using: $ ps -ef | grep foo.sh It always returns two ...
13
votes
3answers
258 views

What are the responsibilities of each Pseudo-Terminal (PTY) component (software, master side, slave side)?

I am trying to figure out how a tty works1 (the work-flow and responsibilities of each elements). I have read several interesting articles about it, but there are still some blurry areas. This is ...
3
votes
1answer
132 views

adduser: Specify only one name in this mode

I'm trying to add a user with this command on my debian server: #!/bin/bash APPUSER="test1" APPGROUP="test2" # User adduser -c 'uwsgi user' --group $APPGROUP --system --no-create-home ...
2
votes
3answers
58 views

Disable login for useradd [duplicate]

I tried to disable login for a user account but got this error in debain: useradd: unrecognized option '--disabled-login' What is the equivalent of this command for useradd? Do I have to pick ...
0
votes
3answers
72 views

remove new lines

My input is a csv file like this: 10,"Special Projects,bangaram",0,,0 10,"Statutory/ Internal Audit , MO reporting (incl Excel Spreadsheet uploadation) ", bangaram,0,,0 10,"Complience with ...
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votes
2answers
103 views

how to execute a python program in a shell script

I have a python program in that I wrote some python code (disk.py). I executed this program using the command python disk.py in a terminal, it worked. Now I want to execute it using a shell script.