Questions tagged [scripting]
A script is a sequence of commands or instructions that are executed by an interpreter program rather than compiled into a standalone executable program.
502
questions
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11
answers
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Allow setuid on shell scripts
The setuid permission bit tells Linux to run a program with the effective user id of the owner instead of the executor:
> cat setuid-test.c
#include <stdio.h>
#include <unistd.h>
int ...
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151
votes
3
answers
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Have backticks (i.e. `cmd`) in *sh shells been deprecated?
I've seen this comment many times on Unix & Linux as well as on other sites that use the phrasing "backticks have been deprecated", with respect to shells such as Bash & Zsh.
Is this ...
slm♦
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114
votes
5
answers
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Does the shebang determine the shell which runs the script?
This may be a silly question, but I ask it still. If I have declared a shebang
#!/bin/bash
in the beginning of my_shell_script.sh, so do I always have to invoke this script using bash
[my@comp]$...
- 2,069
141
votes
11
answers
372k
views
Script to change current directory (cd, pwd)
I want to run a script to simply change the current working directory:
#!/bin/bash
cd web/www/project
But, after I run it, the current pwd remains unchanged! How can I do that?
- 1,513
229
votes
9
answers
299k
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Looping through files with spaces in the names? [duplicate]
I wrote the following script to diff the outputs of two directores with all the same files in them as such:
#!/bin/bash
for file in `find . -name "*.csv"`
do
echo "file = $file";
diff $...
- 7,113
63
votes
16
answers
264k
views
Automatically run commands over SSH on many servers
There is a list of IP addresses in a .txt file, ex.:
1.1.1.1
2.2.2.2
3.3.3.3
Behind every IP address there is a server, and on every server there is an sshd running on port 22. Not every server is ...
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647
votes
4
answers
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Using "${a:-b}" for variable assignment in scripts
I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation
VARIABLE1="${VARIABLE1:-some_val}"
or some expand ...
- 7,369
44
votes
14
answers
30k
views
Using notify-send with cron
I am using Arch Linux with KDE/Awesome WM. I am trying to get
notify-send to work with cron.
I have tried setting DISPLAY/XAUTHORITY variables, and running notify-send with "sudo -u", all without ...
- 455
103
votes
6
answers
233k
views
Using while loop to ssh to multiple servers
I have a file servers.txt, with list of servers:
server1.mydomain.com
server2.mydomain.com
server3.mydomain.com
when I read the file line by line with while and echo each line, all works as expected....
- 122
31
votes
4
answers
142k
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Storing output of command in shell variable [duplicate]
I have an operation using cut that I would like to assign result to a variable
var4=echo ztemp.xml |cut -f1 -d '.'
I get the error:
ztemp.xml is not a command
The value of var4 never gets ...
- 5,271
11
votes
4
answers
43k
views
How to use wc and piping to find how many files and directories are in a certain directory?
How can I use word counter (wc) and piping to count how many files or directories are in the /usr/bin directory?
- 173
7
votes
4
answers
12k
views
Print two files in two columns side-by-side
I want to output two text files in two columns — one on the left side and other one on the right.
paste doesn't solve the problem, because it only insert a character as delimiter, so if the first file ...
- 481
120
votes
13
answers
155k
views
Replace environment variables in a file with their actual values?
Is there an easy way to substitute/evaluate environment variables in a file? Like let's say I have a file config.xml that contains:
<property>
<name>instanceId</name>
<...
- 1,307
49
votes
7
answers
32k
views
What Unix commands can be used as a semaphore/lock?
I want to run multiple Bash shell scripts in parallel. However, I want to avoid race conditions. What Unix commands are truly atomic that I could use for this purpose, and how can I use them?
- 2,635
87
votes
8
answers
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views
Multiple arguments in shebang
I am wondering whether there is a general way of passing multiple options to an executable via the shebang line (#!).
I use NixOS, and the first part of the shebang in any script I write is usually /...
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74
votes
3
answers
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views
Shebang line with `#!/usr/bin/env command --argument` fails on Linux
I've got a simple script:
#!/usr/bin/env ruby --verbose
# script.rb
puts "hi"
On my OSX box, it runs fine:
osx% ./script.rb
hi
However, on my linux box, it throws an error
linux% ./script.rb
/usr/...
- 1,589
635
votes
24
answers
703k
views
Repeat a Unix command every x seconds forever
There's a built-in Unix command repeat whose first argument is the number of times to repeat a command, where the command (with any arguments) is specified by the remaining arguments to repeat.
For ...
- 6,499
12
votes
2
answers
6k
views
Piping for loop output prevents local variable modification
I'm trying to write a simple bash function that takes, as its arguments, a number of files and/or directories. It should:
Fully qualify the filenames.
Sort them.
Remove duplicates.
Print all that ...
- 223
11
votes
1
answer
11k
views
How does this find command using "find ... -exec sh -c '...' sh {} +" work?
@StephaneChazelas posted the following solution to this Q&A: Having some trouble using “find -exec {} +”.
$ find . -iname "*.extension" -exec sh -c '
exec <command> "$@" <additional ...
slm♦
- 364k
4
votes
6
answers
38k
views
Check for Process if Same is Running
Is there a script or a way in linux that when I try to execute a shell script/process, if the same is running, it will prompt that same is running and will exit otherwise it will continue.
- 325
141
votes
3
answers
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Pass command line arguments to bash script
I am new to bash script programming.
I want to implement a bash script 'deploymLog', which accepts as input one string argument(name).
[root@localhost Desktop]# ./deploymLog.sh name
here I want to ...
chinchu
115
votes
2
answers
361k
views
su options - running command as another user
I was wondering how to run a command as another user from a script.
I have the script's owner set as root. I also have the following command being run within the script to run the command as the ...
- 1,385
46
votes
7
answers
4k
views
What's a good mnemonic for shell double vs. single quotes?
I don't do enough scripting to remember, without looking up, whether double or single quotes result in a Unix variable being substituted.
I definitely understand what is going on. My question is does ...
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127
votes
3
answers
92k
views
What does it mean to have a $"dollarsign-prefixed string" in a script?
I just saw this in an init script:
echo $"Stopping Apache"
What is that dollar-sign for?
My research so far:
I found this in the bash manual:
extquote
If set, $'string' and $"string&...
- 1,373
48
votes
3
answers
62k
views
Using the setuid bit properly
I have a process that needs root privileges when run by a normal user. Apparently I can use the "setuid bit" to accomplish this. What is the proper way of doing this on a POSIX system?
Also, how ...
- 86.6k
28
votes
1
answer
9k
views
How to implement a horizontal cat? [duplicate]
Standard cat concatenates files line by line (row by row, if you will). I find myself needing a horizontal cat command more and more often recently; i.e. a command that takes a list of files and ...
- 3,699
23
votes
8
answers
43k
views
History command inside bash script
History is a shell-built in command I couldn't able to use that within a BASH script. So, Is there a way attain this using BASH script ?
Here we go my script for you:
#!/bin/bash
history | tail -100 ...
10
votes
4
answers
31k
views
Print a string including single quotes and other special characters
How can I write this with an AIX script correctly? My requirement is to write this command in test.txt:
clock=$(prtconf -s | awk '{print $4,$5}')
I tried this command:
print 'clock=$(prtconf -s | ...
- 311
6
votes
2
answers
2k
views
How does bash interpret the equal operator with no surrounding spaces in a conditional?
The following script does not behave as I would have expected. Adding spaces around the '=' in the conditional made it perform how I wanted, but it got me thinking, what is it actually doing inside ...
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4
votes
3
answers
18k
views
Run a GUI program at startup
I am using Ubuntu 14.04. I wrote a small script named trial. The contents of the script are as follows:
#!/bin/sh
SHELL=/bin/sh
PATH=/bin:/sbin:/usr/bin:/usr/sbin
sh -c firefox
I copied the ...
- 161
169
votes
4
answers
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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 ...
- 2,407
61
votes
7
answers
181k
views
Execute remote commands, completely detaching from the ssh connection
I have 2 computers, localpc and remoteserver.
I need localpc to execute some commands on remoteserver. One of the things it needs to do is start a backup script that runs for a number of hours. I ...
- 1,715
190
votes
6
answers
477k
views
how can I add (subtract, etc.) two numbers with bash?
I can read the numbers and operation in with:
echo "First number please"
read num1
echo "Second number please"
read num2
echo "Operation?"
read op
but then all my attempts to add the numbers fail:
...
- 41.3k
24
votes
3
answers
80k
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 ...
- 4,821
18
votes
8
answers
37k
views
Add something to crontab programmatically (over ssh)
I have a deployment script.
It must add something to a user crontab
(trigger a script that cleans logs every XXX days);
however, this must be done only during the first deployment,
or when it needs ...
- 319
7
votes
1
answer
3k
views
Parallel execution of bash script
I have a table URL_Experiment in my database (mySQL database). I have 2 million URL links in this table.
For each URL, I am checking if some particular text is present in the URL and updating the ...
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3
votes
1
answer
2k
views
Integration of afuse user-level automounter with sshfs as a systemd service spawned from login for local users
Edit 2020: I've been using the systemd-answer posted below for several years now, and am quite happy with it.
To facilitate working with remote files, I setup afuse with sshfs to run from .bashrc of ...
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1
vote
1
answer
969
views
$! not being set to the PID of a > >(...) process substitution used with an external command
Bash 4.4.19(1)-release
I have below a simple script which is the basis for a logging app.
For various reasons I had to use process substitution.
The runner is the heart of the app and since ...
- 457
132
votes
6
answers
474k
views
Confusing use of && and || operators
I was skimming through an /etc/rc.d/init.d/sendmail file (I know this is hardly ever used, but I'm studying for an exam), and I've become a bit confused about the && and the || operators. I'...
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70
votes
12
answers
111k
views
Is there a unix command that gives the minimum/maximum of two numbers?
I was looking for a command to limit numbers read in from stdin.
I wrote a little script for that purpose (critique is welcome), but I was wondering if there was not a standard command for this, ...
- 5,745
19
votes
10
answers
40k
views
Extracting nested zip files
I have numerous zip archives, each of which contains a number of zip archives. What is the best way to recursively extract all files contained within this zip archive and its child zip archives, that ...
- 2,305
18
votes
3
answers
62k
views
Bash: calculate the time elapsed between two timestamps
I have written a script that notifies me when a value is not within a given range. All values "out of range" are logged in a set of per day files.
Every line is timestamped in a proprietary reverse ...
- 408
15
votes
3
answers
7k
views
Can I use a variable in a Bash brace expansion?
Below is some sort of pseudo-code for what I'm trying to accomplish:
#!/bin/bash
# I already have the variable below figured out (positive integer):
numlines=$([returns number of lines containing ...
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12
votes
5
answers
21k
views
How do you colorize only some keywords for a bash script?
I am running some unit test code. The unit test code outputs regular text. There is a lot of the text so I want to highlight for the user important keywords.
In this case the keywords are "PASS" and "...
- 3,772
7
votes
5
answers
17k
views
Bash script: check if a file is a text file [closed]
I am writing a menu based bash script, one of the menu options is to send an email with a text file attachment. I am having trouble with checking if my file is a text file. Here is what I have:
...
- 73
4
votes
4
answers
6k
views
passing passwords to a script
I want to scp a file to a remote host, and from there, run a command on the file, and exit the remote session. If I write a usual script, call scp and then ssh, I am prompted to enter two passwords. ...
- 303
4
votes
2
answers
2k
views
Commands for determining level of usage of server
I am scripting a new program that will connect to a cluster of machines in a VM park, and hopefully check their level of usage.
The VM clients are a combination of RHEL and CentOS, and runs on ...
- 68
0
votes
1
answer
2k
views
/bin/sh: ./check-dependencies.pl: not found — but check-dependencies.pl exists!
I'm trying to build Moses, but when I run make I get the following output:
minakshi@minakshi-Vostro-3500:~/Desktop/working-dir/moses/scripts$ make release
# Compile the parts
make all
make[1]: ...
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320
votes
5
answers
1.2m
views
How can I get the current working directory? [duplicate]
I want to have a script that takes the current working directory to a variable. The section that needs the directory is like this dir = pwd. It just prints pwd how do I get the current working ...
user104976
70
votes
8
answers
80k
views
AutoHotkey equivalent
Is there an equivalent product/method for AutoHotkey?
For those that don't know, it's a product that allows you to program your mouse movements and keyboard. This allows me to "macro" certain ...
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