Questions about shell scripts, executable files that are interpreted by a shell (bash, zsh, etc.).

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3answers
197 views

SSH to two addresses, use the one that connects first

I have a home computer (let’s call it franklin because that’s what I call it) that I often ssh into from my work laptop. When I’m at home, I ssh to franklin.local, and when I’m at work or anywhere ...
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4answers
2k views

GUI input for shell script

I have a shell script which installs a program in RedHat. I need to add a GUI for entering some parameters so that it looks like an installation wizard . I tried Xdialog, Zenity, and Yad, but they ...
5
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1answer
2k views

How to create a confirmation question in Linux?

I have a certain command (git push server-name) that has major consequences. How to require confirmation for this command only? It should ignore white space. The confirmation could be Enter 'yes i am ...
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3answers
2k views

killing processes automatically

I need to kill all processs in a certain shell excluding certain processes. Like sh which is my shell. And the comand. This is what currently in my shell right now. rcihp146 :/home/msingh2> ps ...
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3answers
649 views

How do I prevent a script from terminating when the shell exits?

In particular, I created a script to start Firefox which I double-click and choose 'Run in terminal,' but when the shell exits Firefox is killed immediately. How do I prevent this from happening?
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1answer
4k views

Split video file into pieces with ffmpeg

When you want to extract two minutes of a video file from minute 2 to minute 4, you will use command ffmpeg -i input.mpg -sameq -ss 00:02:00 -t 00:02:00 output.mpg I'd like to split the video into ...
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votes
2answers
6k views

Using nohup at /etc/init.d/service

I have been trying to create a daemon using /etc/init.d/myservice and it will call a shell script that contains nohup within the script line. Will it affect it if I could do service stop later?
5
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1answer
201 views

Sort output of awk except for first line?

This is a use case I am continually running into in parsing CSV files. When it is an inline awk script embedded in a shell script, I can use this workaround: myfile=$(mktemp) awk '(awk script here)' ...
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3answers
259 views

Go from a String to an Array of “words” in Bash

I need to go from a string to an array where each entry is each word on that string. For example, starting with: VotePedro="Vote for Pedro" I need the array: Vote For Pedro Which I should then ...
5
votes
1answer
3k views

Shell command/script to see if a host is alive?

I'm trying to figure out more ways to see if a given host is up, solely using shell commands (primarily bash). Ideally, it would be able to work with both hostnames and IP addresses. Right now the ...
5
votes
2answers
402 views

Two-words argument in shell script

I have a problem with a shell script. It is supposed to read arguments: index, date, time1 (the beginning of the interval), time2 (the end of the interval). It should count how many times the ...
5
votes
1answer
427 views

echo colored text which changes colors dynamically

Is there any way that i can print a colored text on console which keeps on changing its colors dynamically(with or without a specified time interval) just like some greeting cards in which the ...
5
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1answer
250 views

How to make sure only one instance accessing the file at a time in a folder?

I have a shell script which will be executed by multiple instances and if an instance accessing a file and doing some operation how can I make sure other instances are not accessing the same file and ...
5
votes
2answers
224 views

What's the difference between 'expansion' and 'substitution' in terms of shell programming's terminology?

Expansion and Substitution seems to be interchangeble at same context in shell programming language. For example, some documents such as Bash reference manual, Bash Hackers Wiki use the word ...
5
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3answers
192 views

how do I set quotes around a variable so that the programs sees them as quote marks

I am trying to get quotes around a variable to make is just like I typed it in the terminal to get this script to work. it shows " quotes around the varibale " but still does not see it as quotes, as ...
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2answers
44k views

Assigning the output of a SQL query to variable

I am connecting to oracle database and firing a query and assigning the output to variable But when I echo the value of the variable it doesn't get printed correctly. count=`sqlplus -s ...
5
votes
2answers
5k views

Graphically ask for password in a bash script and retain default sudo timeout setting

The sudo -A (SUDO_ASKPASS) option apparently causes sudo to lose the timeout (e.g., timestamp_timeout) setting. I want to use the sudo -A option but I want to retain the default timeout (e.g., 15 ...
5
votes
1answer
164 views

What do you use the -t “tag” option for in logger?

When using the "logger" command to write messages to the system logs from scripts, I use the -t "tag" to store the scripts name along side the message it's written to the log. I do this to make ...
5
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2answers
305 views

[ vs [[ : which one to use in bash scripts? [duplicate]

The zsh man page, in its section on test (aka [), explicitly advises against using it at all, and urges readers to use [[ whenever possible. The relevant section states: The command attempts to ...
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votes
3answers
1k views

Linux command line that will fail if any standard out is produced

Is there a simple utility which I can pipe output to on Linux that will: Return a success code if there is no output on standard out (and / or standard error). Return a failure code if output is ...
5
votes
3answers
4k views

sed: multi-line replace of config block

I have some configuration files that basically look like (...content...) # BEGIN DYNAMIC BLOCK - DO NOT EDIT MANUALLY (... more content ...) # END DYNAMIC BLOCK (... even more content ...) Now, in ...
5
votes
3answers
9k views

How can I check if mysql is installed using a bash script?

I need to check if mysql is installed from within a bash script. What would be an efficient way of doing that? I thought I could do this: if [ ! -f `which mysql` ] ; then echo "foo" fi But I ...
5
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1answer
906 views

How to find out how many cores (including emulated via HT and such) are avaliable to user?

I wonder how to get how many cores (including emulated via HT and such) are avaliable to user via bash shell-script command?
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3answers
2k views

What's the best way to determine the working directory for UNIX process using 'ps'?

I am running a Ruby command line script (rufus.sh)which ultimately calls Thread.new, which spawns a UNIX process as shown below. I run this script for more than 1 directory as the output of the ps ...
5
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3answers
894 views

How to specify -? option with GNU getopt

When parsing command line arguments with GNU getopt command, how do I (if possible) do recognize -? as another option? Is there a way to escape it in the opstring?
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5answers
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How to delete files from a folder which have more than 60 files in unix?

I want to put a script in cronjob which will run in a particular time and if the file count is more than 60, it will delete oldest files from that folder. Last In First Out. I have tried, ...
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2answers
4k views

Using Diff on a specific column in a file

Will it be possible to use diff on a specific columns in a file? file1 Something 123 item1 Something 456 item2 Something 768 item3 Something 353 item4 file2 Another 123 stuff1 Another 193 ...
5
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1answer
546 views

While command not found and syntax error near unexpected token [closed]

I am trying to write a shell script that takes a string input from a user, asks for a file name and reports whether that string is present in the file. Below is my current script. #!/bin/bash while ...
5
votes
1answer
446 views

How to catch a signal in command line?

I asked this question. SIGPIPE signal is generated to stop the execution of the command as told in the answer. But how do I capture this signal and gracefully terminate the command? The command exits ...
5
votes
2answers
164 views

Remove specific file from directory if it's the only one

I have a lot of directories and sub-directories. I want to recursively remove one specific file from a directory if it's the only one there. Also assume that there are no sub-directories in that ...
5
votes
1answer
4k views

Automatically detect when a file has reached a size limit

I would like to send an email when a file reach a certain size limit. The only way I thought of doing this is by doing a cronjob which will check the file size and send the email if the file is ...
5
votes
1answer
942 views

Bash capture any error like -e but don't exit, do something else

I want to set a flag in a shell script (bash) so that if anything returns non-zero, a flag is set (i.e. set a variable like errors="True"). So far, I've thought of calling the script with ...
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6answers
695 views

shell script to control the number of processes of an user

I have to launch a total number, NUMTOT of a program (could be any, C, Mathematica, ns-2... mathematical environments). The problem is that the computer where these processes run only admits a ...
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1answer
4k views

How to integrate a multiline awk script in a shell script

I am a beginner in shell scripting and my question is a continuation of How to parse a file to extract 3 digits numbers kept in a "group number" I am trying to integrate in a single shell ...
5
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1answer
379 views

How does having /dev/fd make running shell scripts under sudo safe?

At the end of the man page for sudo, there's the following remark: Running shell scripts via sudo can expose the same kernel bugs that make setuid shell scripts unsafe on some operating systems ...
5
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1answer
563 views

Writing command synopsis in standard man format

I am writing a script and in the usage() function I want to specify the usage. My script uses either option1 or option2 or both. One of them is mandatory. Is there a standard way to write it up?
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1answer
4k views

Cannot open: Input/output error with tar command in a shell script

I am trying to create a tar ball in a shell script (I have enabled set -x), but I get an error: + cd /home5/mysite/public_html + TAR_DUMP=gypo_2012-02-18-03:51:15.tar.gz + echo 'Tar name: ...
5
votes
2answers
77 views

Search directories for multi line string

Looking for a way to recursively search a repository for all files containing a multi line string and return the file names that contain it. The paragraph is just a header approx 30 lines. So I know ...
5
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2answers
97 views

In bash script, what's the different between declare and a normal variable?

In bash scripting: we create variable just name it: abc=ok or we can use declare declare abc=ok what's the different ? and why bash make so many ways to create variable?
5
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2answers
910 views

Mac OS X how to verify particular packages are installed

In a BASH script I need to check if gcc, g++, cpp, make, libpng devel, zlib devel, git, Java (including devel files), ant and pkg-config are available on Mac OS X and if not, I need to prompt user to ...
5
votes
2answers
112 views

Use lines in a file to produce string and file name

I have a file, foo.txt, that has a folder name on each line: folder_1 folder_2 folder_3 And I'd like to do something like this: cat foo.txt | xargs -I {} echo 'function {}() { return stuff; }' ...
5
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1answer
416 views

Proper way to distribute shell scripts

What is the most proper way to distribute shell scripts, if behaviours of shells can be modified by set and thus are unpredictable? For example, rm *.txt wouldn't be executed as expected on the ...
5
votes
1answer
938 views

counting multiple patterns in a single pass with grep?

I've written a grep loop to iteratively count DNA trinucleotides within a gzipped DNA fasta file containing DNA sequences e.g. declare -a tri=(AAA AAC AAG AAT CAA .. etc) for i in ${tri[@]} do ...
5
votes
1answer
402 views

indirect variable expansion in POSIX as done in bash? [closed]

Is it possible, or is there some elegant hack to do indirect variable expansion in POSIX as can be done in Bash? For context, I'm trying to do the following: for key in ${!map_*} do # do ...
5
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2answers
4k views

Is it possible to execute a script as first at shutdown/reboot on Debian?

I am currently trying to register a script (located in the /etc/init.d) in a way that makes this script being executed as the first script/programm at shutdown/reboot (change to running level 0 or 6). ...
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2answers
9k views

How to run sudo commands remotely via ssh -t?

I have a script that logs into a remote host via ssh -t and uses sudo service foo restart. The requirement is to avoid the prompt for a password on the remote host. The remote host authenticates via ...
5
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1answer
6k views

“echo 1 > /sys/block/sdX/device/delete” on all disks except predetermined list

I have a list of scsi disks that I need to remove. The list is considered random at best and changes from time to time. I want to remove everything except a predefined list that I have created. Let's ...
5
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2answers
77 views

Bash wrapper that will format the output of another program

Is there a wrapper or a method to force the output of another program (let's say 7zip) inside a bash script to be formatted in a given way, say, coloured or indented? Or even run in a separate small ...
5
votes
1answer
963 views

Variables outside of while loop

I am trying to echo the variables $f1, $f2, etcetera, outside of the while loop shown below. From what I understand, the scope of the variable is not correct. Therefore I tried a few of the ...
5
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1answer
241 views

How to stop a background process started in the same script, without exit the script?

I have a program that takes a variable time to run (no more than two minutes), and to make it less odious, I put fortune messages. #!/bin/bash ... for i in $(seq 1 45); do sleep 3; echo; echo; ...