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

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5
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3answers
159 views

Auto increment filename

I have a need to collect some duplicate files and want to avoid name collisions. The problem is that this collection of files might be added to by another execution of my script before the files are ...
5
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3answers
338 views

How to prevent bash command substitution output from being escaped?

I am trying to use command substitution in a bash script to output redirection symbols based on a variable like so: IS_VERBOSE=false curl $BLAH $( $IS_VERBOSE && echo '-i' || echo '> ...
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votes
1answer
4k views

Bash script error: integer expression expected

I have a problem with a bash script on raspberry pi: x='gpio -g read 22' if [ $x -ge 1 ] then gpio -g write 23 1 fi The error is integer expression expected. Why?
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votes
5answers
5k views

How can I copy a file in a bash script and rename it while copying and place it in the same directory

How would I copy a file "file.doc" and rename it while copying to "file_copy.doc" and place it in the same directory ? And this only by calling the script and adding the file name in the argument: ...
5
votes
1answer
407 views

How do I store colored text in a variable and print it with color later?

If I do git status --short, git lists files that are not tracked with two red question marks in front: I'm trying to store this in a variable and print it with color later. Here's my bash script: ...
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votes
3answers
4k views

Split the lines of a text file into separate files

I have a text file that looks something like this: foo bar zip rar tar I need to use a bash script on OSX to make a new text file after every new line like this: cat text1.txt foo cat text2.txt ...
5
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3answers
98 views

How to put the output of the trailing lines of grep in on-line?

Assuming that I have this file: Thu May 8 15:32:07 2014 User-Name = "Mark" Framed-IP-Address = 0.0.0.0 Acct-Status-Type = Interim-Update Acct-Input-Octets = 95684 ...
5
votes
1answer
2k views

ifconfig -a in a shell script

I am writing a shell script to start my network in my virtual machine on boot, since it does not do this right away for some reason with a snapshot of a virtual machine. Since the eth device starts ...
5
votes
2answers
213 views

How would I add a prefix to input I receive from a pipe via awk and color the prefix conditionally?

Is there a way to add a prefix to lines received (and filtered) via awk - yes I know that's possible so far - and then conditionally (e.g. based on the existence of the $PS1 variable of the ...
5
votes
2answers
880 views

Make a directory for each row within the given text file?

I'm trying to write a bash shell script that will read the data from a given (as an argument) file, and for each row in the file, make a sub-directory under the given (as an argument) directory. The ...
5
votes
2answers
2k views

Get the PID of file creation

I am writing a bash script that creates 5 files with the extension ".P" and write a line of "something" into them. "P" represents a number and it's the PID of the process that creates the file. How ...
5
votes
3answers
2k views

Quote a variable in shell script “if” statement

e.g. if [ "$FOO" = "true" ]; then vs if [ $FOO = "true" ]; then What is the different? Seems both of two statements also works.
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3answers
10k views

Bash script that automatically kills processes when CPU/memory usage gets too high

I have created a script that kills processes if CPU and/or memory usage hits 80%. It creates a list of killed processes when this happens. What can I do to improve it? while [ 1 ]; do echo echo ...
5
votes
3answers
200 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 ...
5
votes
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
votes
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 ...
5
votes
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 ...
5
votes
3answers
668 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?
5
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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 ...
5
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
votes
1answer
219 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)' ...
5
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3answers
289 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
407 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
436 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
votes
1answer
260 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
227 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
203 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 ...
5
votes
2answers
45k 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
167 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
307 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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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
votes
1answer
919 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?
5
votes
3answers
909 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?
5
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5answers
2k views

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, ...
5
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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
votes
1answer
558 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
458 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
166 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
1k 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 ...
5
votes
6answers
721 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 ...
5
votes
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
votes
1answer
390 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
votes
1answer
570 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
82 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 ...