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

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Decoding URL encoding (percent encoding)

I want to decode URL encoding, is there any built-in tool for doing this or could anyone provide me with a sed code that will do this? I did search a bit through unix.stackexchange.com and on the ...
7
votes
2answers
638 views

What does this ${@:2} mean in shell scripting

I see this in a shell script. variable=${@:2} What is it doing?
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3answers
30k views

How to rename multiple files in single command or script in Unix? [duplicate]

I have the below list of files aro_tty-mIF-45875564pmo_opt aro_tty-mIF-45875664pmo_opt aro_tty-mIF-45875964pmo_opt aro_tty-mIF-45875514pmo_opt aro_tty-mIF-45875524pmo_opt that I need to rename to ...
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7answers
3k views

Bash - Continuous String Manipulation

#!/bin/bash FILE="$(basename "$1")" FILE="${FILE/%.jpeg/.jpg}" Is there anyway to glue these two lines together into a one-liner?
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3answers
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which shell will sudo use to execute a shell script without the shebang line

My environment is Ubuntu 12.04 LTS, and the sudo version is 1.8.3p1. First I login as a normal user: $ whoami fin $ cat /etc/passwd | grep -i "root\|fin" root:x:0:0:root:/root:/bin/bash ...
7
votes
5answers
451 views

List out strings which are substrings of other strings in the list

I have a list of names like so: dog_bone dog_collar dragon cool_dragon lion lion_trainer dog I need to extract out names that appear in other names like so: dragon lion dog I looked through the ...
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3answers
4k views

How to run a script from another path, and know the script's path?

I need to run a script that access a file in the same path it is located. For example: I have the script in /home/me/folder/script.sh, and this script will access the file /home/me/folder/myfile. As ...
7
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2answers
872 views

Was there a '\0' at the end of every script?

I'm wondering how did you dertermine the end of a script/file? I'm especially interested for old Unix versions (like V6). Is there a '\0' after the last written character?
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4answers
8k views

Check if $REPLY is in a range of numbers

I'm writing a shell script for Linux, using Bash, to translate any video-file into a MP4. For that, I'm using avconv with libvorbis for audio. Inside my script, I have a question for the user : ...
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3answers
161 views

Is there a way to make this one-liner faster?

Context I have a directory of thousands of zip files that are dated in the form YYYYMMDD_hhmmss.zip and each about 300K. Within each zip file is about 400 xml files each about 3K. The problem I ...
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3answers
3k views

What's the difference between Ctrl-Z and kill -STOP?

When I run a command (make on a large project) from the shell, I can type Ctrl-Z to stop the process and return to the shell. Subsequently, I can run fg to continue the process. I'm trying to write a ...
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3answers
7k views

Rename files in the local folder adding a prefix or suffix

I have many files in a folder and I want to add either prefix or a suffix (not both) to them. I checked here and found out I can use for filename in *.jpg; do mv "$filename" "prefix_$filename"; done; ...
7
votes
3answers
3k views

Loop through the lines of two files in parallel [closed]

The object of the script I'm making is to compare two series of files. The file names are themselves stored into two separate files, one path per line. My idea is to have two while read loops, one for ...
7
votes
1answer
731 views

Bash script doesn't read input

I have a script that is suppose to run a command in the background, and it does that. The problem is that when the script comes upon a read command, it doesn't pause and accept input. Here it is: ...
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5answers
6k views

Compare two files with first column and remove duplicate row from 2nd file in shell script

I will ask my question with an example. I have 2 files: File #1: 118D FC300_R5_TP FX.B 32775 2112 6 2038 6 2112 0 118E FC300_R5_TP FX.B 32775 2136 7 ...
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votes
3answers
14k views

Terminating a bash shell script running in the background

I often use bash shell scripts to run simple commands for many different files. For example, suppose that I have the following bash shell script, called script.sh, that runs the program/command foo ...
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5answers
4k views

Avoiding busy waiting in bash, without the sleep command

I know I can wait on a condition to become true in bash by doing: while true; do test_condition && break sleep 1 done But it creates 1 sub-process at each iteration (sleep). I could ...
7
votes
4answers
21k views

Appending current date to filename

I'm trying to append the current date to the end of a file name like this: TheFile.log.2012-02-11 Here is what I have so far: set today = 'date +%Y' mkdir -p The_Logs & find . -name The_Logs ...
7
votes
2answers
639 views

Shell Script for going through a dir recursively and chmodding based on conditions of file type

Can anyone point me to either code or a tutorial for writing a shell script that can recursively go through an entire directory structure (starting at the current working directory, or given an ...
7
votes
5answers
21k views

Add lines to the beginning and end of the huge file

I have the scenario where lines to be added on begining and end of the huge files. I have tried as shown below. for the first line: sed -i '1i\'"$FirstLine" $Filename for the last line: sed -i ...
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votes
3answers
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Optimizing a `while` loop

I have created a mini script to reboot my Raspberry Pi upon the push of a button. The script simply uses wiringPi (gpio command) to set pin 0 (pin 17 in Raspberry Pi standard numbering order) to ...
7
votes
1answer
11k views

sudo: unable to execute ./script.sh: no such file or directory

I'm stumped. I have a script in my /home directory which is executable: [user@server ~]$ ll total 4 -rwx------ 1 user user 2608 Jul 15 18:23 qa.sh However, when I attempt to run it with sudo it ...
7
votes
1answer
831 views

Using inotify to monitor a directory but not working 100%

I have written a bash script to monitor a particular directory /root/secondfolder/: #!/bin/sh while inotifywait -mr -e close_write "/root/secondfolder/" do echo "close_write" done When I ...
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1answer
6k views

how to set environment variables from a shell script? [duplicate]

I'm trying to set environment variable through a shell script. Here is the script with various techniques: #!/bin/sh echo "export SOMEPATH=/root/some" >> /root/.bash_profile echo "export ...
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votes
2answers
597 views

Possible to use brace (permutation) and array expansion simultaneously?

Bash's {} brace expansion syntax allows for creating easy permutations # echo {b,c,d}{a,e,i,o,u} ba be bi bo bu ca ce ci co cu da de di do du However it's not clear to me if/how it's possible to ...
7
votes
2answers
21k views

Can I redirect output to a log file and background a process at the same time?

Can I redirect output to a log file and background a process at the same time? In other words, can I do something like this? nohup java -jar myProgram.jar 2>$1 > output.log & Or, is that ...
7
votes
2answers
12k views

In a bash shell script, writing a for loop that iterates over string values

In bash, I know that it is possible to write a for loop in which some loop control variable i iterates over specified integers. For example, I can write a bash shell script that prints the integers ...
7
votes
2answers
2k views

Local variables in zsh: what is the equivalent of bash's “export -n” in zsh

I'm trying to contain the scope of a variable to a shell, and not have children see it, in zsh. For example, I type this in .zshrc: GREP_OPTIONS=--color=always But if I run a shell script with the ...
7
votes
3answers
2k views

Bash: interactive remote prompt

I have a script which connects to a remote server and check if some package is installed: ssh root@server 'bash -s' < myscript.sh myscript.sh: OUT=`rpm -qa | grep ntpdate` if [ "$OUT" != "" ] ; ...
7
votes
1answer
4k views

Trap, ERR, and echoing the error line

I'm trying to create some error reporting using a Trap to call a function on all errors: Trap "_func" ERR Is it possible to get what line the ERR signal was sent from? The shell is bash. If I do ...
7
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2answers
2k views

XFCE or pure X11 commands, toggle compositing immediately without restarting X

How can i disable compositing via the command line? I need to disable temporarily for some games, like Nexuiz, for use in a wrapper script to toggle compositing status.
7
votes
1answer
394 views

ftp and shebang

Is there a way to shebang-ify ftp and write small ftp scripts? For example: #!/usr/bin/ftp open 192.168.1.1 put *.gz quit Any thoughts?
7
votes
1answer
273 views

“w | tail” chops text at right margin (78 characters)

Summary: w | tail chops rows after 78th column. When I run the "w" command, it works as expected. However, when I pipe the output to "tail", it chops the output to 78 columns wide (truncates anything ...
7
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3answers
721 views

shell scripts are still working without #!(sha-bang line)

I am new to shell scripts and many books have written that use #!(sha-bang) line in starting of the script to invoke the interpreter .And this will invoke a new shell for script and do the ...
7
votes
3answers
2k views

Script to toggle setxkbmap

I would like a bash script that toggles between: setxkbmap se and setxkbmap us. Then my intentions are to map that script to CtrlEsc through the Keyboard > custom shortcuts. The point is that I ...
7
votes
3answers
14k views

How to set global environment variables at boot through a script, and have them available for an application that runs before login?

I have a service that runs at boot, and in that service it calls a bash script in the background that exports some environment variables. The problem I'm having is that those environment variables ...
7
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3answers
914 views

How to enable safeguards for CPU temperature

My desktop has a nasty habit. When I have several high intensity applications running and my CPU is at maximum usage for a period of time, the core temperature rises and my computer auto-shuts off. ...
7
votes
1answer
2k views

Converting html table into ncurses-like ascii table?

I have some documentation in an html table. I want to convert the table to an ascii table, like you see when you get a mysql command line result back, like this: +------------+------------+ | header ...
7
votes
7answers
187 views

What is the purpose of having two variables ($@,$*) to transmit the arguments of a command into a script? [duplicate]

I have read of the special variables used in a script $@ and $*. As far as I understand, the arguments used while executing the script are stored into two special variables, once all arguments into $@ ...
7
votes
2answers
598 views

Is there a way to convert a zip to a tar without extracting it to the filesystem?

Is there a way to convert a zip archive to a tar archive without extracting to a temporary directory first? (and without writing my own implementation of tar or unzip)
7
votes
1answer
393 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 ...
7
votes
4answers
5k views

Preserve directory structure when moving files using find

I have created the following script that move old days files as defined from source directory to destination directory. It is working perfectly. #!/bin/bash echo "Enter Your Source Directory" read ...
7
votes
4answers
5k views

Parallel execution of a program on multiple files

I have a small script that loops through all files of a folder and executes a (usually long lasting) command. Basically it's for file in ./folder/*; do ./bin/myProgram $file > ./done/$file ...
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votes
3answers
2k views

Mass .flac --> .mp3 transcoding: How to write a shell script that preserves ID3 tag information?

In recent weeks I've gone from a fairly 'hands-on' approach to .flac --> .mp3 transcoding, to one that's far more 'set & forget'. The first step was to stop using a GUI front end (Audacity with a ...
7
votes
4answers
11k views

Copy/rename multiple files using regular expression (shell script)

I have a collection of files matching a pattern such as 'assignment02.cc', 'assignment02.h', 'assignment02.txt', etc. I would like to copy/rename these files into 'assignment03.cc', 'assignment03.h', ...
7
votes
2answers
424 views

Strip // Comments From Files

What's the best way to strip all code comments in a given directory? I'd like to strip out all // ... EOL comments, and /* blah \*/ (or /** ... \*/) comments as well. This is a PHP project, and I'd ...
7
votes
2answers
364 views

Determine dynamically allocated port for OpenSSH RemoteForward

Question (TL;DR) When assigning ports dynamically for remote forwarding (a.k.a. -R option), how can a script on the remote machine (for instance sourced from .bashrc) determine which ports were ...
7
votes
4answers
2k views

redirect and log script output

I am trying to tidy up the following snippets, design goals are to log all output from a script, and should not be a wrapper. Less lines are better. I don't care about user inputs (at this stage), ...
6
votes
8answers
745 views

How do I construct a list with numbers like this?

How do I construct a list like this: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Where I run command 15 or something. Or if I specify 100 it would make it with 100 numbers or 10000 and it would make it ...
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votes
10answers
2k views

Copy only Specific text of a file to another

I have a file abc.txt the contents are <classpathentry kind="src" path="Sources"/> <classpathentry kind="con" path="WOFramework/ERExtensions"/> <classpathentry kind="con" ...