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

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8
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2answers
8k views

Remove end of line characters from stdout? Multiple lines into a single line

I have a script which outputs the following text. This is the output from a Netopia 2210-02 ADSL2 modem. ADSL Line State: Up ADSL Startup Attempts: 1 ADSL Modulation: DMT ADSL Data ...
8
votes
6answers
733 views

A bash function that takes argument like other languages?

I have a bash function to set the $PATH like this -- assign-path() { str=$1 # if the $PATH is empty, assign it directly. if [ -z $PATH ]; then PATH=$str; # if the $PATH does ...
8
votes
2answers
6k views

How can I remove an element from an array completely?

unset array[0] removes the element but still if I do echo ${array[0]} I get a null value moreover there are other ways of doing this but if an element of an array contains spaces like below ...
8
votes
4answers
3k views

exit shell script from a subshell

Consider this snippet: stop () { echo "${1}" 1>&2 exit 1 } func () { if false; then echo "foo" else stop "something went wrong" fi } Normally when func ...
8
votes
3answers
7k views

getopt, getopts or manual parsing - what to use when I want to support both short and long options?

Currently I'm writing a Bash script which has the following requirements: it should run on a wide variety of Unix/Linux platforms it should support both short and (GNU) long options I know that ...
8
votes
2answers
195 views

How do I elevate privileges in the middle of pipeline?

My guess was as follows: echo "Generating some text" | su - -c cat >/output/file But su says: su: must be run from a terminal What would you do?
8
votes
4answers
773 views

What is the easiest way to execute text from tail at the command line?

Sometimes I'm working on a new (ubuntu) box and I type git and am alerted: The program 'git' is currently not installed. You can install it by typing: apt-get install git-core If that happens I ...
8
votes
3answers
3k views

Creating a Bash script that will execute a program and if it exits without crashing, will run it again

I'd like to know the easiest way of creating a bash script that will run an app in MacOSX (it's a UNIX based system so I assumed this was the right place). wait for the program to exit. If the exit ...
8
votes
5answers
2k views

How to run part of a script with reduced privileges?

I have the following problem: On every machine running Postgresql there is a special user postgres. This user has administrative access to the database server. Now I want to write a Bash script that ...
8
votes
4answers
7k views

find -exec in bash script with variable expansion

I'm trying to run a command similar to the one below in a bash script. It should search through all subfolders of $sourcedir and copy all files of a certain type to the root level of $targetdir. ...
8
votes
6answers
8k views

Find biggest files or directories

Which command will print the sizes of all files and directories in the tmp directory (including hidden ones) and sort them by sizes from largest to smallest in human readable format (e.g. 2 GB)? The ...
8
votes
4answers
16k views

printing colored text using echo

I know that for printing a colored text using echo, for example red color, the code is: echo -e "\e[1;31m This is red text \e[0m" and I know that in this example, 31 is code of red color and the ...
8
votes
4answers
310 views

Do you prefer bash scripts or aliases for shortcuts?

I have a ~/bin directory (which is on my PATH) where I store a lot of little 1 or 2 line scripts. Some of them just cd into a directory and run a command on a file, like vim or something. But I also ...
8
votes
1answer
1k views

Suppress output unless non-zero exit code

What's the best way to suppress output (stdout and stderr) unless the program exits with a non-zero code? I'm thinking: quiet_success() { file=/tmp/suppressed if ! ( "$@" > "$file" ...
8
votes
2answers
359 views

Cache all gpg subkey passwords at once? Prevent need for multiple gpg password entry?

Can I enter my gpg password just once and unlock all my sub keys (signing, decryption, authentication)? At the moment, I need to enter my gpg password three times (for signing, for decryption, for ...
8
votes
3answers
188 views

POSIX compliant way to work with a list of filenames possibly with whitespace

I have seen Bash scripting guides suggesting the use of array for working with filenames containing whitespace. DashAsBinSh however suggests that arrays are not portable so I am looking for a POSIX ...
8
votes
0answers
209 views

how to get exit status from the command before the last [duplicate]

I have solaris machine ( solaris 10 ) please Look on the following simple commands (haconf -makerw | grep -iq "Cluster already writable") # haconf -makerw VCS WARNING V-16-1-10364 Cluster ...
7
votes
7answers
793 views

Slick one-liner to convert a list like “1: 2, 3, 4, 5” to “1.2, 1.3, 1.4, 1.5”

Let's say I have a file that looks something like this: 23: a, b, c, d 24: b, d, f 25: c, g and I want to get output like this: 23.a 23.b 23.c 23.d 24.b 24.d 24.f 25.c 25.g Of course it's not ...
7
votes
2answers
537 views

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

I see this in a shell script. variable=${@:2} What is it doing?
7
votes
7answers
2k views

cron Vs. sleep - which is the better one in terms of efficient cpu/memory utilization?

The Case: I need to run some commands/script at certain intervals of time and for this I have two options - 1. set up a cron-job or, 2. implement a loop with sleep in the script itself. Question: ...
7
votes
7answers
2k 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?
7
votes
5answers
418 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 ...
7
votes
4answers
2k views

How to run parallel processes and combine outputs when both finished

I have a bash shell script in which I pipe some data through about 5 or 6 different programs then the final results into a tab delimited file. I then do the same again for a separate similar dataset ...
7
votes
3answers
2k views

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
30k views

How can I monitor all outgoing requests/connections from my machine?

My machine is a server so I want to ignore connections being made to my server (e.g. when someone visits my website). I want to see only connections/requests being made by my server to other places. ...
7
votes
3answers
2k views

Use & (ampersand) in single line bash loop

I have been using this command successfully, which changes a variable in a config file then executes a Python script within a loop: for((i=114;i<=255;i+=1)); do echo $i > numbers.txt;python ...
7
votes
3answers
152 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 ...
7
votes
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 ...
7
votes
1answer
645 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: ...
7
votes
3answers
9k views

Passing named arguments to shell scripts

Is there any easy way to pass (receive) named parameters to a shell script? For example, my_script -p_out '/some/path' -arg_1 '5' And inside my_script.sh receive them as: # I believe this ...
7
votes
5answers
4k 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 ...
7
votes
4answers
10k views

How do I append text to the beginning and end of multiple text files in Bash?

I have a directory full of text files. My goal is to append text to the beginning and end of all of them. The text that goes at the beginning and end is the same for each file. Based on code I got ...
7
votes
2answers
572 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
3answers
1k views

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
7answers
17k views

Show sum of file sizes in directory listing

The Windows dir directory listing command has a line at the end showing the total amount of space taken up by the files listed. For example, dir *.exe shows all the .exe files in the current ...
7
votes
2answers
462 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
5answers
15k 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 ...
7
votes
1answer
2k 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 ...
7
votes
1answer
3k 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
votes
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
369 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
253 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
votes
3answers
664 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
2answers
891 views

Check bash/shell script dependencies

Is there a method/command to check for the dependencies of a bash script? In other words, a response to this question : Which libraries should a user install to run the script? I can do this ...
7
votes
6answers
23k views

How to compare two dates in a shell

How to compare two dates in a shell script? For example something like todate=2013-07-18 cond=2013-07-15 if [ $todate -ge $cond ]; then break fi It doesn't work. ...
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
1answer
1k views

Are dash, ash and sh script 100% compatible?

I wanted to know whether scripts written for dash, ash, and sh are 100% compatible? Are there any added features to dash or ash, or syntax change? From what I heard, ash is a direct descendant of ...
7
votes
3answers
12k 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
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
1answer
3k views

How can I tell whether a package is installed via yum in a bash script?

I am trying to write a script that installs packages, but if it fails at any point later in the script rolls back whatever it installed. Of course if the user has already previously installed a ...