Questions specific to GNU’s Bourne Again SHell, as opposed to other Bourne/POSIX shells. For questions about Unix shells in general, use the /shell tag instead.

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0
votes
3answers
30 views

How to save case values in variable

selection= until [ "$selection" = "0" ]; do echo "" echo "PROGRAM MENU" echo "1 - display free disk space" echo "2 - display free memory" echo "" echo "0 - exit program" echo "" echo ...
0
votes
1answer
22 views

how to get the size of an indirect array in bash?

Without using eval. this wont work: astr=(a b c) str="#astr[@]" echo "${!str}"
20
votes
4answers
16k views

combine output from two commands in bash

Is it possible to combine output from these two commands? node ~/projects/trunk/index.js python ~/projects/trunk/run.py run Neither command exits so I'm not sure how to do this.
26
votes
3answers
6k views
+50

Is dash or some other shell “faster” than bash?

I always thought that the only benefit of using dash instead of bash was that dash was smaller, and therefore many instances of dash would start faster at boot time. But I have done some research, ...
1
vote
2answers
766 views

Find last line of a file for matching string?

I want a loop that runs infinitely over a file but always checks the last line to see if it contains the matching string if it does then echo that line and keep the loop running. What I have right now ...
9
votes
2answers
142 views

Shell Syntax: How to correctly use \ to break lines? [duplicate]

I used to believe that the appropriate way of breaking the lines in a list is command1 && \ command2 It turned out that it isn't so , one doesn't need \ $ [ $(id -u) -eq 1000 ] ...
0
votes
2answers
26 views

operate on different sections of stdin without intermediate file

Is there a simple way to do this with redirection or pipes without creating FILE1? I want to apply process2 to the body of the output of process1, without touching the first and last few lines. ...
0
votes
1answer
32 views

How can I make sure that I'm running an updated version of bash?

I'm learning bash using a Mac, and I just attempted to update bash using: brew install bash sudo -s echo /usr/local/bin/bash >> /etc/shells chsh -s /usr/local/bin/bash Now, ...
0
votes
0answers
11 views

Admin scripts for RPi and ODROID XU4 on an automated UAV? [on hold]

Please let me know if this isn't quite the place to ask this; I don't think that Super User was quite the place, so I thought I'd try here. I'm looking for ideas for bash scripts, or just general ...
1
vote
2answers
43 views

How to rename certain directories if the parent has a particular name?

I have to do some global renaming in an Eclipse plugin project, although the fact that the code is Java and it's an Eclipse plugin is irrelevant. Basically, the steps I need to perform are the ...
-1
votes
0answers
53 views

How do I delete everything on my computer with one command using bash? [on hold]

I'm trying to delete every single file and directory on my computer. How do I do so?
7
votes
5answers
4k views

bash script [ x$1 = x ]

I am reading bash script I do not understand what is going there. #!/bin/sh [ x$1 = x ] What is going on the second line and what [ x$1 = x ] mean?
9
votes
5answers
8k views

How can I print only certain commands from a bash script as they are run?

I have a bash script with various if statements based on command line arguments I pass in when calling it. Having some kind of output as to what commands are being run is helpful to confirm the flow ...
3
votes
1answer
25 views

How to always print the prompt on a new line & keep input

We all know this annoying issue: $ printf "abc" > some-file $ cat some-file abc$ which tends to mess up the prompt if it is any more complex than $, throws off the current cursor position and ...
1
vote
2answers
41 views

Combine Two SSH Commands

The first ssh command is done on my computer, I enter the key password, then put the second ssh command in while logged into the server. ssh -i cloudkey -L 6000:localhost:6001 admin@54.152.188.55 -p ...
4
votes
4answers
32k views

Yum update problems on CentOS 6.5 minimal as VMware guest

INFO: I am using Windows 7 Pro (64bit) with VMware Workstation version 10.0.1 . I am using CentOS(64bit) 6.5 minimal, for the first time. I am running this from my workplace network, which may use a ...
3
votes
2answers
48 views

regenerate .bashrc from current shell

So I stupidly inadvertently destroyed ~/.bashrc. If I have open terminals with the settings that were previously there, is there a way to export the current settings back to a new .bashrc? (I've tried ...
1
vote
2answers
41 views

Check in pure bash that the download is complete

short story is, I probably need a simple loop in bash which checks periodically whether the size of a given file has changed or not since last checked. Long story, I will be downloading a file ...
8
votes
5answers
392 views

Is there a tool to dynamically redirect output to a new file on request

I'm currently redirecting the output of a monitoring tool to a file, however what I'd like to do, is to redirect this output to a new file on my request (using a keybinding), without stopping the said ...
2
votes
1answer
47 views

How do I run multiple commands together in the background?

I know I can run a program in the background using &. command & However, I want to run multiple commands, and cd into a different directory while they are running. The multiple commands ...
1
vote
1answer
22 views

How to monitor system performance over time

I wrote the below script to determine how my system is holding up against various games. It checks all the vitals (GPU, RAM, and CPU) and then appends the data to a log file. Is this a reasonable ...
0
votes
1answer
13 views

custom shutdown script in rc6.d does not seem to be working.

I'm working with a software application that's a bit touchy so I wan't to shut the software down automatically on reboot or shutdown. I have created a script an placed it in /etc/init.d/ with a ...
2
votes
1answer
46 views

Differences between declared, defined, and set

In shell, what are the differences between a variable that is declared, defined and set? Does "declared" mean the identifier of the variable exists, but the storage and value of the variable do ...
1
vote
2answers
19 views

How do I remove all files from wtihin a certain directory except for a child directory of that directory?

I’m using bash shell. I have this command to delete all JAR files within a particular directory find ~/.jenkins/jobs/subco/ -name '*.jar' -print0 | xargs -0 -r rm However, I want to modify the ...
116
votes
4answers
131k views

Why do I need a tty to run sudo if I can sudo without a password?

I have configured sudo to run without a password, but when I try to ssh 'sudo Foo", I still get sudo: sorry, you must have a tty to run sudo. Why does this happen and how can I work around it?
0
votes
1answer
41 views

Bash script fail to detect disk

I got a script that is supposed to reformat and mount /dev/disk/by-label/backup_disk into /mnt/backup_disk. Like this: /sbin/mkfs.ext4 -q -L backup_disk /dev/disk/by-label/backup_disk mount -t ext4 ...
3
votes
3answers
36 views

Conditional PS1

I'm basically trying to make my PS1 look like this when in a git repo: $ ~/Projects/Blah (master): Or if I'm not in a Git repo, I want it to look like this: $ ~/Projects/Blah: This is my current ...
9
votes
3answers
8k views

whiptail or dialog

I am going to create script which will use user input, so I decided to use whiptail, but little bit confuse that which one is portable and will work in ubuntu 10.x and higher and CentOs5.x and higher. ...
-4
votes
2answers
24 views

How to process only certain columns and ignore header and footer in delimited text file using awk?

I have an input text file called text.txt: Header Column1|Column2|Column3 C11|C12|C13 C21|C22|C23 C31|C32|C33 Footer My output should be: Column1|Column3 C11|C13 C21|C23 C31|C33 My command that ...
0
votes
0answers
52 views

What is the definition of an array being set?

The definition for an array being set is from bash manual: An array variable is considered set if a subscript has been assigned a value. The null string is a valid value. Does it mean that an ...
1
vote
1answer
23 views

Bash capturing asterisk inside a file [duplicate]

I have a text file which contains an asterisk as the first character in every line, when I try to process the file in a script like this: while read line; do out=$(echo $line | awk '{ print $3 }') ...
0
votes
1answer
30 views

When does an array variable represent the entire array, and when the element indexed by `0`?

Bash manual says: Referencing an array variable without a subscript is equivalent to referencing with a subscript of 0. In Bash or POSIX shell, is there some general rule for when an array ...
79
votes
2answers
3k views

Security implications of forgetting to quote a variable in bash/POSIX shells

If you've been following unix.stackexchange.com for a while, you should hopefully know by now that leaving a variable unquoted in list context (as in echo $var) in Bourne/POSIX shells (zsh being the ...
0
votes
1answer
3k views

LFTP mirror upload only non existing files to remote directory

Every 5 minutes some new files are downloaded via lftp to a local directory. I need to upload to another ftp only the non existing files. My script so far is: #! /bin/bash today=$(date +%Y%m%d) ...
2
votes
1answer
44 views

Tab to show directory contents

I use the terminal app on OSX. Whenever I cd into a deep directory I find it useful to display the successive directory contents as I go. By tapping tab when typing the filepath, it lets me see the ...
1
vote
1answer
25 views

how to inject keystrokes in a program like Safari from a bash script?

I am trying to automate some keypresses every few minutes. The exact timing is still undetermined. But basically I want to capture a live chat dialogue. I'm sure I could do this more elegantly. I ...
0
votes
0answers
38 views

Matching number using grep [on hold]

I have this text: yuiopao:##yuiopao:14975:Alex Vart student:/home/stud/yuiopao:/bin/bash polkovar:##polkovar:5004:John Adi student:/home/stud/polkovar:/bin/bash gfgfdgd:##gfgfdgd:11000:Alan ...
1
vote
1answer
41 views

Printing the file with number of hardlinks

I can print the number of hardlinks to files in directory by using find . type f -printf "%f %n\n" but this will also print the hardlink not only original files: Example: file1 is an original ...
1
vote
3answers
75 views

Delimiter in word splitting

In Bash, word splitting is a step in command line processing. From Bash Manual The shell treats each character of $IFS as a delimiter, and splits the results of the other expansions into words ...
21
votes
6answers
47k views

#!/bin/bash - no such file or directory

I've created a bash script but when I try to execute it, I get #!/bin/bash no such file or directory I need to run the command: bash script.sh for it to work. How can I fix this?
0
votes
1answer
39 views

command substitution - cat file inserts quotes

In bash, given these files: $ cat noquotes.txt s/a/b/g $ cat quotes.txt "s/a/b/g" Why does $ echo "aaa" | sed -e $(cat noquotes.txt) bbb succeed, but $ echo "aaa" | sed -e $(cat quotes.txt) ...
0
votes
0answers
30 views

In an array, does having an index/key implies that the element indexed by the index/key is set?

In an indexed/associative array, does having an index/key implies that the element indexed by the index/key is set? ( Note that by "set" above, I mean that a parameter/variable is set.) If not, ...
2
votes
1answer
35 views

Is a subscript to an indexed array an arithmetic expansion?

Quoting from the Bash manual: An indexed array is created automatically if any variable is assigned to using the syntax name[subscript]=value The subscript is treated as an arithmetic ...
0
votes
2answers
13 views

find composer global install path as root

I have some php packages installed globally using php composer within a script sudo -u me composer global require "phpmd/phpmd" I want to find the path of these globally installed php packages. ...
13
votes
7answers
23k views

How to restart the Python script automatically if it is killed or dies

I am running my Python script in the background in my Ubuntu machine (12.04) like this - nohup python testing.py > test.out & Now, it might be possible that at some stage my above Python ...
0
votes
3answers
46 views

sed substitution

I have a string as follows: /test/test/ 12 /test/test My goal is to turn it into: /test/est/ 12 /test/test This is the command: echo "$x" | sed 's@\(/*/\).@\1@g'" I am using at the moment but ...
3
votes
3answers
81 views

How to prevent script from deleting itself

Hi I'm creating a recycle bin script with the command name 'safe_rm'. I was wondering, how can I prevent the script from deleting its own file. I believe the readlink command is one solution however ...
2
votes
4answers
292 views

Generating QR code of very big file?

I want to generate a QR code of my 4096-bit armored GPG private key. The key is so big, the program qrencode seems to fail because of its size. $ gpg --export-secret-keys --armor > ~/private.key $ ...
3
votes
2answers
55 views

Wrap and indent text using coreutils

Short version I would like to create a tabular display of multiline text, similar to the following: all Build all targets document Create documentation of source files in the subfolders ...
1
vote
1answer
31 views

Rc.local not running commands properly

I am running arch Linux and have used this rc-local service: [Unit] Description=/etc/rc.local compatibility [Service] Type=oneshot ExecStart=/etc/rc.local RemainAfterExit=yes [Install] ...