Questions tagged [bash]
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. For shell scripts with errors/syntax errors, please check them with the shellcheck program (or in the web shellcheck server at https://shellcheck.net) before posting here.
25,612
questions
1319
votes
12
answers
3.1m
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How to correctly add a path to PATH?
I'm wondering where a new path has to be added to the PATH environment variable. I know this can be accomplished by editing .bashrc (for example), but it's not clear how to do this.
This way:
export ...
- 16.7k
765
votes
4
answers
518k
views
How to cycle through reverse-i-search in BASH?
In the terminal, I can type Ctrl + R to search for a matching command previously typed in BASH. E.g., if I type Ctrl + R then grep, it lists my last grep command, and I can hit enter to use it. This ...
- 4,705
695
votes
24
answers
261k
views
Preserve bash history in multiple terminal windows
I consistently have more than one terminal open. Anywhere from two to ten, doing various bits and bobs. Now let's say I restart and open up another set of terminals. Some remember certain things, some ...
- 15.6k
661
votes
19
answers
898k
views
How to get execution time of a script effectively?
I would like to display the completion time of a script.
What I currently do is -
#!/bin/bash
date ## echo the date at start
# the script contents
date ## echo the date at end
This just show's ...
- 26.1k
641
votes
3
answers
484k
views
Using "${a:-b}" for variable assignment in scripts
I have been looking at a few scripts other people wrote (specifically Red Hat), and a lot of their variables are assigned using the following notation
VARIABLE1="${VARIABLE1:-some_val}"
or some expand ...
- 7,299
567
votes
27
answers
840k
views
How can I resolve a hostname to an IP address in a Bash script?
What's the most concise way to resolve a hostname to an IP address in a Bash script? I'm using Arch Linux.
- 14.3k
525
votes
7
answers
253k
views
What is the difference between the Bash operators [[ vs [ vs ( vs ((?
I am a little bit confused on what do these operators do differently when used in bash (brackets, double brackets, parenthesis and double parenthesis).
[[ , [ , ( , ((
I have seen people use them on ...
- 5,399
523
votes
10
answers
909k
views
How to conditionally do something if a command succeeded or failed
How can I do something like this in bash?
if "`command` returns any error";
then
echo "Returned an error"
else
echo "Proceed..."
fi
Shinmaru
501
votes
4
answers
1.4m
views
In a bash script, using the conditional "or" in an "if" statement
This question is a sequel of sorts to my earlier question. The users on this site kindly helped me determine how to write a bash for loop that iterates over string values. For example, suppose that ...
- 15.8k
486
votes
14
answers
795k
views
How do I loop through only directories in bash?
I have a folder with some directories and some files (some are hidden, beginning with dot).
for d in *; do
echo $d
done
will loop through all files and directories, but I want to loop only through ...
- 26.9k
426
votes
16
answers
83k
views
In Bash, when to alias, when to script, and when to write a function?
It's taken me almost 10 years of Linux usage to ask this question. It was all trial and error and random late-night internet surfing.
But people shouldn't need 10 years for this. If I were just ...
- 13.3k
395
votes
17
answers
576k
views
How do I change the extension of multiple files?
I would like to change a file extension from *.txt to *.text. I tried using the basename command, but I'm having trouble on changing more than one file.
Here's my code:
files=`ls -1 *.txt`
for x in ...
- 4,279
395
votes
13
answers
666k
views
How can I get the size of a file in a bash script?
How can I get the size of a file in a bash script?
How do I assign this to a bash variable so I can use it later?
- 4,111
376
votes
12
answers
627k
views
How to view the output of a running process in another bash session?
I have left a script running on a remote machine from when I was locally working at it. I can connect over SSH to the machine as the same user and see the script running in ps.
$ ps aux | grep ...
- 7,212
370
votes
6
answers
382k
views
Why does my shell script choke on whitespace or other special characters?
… or an introductory guide to robust filename handling and other string passing in shell scripts.
I wrote a shell script which works well most of the time. But it chokes on some inputs (e.g. on some ...
362
votes
13
answers
376k
views
How to remove a single line from history?
I'm working in Mac OSX, so I guess I'm using bash...?
Sometimes I enter something that I don't want to be remembered in the history. How do I remove it?
- 7,519
352
votes
4
answers
104k
views
How do I clear Bash's cache of paths to executables?
When I execute a program without specifying the full path to the executable, and Bash must search the directories in $PATH to find the binary, it seems that Bash remembers the path in some sort of ...
- 3,745
348
votes
6
answers
485k
views
How to define 'tab' delimiter with 'cut' in Bash?
Here is an example of using cut to break input into fields using a space delimiter, and obtaining the second field:
cut -f2 -d' '
How can the delimiter be defined as a tab, instead of a space?
- 3,583
343
votes
4
answers
83k
views
334
votes
4
answers
420k
views
How to get the pid of the last executed command in shell script?
I want to have a shell script like this:
my-app &
echo $my-app-pid
But I do not know how the get the pid of the just executed command.
I know I can just use the jobs -p my-app command to grep ...
- 5,469
328
votes
13
answers
222k
views
How to colorize output of git?
Is there a way to color output for git (or any command)?
Consider:
baller@Laptop:~/rails/spunky-monkey$ git status
# On branch new-message-types
# Changes not staged for commit:
# (use "git add &...
- 7,519
315
votes
3
answers
338k
views
How can I make "Press any key to continue" [duplicate]
I'm making a script to install my theme, after it finished installing it will appear the changelog and there will be "Press any key to continue" so that after users read the changelog then press any ...
- 3,671
314
votes
12
answers
565k
views
How can I test if a variable is empty or contains only spaces?
The following bash syntax verifies if param isn't empty:
[[ ! -z $param ]]
For example:
param=""
[[ ! -z $param ]] && echo "I am not zero"
No output and its fine.
But when param is ...
- 6,883
313
votes
5
answers
260k
views
Why doesn't my Bash script recognize aliases?
In my ~/.bashrc file reside two definitions:
commandA, which is an alias to a longer path
commandB, which is an alias to a Bash script
I want to process the same file with these two commands, so I ...
- 10.2k
312
votes
5
answers
1.1m
views
How can I get the current working directory? [duplicate]
I want to have a script that takes the current working directory to a variable. The section that needs the directory is like this dir = pwd. It just prints pwd how do I get the current working ...
user104976
308
votes
25
answers
902k
views
Colorizing your terminal and shell environment?
I spend most of my time working in Unix environments and using terminal emulators. I try to use color on the command line, because color makes the output more useful and intuitive.
What options exist ...
- 18.9k
303
votes
10
answers
766k
views
What is the "eval" command in bash?
What can you do with the eval command? Why is it useful? Is it some kind of a built-in function in bash? There is no man page for it..
- 38.4k
286
votes
4
answers
354k
views
What is the meaning of IFS=$'\n' in bash scripting?
At the beginning of a bash shell script is the following line:
IFS=$'\n'
What is the meaning behind this collection of symbols?
- 25.1k
267
votes
19
answers
429k
views
How to add a newline to the end of a file?
Using version control systems I get annoyed at the noise when the diff says No newline at end of file.
So I was wondering: How to add a newline at the end of a file to get rid of those messages?
- 14.4k
267
votes
3
answers
790k
views
What is the purpose of .bashrc and how does it work?
I found the .bashrc file and I want to know the purpose/function of it. Also how and when is it used?
- 23.4k
266
votes
4
answers
46k
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 ...
- 504k
264
votes
12
answers
308k
views
Execute a command once per line of piped input?
I want to run a java command once for every match of ls | grep pattern -. In this case, I think I could do find pattern -exec java MyProg '{}' \; but I'm curious about the general case - is there an ...
- 3,553
263
votes
9
answers
193k
views
How to determine where an environment variable came from?
I have a Linux instance that I set up some time ago. When I fire it up and log in as root there are some environment variables that I set up but I can't remember or find where they came from.
I've ...
- 2,733
254
votes
14
answers
361k
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 ...
- 39.2k
252
votes
12
answers
129k
views
Is there a one-liner that allows me to create a directory and move into it at the same time?
I find myself repeating a lot of:
mkdir longtitleproject
cd longtitleproject
Is there a way of doing it in one line without repeating the directory name? I'm on bash here.
- 3,179
249
votes
5
answers
114k
views
What does env x='() { :;}; command' bash do and why is it insecure?
There is apparently a vulnerability (CVE-2014-6271) in bash: Bash specially crafted environment variables code injection attack
I am trying to figure out what is happening, but I'm not entirely sure ...
- 13.5k
247
votes
6
answers
181k
views
How can I delete a word backward at the command line (bash and zsh)?
How can I delete a word backward at the command line? I'm truly used to some editors deleting the last 'word' using Ctrl+Backspace, and I'd like that functionality at the command line too.
I am ...
- 2,719
239
votes
10
answers
148k
views
Terminal prompt not wrapping correctly
I have an issue where if I type in very long commands in bash the terminal will not render what I'm typing correctly. I'd expect that if I had a command like the following:
username@someserver ~/...
- 2,500
237
votes
4
answers
169k
views
Combined `mkdir` and `cd`? [duplicate]
is there any way (what is the easiest way in bash) to combine the following:
mkdir foo
cd foo
The manpage for mkdir does not describe anything like that, maybe there is a fancy version of mkdir? I ...
- 3,498
236
votes
2
answers
418k
views
There are stopped jobs (on bash exit)
I get the message There are stopped jobs. when I try to exit a bash shell sometimes. Here is a reproducible scenario in python 2.x:
ctrl+c is handled by the interpreter as an exception.
ctrl+z 'stops'...
- 4,144
218
votes
9
answers
290k
views
Looping through files with spaces in the names? [duplicate]
I wrote the following script to diff the outputs of two directores with all the same files in them as such:
#!/bin/bash
for file in `find . -name "*.csv"`
do
echo "file = $file";
diff $...
- 6,953
218
votes
3
answers
1.0m
views
How do I remove a directory and all its contents?
In bash all I know is that
rmdir directoryname
will remove the directory but only if it's empty. Is there a way to force remove subdirectories?
- 2,475
216
votes
4
answers
207k
views
What does <<< mean? [duplicate]
What does <<< mean? Here is an example:
$ sed 's/a/b/g' <<< "aaa"
bbb
Is it something general that works with more Linux commands?
It looks like it's feeding the sed program with ...
- 2,315
215
votes
8
answers
362k
views
How to debug a bash script?
I'm having some problems with some scripts in bash, about errors and unexpected behaviors. I would like to investigate the causes of the problems so I can apply fixes. Is there a way I can turn some ...
- 35k
213
votes
3
answers
133k
views
Are there naming conventions for variables in shell scripts?
Most languages have naming conventions for variables, the most common style I see in shell scripts is MY_VARIABLE=foo. Is this the convention or is it only for global variables? What about variables ...
- 5,011
212
votes
6
answers
590k
views
remove particular characters from a variable using bash
I want to parse a variable (in my case it's development kit version) to make it dot(.) free. If version='2.3.3', desired output is 233.
I tried as below, but it requires . to be replaced with another ...
- 4,678
209
votes
6
answers
424k
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 a background 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 ...
- 3,830